How Belief Works is an ongoing series of articles on the psychology of belief that's best read in sequence.

The truth about how beliefs form is even simpler than the two false conceptions of belief formation that I analysed in the previous article. But unlike them it's initially highly counterintuitive. And yet, just as logic alone can disprove the idea that the formation of a belief is us assessing that the claim concerned is true, logic alone can prove that this alternative conception of belief formation is correct. And this truth has profound implications for our understanding of human psychology – and therefore also has profound implications for our lives.

A radical theory of belief formation

This theory of belief formation isn't new. It was originally proposed by the prominent 17th-century philosopher Baruch Spinoza, in his posthumous 1677 book Ethics, but has only ever been supported by a small minority of scholars of the mind.

It might be thought, before even knowing what the theory is, that its failure to gain wide acceptance by scholars after more than three centuries suggests that it's wrong. However, the theory that the Earth goes around the Sun, rather than vice versa, was also initially highly counterintuitive – mainly due to the Sun's daily apparent motion across the sky, and our inability to feel Earth's actual motion – and only became widely accepted by scholars more than nineteen centuries after it was first proposed, by the ancient Greek astronomer and mathematician Aristarchus of Samos.

Spinoza's theory is this. Consider that a claim enters our mind via one of four cognitive processes:

• comprehension – when the claim is communicated to us via some medium that we perceive, which is normally voice or text

• reason – when the claim is a conclusion

• imagination – when we generate the claim without using reason

• recollection – when we retrieve the claim from our memory.

Spinoza asserted that the mere entrance of a claim into our mind causes us to believe it.

This assertion can seem obviously wrong – which can itself seem to disprove it. It can seem obvious from experience that merely comprehending, imagining-up or recalling a claim doesn't cause us to believe it. Regarding reason, a conclusion is by definition a belief. But the theory implies that our belief of this claim upon it entering our mind is due merely to that entrance, rather than being due to the claim being the product of our reason. And that can seem obviously contrary to both the concept and experience of reasoning.

But closer analysis reveals that Spinoza's theory actually isn’t contrary to our experience of claims entering our mind via any of these processes. And although the theory is indeed contrary to the current conception of reasoning, analysis reveals that there’s actually no reason to think that this conception can’t be replaced by one that agrees with the theory.

Also, there’s increasing experimental support for the theory. For example, a 2022 paper by neuroscientists at the universities of Harvard, Princeton and Dartmouth in the US presents brain scan evidence which seems to support the theory.

And the first academic conference on Spinozan belief formation took place in 2018, in the US. Another is planned for 2026, in the Netherlands, where Spinoza was born.

To see why Spinoza was right, consider first the two ways that a claim can be involved in our thinking.

The two ways that a claim can be involved in our thinking

If claim X is involved in our thinking then we're either thinking X or thinking about X. For example, if the claim David is vegetarian is involved in our thinking then we're either thinking 'David is vegetarian' or thinking about the claim David is vegetarian.

Thinking claim X is the mental state of believing X. For example, thinking 'David is vegetarian' is the mental state of believing that a particular person that we know of called David is vegetarian. Indeed, we often use the word think to refer to the mental state of belief. For example, we may refer to Amy’s mental state of believing that David is vegetarian by saying 'Amy thinks that David is vegetarian'.

Consider the mental state of concluding X. By definition, concluding X involves thinking X. For example, by definition, concluding 'David is vegetarian' involves thinking 'David is vegetarian'. And, also by definition, to conclude X is to believe X. 

We can of course continue to hold belief X after thinking X, when our belief exists not as a mental state with an associated brain state but solely as a brain state, in a memory area of the brain. So believing X doesn't necessarily involve currently thinking X. That is, the psychological state of belief doesn't always involve the mental state of belief, although it always begins with that mental state, however briefly.

According to some psychologists and philosophers, we actually don’t think in the language, or languages, that we communicate in, contrary to our apparent experience of thinking. Instead, the medium of thought is a universal mental language called the language of thought or mentalese. But the logic of the argument presented in this article – and of that presented in the next – equally applies to this understanding of thought.

Regarding thinking about claim X, we obviously can do this while not believing X. For example, we obviously can think about the claim David is vegetarian while believing that David isn't vegetarian, or believing that it's uncertain whether David is vegetarian. This fact can seem to disprove Spinoza's theory, but, as will become apparent later, it doesn't.

We can actually think about a claim without it even existing in our mind. For example, if we know that David told Amy what his dietary restrictions are, but don't know what he said, then this claim doesn't exist in our mind, but we can think about it in the sense of thinking about its existence in David and Amy's minds. But I'm concerned in this argument with thinking about claim X in the sense that involves X existing in our mind, as thinking X does. And it’s this sense that I mean when I subsequently refer to thinking about X.

It might be thought that thinking 'I believe claim X' is another form of the mental state of believing X, and so the mental state of believing X can involve thinking about X. But thinking 'I believe claim X' is actually the mental state of believing that we believe X. Likewise, it might be thought that saying 'I believe claim X' is an expression of our belief of X, and so the mental state of believing X can involve thinking about X. But saying 'I believe claim X' is actually our expression of our belief that we believe X. Our expression of simply our belief of X instead involves saying simply X.

In the previous article I explained that claim X and the claim X is true are different claims, and so belief X and the belief X is true are by definition different beliefs. The difference between these beliefs aligns with the difference between thinking X and thinking about X. That is, whereas the mental state of believing X involves thinking X, the mental state of believing X is true involves thinking 'X is true', and thinking that claim X is a true claim involves thinking about X.

Now consider how the content of claim X exists in our mind as we’re thinking X and thinking about X.

The two ways that the content of a claim can exist in our mind

A claim can of course be about anything. But all claims are ultimately about the same thing: reality. The definition of a true claim is a claim that matches reality, and the definition of a false claim is a claim that doesn't match reality.

Reality includes the content of our own mind and the minds of others. So the content of our imagination, which is often contrasted with reality, is actually part of reality in the sense that it's part of mental reality. For example, the content of a fictional story that we're reading is part of reality in the sense that it exists in our imagination and is therefore part of mental reality.

Concepts, being abstract, are also often contrasted with reality. But concepts are ideas and so exist in our mind. Therefore concepts – including mathematical, scientific and philosophical concepts – are also part of reality in the sense of being part of mental reality.

Even moral and political principles, which are claims about how we should live rather than about how we do live, are claims about reality, because they're claims about moral or political reality. For example, the moral claim that we should help people in need is the claim that do have a moral obligation to help people in need. Likewise, the political claim that government should be democratic is the claim that democracy is the best form of government.

A claim is analogous to a picture, in the sense that the content of both is a representation of an aspect of reality, however accurate. Indeed, we sometimes say that a particular description 'paints a picture'. Even if a picture is of a scene that existed only in the imagination of the picture’s creator, the content of that picture is a representation of the content of that imagination, which is part of mental reality.

There are of course different ways to create a picture, such as painting, drawing, using art software, or photography. Consider a painting of an outdoor scene.

The painting is ultimately just a collection of patches of paint on a surface. The picture we see, of an outdoor scene, as we look at this collection of patches of paint is our brain's interpretation of this collection of patches of paint. That is, the picture isn't the painting but what forms in our vision as we look at this collection of patches of paint. However, because we see this collection of patches of paint as a picture, the painting and the picture seem to be the same thing.

So what we refer to as 'a painting of an outdoor scene' isn't itself a picture of an outdoor scene, and is instead a painting that creates in our vision a picture of an outdoor scene. What we refer to as 'a photorealistic painting of an outdoor scene' therefore actually isn't itself photorealistic, and is instead a collection of patches of paint that creates in our vision a photorealistic picture of an outdoor scene

The relationship between this picture and the painting is analogous to the relationship between a claim and the sentence that expresses it. Such a sentence is a declarative sentence – a sentence that declares something, as opposed to one that expresses either a question, advice, an instruction, a command, a request or an exclamation.

A declarative sentence is ultimately just a string of words, but together they express a claim. That is, the claim isn't the sentence – the string of words – but what is asserted by the sentence. In philosophy and psychology the term proposition is normally used instead of claim. And Oxford University Press's A Dictionary of Psychology defines this sense of the term proposition as:

The meaning conveyed by a declarative sentence ... The proposition is not the sentence itself but its meaning. ...

For example, when we refer to 'the claim David is vegetarian' we're referring not to the sentence David is vegetarian, but to what's asserted by this sentence. We refer to 'the claim David is vegetarian’, even though David is vegetarian is a sentence, because, by definition, we can only ever express this claim by using a sentence that expresses it. But doing so can lead to the claim and the sentence being conflated.

The difference between the sentence David is vegetarian and the claim David is vegetarian is apparent from the fact that, by definition, this claim is also made by other sentences which have the same meaning, such as David follows a vegetarian diet, David adheres to vegetarianism, David abstains from eating meat, David est végétarien and David ist vegetarisch. Logically, if sentence X and claim X were the same thing then that claim couldn't also be the same thing as a different sentence.

Analogously, as we look at the painting of an outdoor scene, the picture we see is the same as the picture we see as we look at a print of this painting, even though the painting is made-up of paint brushstrokes whereas the print is made-up of microscopic dots of ink, and even if the dimensions of the print are different from those of the painting. So the painting and the picture are indeed not the same thing. That is, logically, if the painting and the picture were the same thing then the picture couldn't also be the same thing as the print, which is different from the painting.

Also, there can be multiple legitimate interpretations of what claim is being made by a sentence. For example, the sentence Emma likes racing cars can be interpreted as making either the claim that Emma likes cars designed for racing, or the claim that Emma likes racing in cars. Logically, if sentence X and claim X were the same thing then that sentence couldn't also be the same thing as a different claim.

Analogously, when we look at this drawing – the 'rabbit-duck illusion' – we see a picture of the head of either a rabbit – facing right – or a duck – facing left:

So each picture is indeed not the drawing itself. That is, logically, if the drawing and either picture were the same thing then the drawing couldn't also be the same thing as the other, different, picture.

Given that the claim David is vegetarian is what is asserted by the sentence David is vegetarian, it’s the content of this sentence. And the content of a declarative sentence is an idea, a concept. So the claim David is vegetarian is the concept that David is vegetarian.

It might be thought that the claim that David is vegetarian and the concept that David is vegetarian are different things. That is, it might be thought that whereas the former involves someone claiming that David is vegetarian, the latter doesn't, because it's merely the idea that David is vegetarian.

But consider that claim X can be generated and communicated without anyone actually claiming X. For example, if we make-up the claim David is vegetarian, and then present it to others as a claim that we've made-up, then we've generated and communicated this claim without actually claiming that David is vegetarian.

So although a claim is by definition asserted by a declarative sentence, it hasn't necessarily been asserted by a person. That is, a claim, an assertion, is in itself merely a concept, an idea. Indeed, we refer to the concept that David is vegetarian using – as I just did – the sentence David is vegetarian, which expresses the claim that David is vegetarian.

So the claim that David is vegetarian actually doesn't in itself involve someone claiming that David is vegetarian, and is instead merely the concept, the idea, that David is vegetarian.

Of course, not all concepts are claims. For example, the concept of vegetarianism is the concept of abstinence from meat, and the words vegetarianism and abstinence from meat don't express claims – that is, they don't form declarative sentences. But all claims are concepts.

The fact that a claim is a concept means that, whereas a declarative sentence and its content – a claim – aren’t the same thing, a claim and its content are. For example, the content of the claim David is vegetarian is the concept that David is vegetarian, which is the claim David is vegetarian. So this claim and its content are simply the same thing, rather than the latter being what is asserted by the former.

Indeed, to say that the claim David is vegetarian matches reality is in itself to say that the content of this claim matches reality. And to say that the claim David is vegetarian is what is asserted by the sentence David is vegetarian is in itself to say that the content of this claim is what is asserted by this sentence.

Analogously, whereas the painting of an outdoor scene and its content – the picture of that scene – aren’t the same thing, the picture and its content are. An aspect of the picture – as opposed to an aspect of the painting, such as the brushwork – is an aspect of the content of the picture. And the picture as a whole is the whole content of the picture.

Indeed, to say that the picture is an accurate representation of the outdoor scene is in itself to say that the content of the picture is an accurate representation of that scene. And to say that the picture is what we see as we look at the painting is in itself to stay that the content of the picture is what is what we see as we look at the painting.

In the case of the rabbit-duck illusion, to stay that the picture changes depending on how our brain interprets the drawing is in itself to stay that the content of the picture changes depending on how our brain interprets the drawing.

An advantage of referring to, for example, ‘the content of the claim David is vegetarian’ rather than just ‘the claim David is vegetarian’ is that the latter wording, unlike the former, could be misunderstood as referring to the sentence David is vegetarian rather than the content of this sentence. Analogously, in the case of the picture we see as we look at the painting of an outdoor scene, an advantage of referring to ‘the content of the picture’ rather than just ‘the picture’ is that the latter wording, unlike the former, could be misunderstood as referring to the painting rather than the picture.

Indeed, consider the wording 'the claim David is vegetarian is the concept that David is vegetarian'.

Again, the content of this wording can seem wrong because it can seem that the claim that David is vegetarian involves someone claiming that David is vegetarian, whereas the concept that David is vegetarian doesn't, because it's merely the idea that David is vegetarian. But consider the alternative wording 'the content of the claim David is vegetarian is the concept that David is vegetarian'. The content of this wording doesn't seem wrong for the above reason even for someone who wrongly believes that claim X involves in itself someone claiming X.

However, the content of the original wording can also seem wrong because that wording can be misunderstood as saying that the sentence David is vegetarian is the concept that David is vegetarian, when the latter is obviously the content of the former. But consider again the alternative wording 'the content of the claim David is vegetarian is the concept that David is vegetarian'. The content of this wording doesn't seem wrong for the above reason even for someone who wrongly conflates claim X and sentence X.

Also note that the concept that David is vegetarian can also be referred to as the concept of David being vegetarian. So the claim David is vegetarian can be also be referred to as the concept of David being vegetarian. Alternatively stated, the content of the claim David is vegetarian can also be referred to as the concept of David being vegetarian.

Now consider the following thought experiment.

Imagine a room with a fake window. The fake window, on an external wall, consists of a real window frame surrounding a photorealistic painting of a daytime outdoor scene, without any space between the edge of the painting and inside edge of the frame. It's located opposite the room's entrance, so when someone enters the room they’re looking at it face-on. And the scene they see within the frame, in that moment, is what they'd see from the room's entrance, in the daytime, through a real window in the same location. Also, that scene is one in which an absence of movement isn't unusual.

Now imagine entering the room for the first time, during the daytime, with the room's lighting on, and without knowledge of the fake window. If upon us looking at the fake window it creates the illusion of a real window, at least initially, then our visual experience will consist of us apparently directly seeing a real outdoor scene through a real window. And if the fake window doesn't create this illusion, even initially, then our visual experience will consist of us seeing merely a picture of an outdoor scene, in a fake window.

So upon us looking at the fake window the content of the picture exists in our vision either as the content of a picture of an outdoor scene or as a real outdoor scene.

These two ways that the content of the picture can exist in our vision are the only two logically possible ways that it can exist in our vision. If the content of the picture doesn't exist in our vision as the content of a picture of an outdoor scene then the only other logical possibility is that it exists in our vision as a real outdoor scene – and vice versa. That is, if our visual experience doesn’t consist of us seeing a picture of an outdoor scene then the only other logical possibility is that it consists of us apparently directly seeing a real outdoor scene – and vice versa.

And these two, and only two, logically possible ways that the content of the picture can exist in our vision are analogous to the two, and only two, logically possible ways that the content of a claim can exist in our mind.

The picture's content existing in our vision as the content of a picture is analogous to a claim's content existing in our mind as the content of a claim. And it might be thought that when a claim exists in our mind the only conceivable way for its content to exist in our mind is as the content of a claim. But without consideration of the above thought experiment it might similarly be thought, regarding the picture that exists in our vision as we look at a pictorial painting, that the only conceivable way for its content to exist in our vision is as the content of a picture.

Consider assessing that claim X is a true claim.

As I explained in the previous article, this assessment is based on our belief of X. By definition, a claim is a true claim if, and only if, it matches reality. So the only way to assess whether a claim is a true claim is to assess whether it matches reality. And the only way to assess whether a claim matches reality is to compare it with reality. But, logically, when we compare a claim with reality we can only ever compare it with what we believe about the relevant aspect of reality at the moment of the comparison, even when the comparison uses the current content of our senses.

So our assessment that claim X is a true claim is based on us having a conception of both the content of claim X and the relevant aspect of reality, and then concluding that they match. That is, that assessment is based on the content of claim X existing in our mind as the content of a claim and as an aspect of reality. For example, our assessment that the claim David is vegetarian is a true claim is based on the content of this claim existing in our mind as the content of a claim and an aspect of reality.

In the case of assessing that claim X is a false claim, this assessment is based on us having a conception of both the content of claim X and the relevant aspect of reality, and then concluding that they don't match. That is, that assessment is based on the content of claim X existing in our mind merely as the content of a claim.

So just as, in the fake window thought experiment, the content of the picture can exist in our vision as the content of a picture of an outdoor scene or as a real outdoor scene, the content of a claim can exist in our mind as the content of a claim or as an aspect of reality.

Again, a picture and its content are the same thing, and a claim and its content are the same thing. So it can alternatively be said that, just as, in the fake window thought experiment, the picture can exist in our vision as a picture of an outdoor scene or as a real outdoor scene, a claim can exist in our mind as a claim or as an aspect of reality.

Also, just as, in the fake window thought experiment, the content of the picture exists in our vision as either the content of a picture of an outdoor scene or a real outdoor scene, the content of claim X can't simultaneously exist in our mind as the content of claim X and as an aspect of reality. The former involves thinking about X, whereas the latter is the mental state of believing X, which involves thinking X, and we can't be simultaneously thinking about X and thinking X.

It therefore might be wondered how we can conclude there's a match between the content of claim X and the relevant aspect of reality if our conceptions of them can't exist 'side-by-side' in our mind. To see how we can conclude this, consider the claim David is vegetarian.

Upon embarking on our assessment of whether this claim is a true claim we reason that it will be if David is vegetarian – so at this point the content of the claim only exists in our mind as the content of a claim. And at some subsequent point – possibly in the next moment – we think/believe 'David is vegetarian' – and so the content of the claim now only exists in our mind as an aspect of reality. But given this thought we subsequently conclude that the claim David is vegetarian is a true claim – and so the content of the claim now again only exists in our mind as the content of a claim.

So in this way we can compare the claim with reality, and conclude that they match, without the content of the claim simultaneously existing in our mind as the content of the claim and as an aspect of reality.

In the previous two articles I showed that particular definitions of belief are wrong. The above analysis provides a correct definition of belief: a psychological state in which the content of a claim exists in the mind, or at least memory, as an aspect of reality.

Indeed, although thinking X – the mental state of believing X – involves, by definition, the content of X existing in our mind, it can't, as a matter of logic, in itself involve that content existing in our mind as the content of a claim, given that that involves, by definition, thinking about claim X. For example, although thinking ‘David is vegetarian’ involves, by definition, the content of this claim existing in our mind, it can’t, as a matter of logic, in itself involve that content existing in our mind as the content of a claim, because that involves, by definition, thinking about this claim.

Given that a claim and its content are the same thing, it can alternatively be said that although thinking X involves, by definition, X existing in our mind, it can't, as a matter of logic, in itself involve this claim existing in our mind as a claim, because that involves, by definition, thinking about claim X. For example, although thinking ‘David is vegetarian’ involves, by definition, this claim existing in our mind, it can’t, as a matter of logic, in itself involve this claim existing in our mind as a claim, because that involves, by definition, thinking about this claim.

Analogously, regarding the fake window thought experiment, given that a picture and its content are the same thing, instead of saying that the content of the picture can exist in our vision without existing in our vision as the content of a picture, it can be said that the picture can exist in our vision without existing in our vision as a picture. But without consideration of this thought experiment it might be thought, regarding the picture that exists in our vision as we look at a pictorial painting, that the only conceivable way for the picture to exist in our vision is as a picture.

Also, again, a claim is a concept. So it can also alternatively be said that although thinking X involves, by definition, concept X existing in our mind, it can't in itself involve this concept existing in our mind as a concept. For example, although thinking ‘David is vegetarian’ involves, by definition, the concept of David being vegetarian existing in our mind, it can’t in itself involve this concept existing in our mind as a concept.

Given the speediness of the brain, which functions on the timescale of milliseconds, we may think about claim X so soon before or after thinking X that our thinking X can seem to in itself involve thinking about X. So thinking X can seem to in itself involve the content of X existing in our mind as the content of a claim. That is, thinking X can seem to in itself involve this claim existing in our mind as a claim – it can seem to in itself involve this concept existing in our mind as a concept.

It might be thought that if as we’re thinking ‘David is vegetarian’ the content of this claim can’t exist in our mind as the content of this claim, because that would involve thinking about this claim, then perhaps it exists in our mind as the content of a claim without existing in our mind as the content of a specific claim, and so doesn't involve thinking about the claim David is vegetarian.

However, given that a claim and its content are the same thing, the existence of the content of the claim David is vegetarian in our mind as the content of a claim is the existence of the claim David is vegetarian in our mind as a claim – which by definition involves thinking about this claim. That is, the content of the claim David is vegetarian can’t exist in our mind as the content of a claim without existing in our mind as the content of the specific claim David is vegetarian.

Analogously, in the fake window thought experiment, the content of the picture obviously can’t exist in our vision as the content of a picture without existing in our vision as the content of that specific picture.

If thinking claim X can't in itself involve the content of X existing in our mind as the content of a claim – if it can't in itself involve this claim existing in our mind as a claim, if it can't in itself involve this concept existing in our mind as a concept – then the only other logical possibility is that it involves the content of X – this claim, this concept – existing in our mind as an aspect of reality.

That is, given that all claims are about an aspect of reality, if thinking X doesn’t in itself involve the content of X existing in our mind as the content of a claim about an aspect of reality, then the only other logical possibility is that it involves that content existing in our mind simply as that aspect of reality. For example, if thinking ‘David is vegetarian’ doesn’t in itself involve the content of this claim existing in our mind as the content of a claim about an aspect of reality, then the only other logical possibility is that it involves that content existing in our mind simply as that aspect of reality.

And the conclusion that thinking X must involve the content of X existing in our mind as an aspect of reality obviously accords with the fact that thinking X is the mental state of believing X.

Regarding the conclusion that thinking claim X involves this concept existing in our mind not as a concept, but as an aspect of reality, it might be thought that, by definition, the content of an abstract claim, such as The death penalty is wrong, can only exist in our mind as a concept. That is, it might be thought that the content of the claim The death penalty is wrong can only exist in our mind as the concept that the death penalty is wrong. So thinking/believing 'The death penalty is wrong' must involve the content of this claim existing in our mind as a concept that's an aspect of reality.

However, given that the concept that the death penalty is wrong is the claim The death penalty is wrong, this concept existing in our mind as a concept is this concept existing in our mind as a claim, which involves thinking about this claim. So thinking even this abstract claim can't in itself involve its content existing in our mind as a concept. That is, thinking/believing 'The death penalty is wrong' must in itself involve the content of this moral claim existing in our mind not as a moral concept that's an aspect of reality, but simply as an aspect of morality reality.

The content of claim X, abstract or not, existing in our mind as an aspect of reality, as we’re thinking/believing X, isn't the mental state of thinking/believing that the content of X is an aspect of reality. The latter involves thinking not simply X, but 'The content of claim X is an aspect of reality'. And it therefore involves thinking about X, with the content of X existing in our mind as the content of a claim. Indeed, it's the mental state of thinking/believing that X is a true claim.

Also, the content of X existing in our mind as an aspect of reality, as we’re thinking/believing X, is different from the existence of that content in our mind as the content of a claim that we believe. The latter involves thinking/believing not simply X, but ‘I believe X’. That is, it's the mental state of believing that we believe X. And it therefore involves thinking about X, with the content of X existing in our mind as the content of a claim.

Perhaps the best way to convey the idea of the content of claim X existing in our mind not as the content of a claim, but as an aspect of reality, is to refer, as I did, to the fact that assessing that X is a true claim is based on us having a conception of both the content of X and the relevant aspect of reality, and then concluding that they match. And the fake window thought experiment, with the content of the picture possibly existing in our vision not as the content of a picture of an outdoor scene but as a real outdoor scene, helps convey this idea by analogy.

The difference between thinking X and thinking about X has the logical, but counterintuitive, implication that a claim can exist in our mind without us thinking about it. That is, although thinking X involves, by definition, X existing in our mind, it doesn’t in itself involve thinking about X. If we're thinking about X while apparently thinking X then we're actually not at that moment thinking X. Although, again, given the brain's speediness, we may think about X so soon before or after thinking X that our thinking X can seem to in itself involve thinking about X.

But, despite this logic, it can still seem contradictory to say that, for example, thinking ‘David is vegetarian’ doesn't in itself involve thinking about this claim that David is vegetarian. Indeed, thinking any claim necessarily involves thinking about something, and if thinking ‘David is vegetarian’ doesn't in itself involve thinking about the claim that David is vegetarian then what else could it involve thinking about?

This apparent paradox is resolved when it's understood that although thinking ‘David is vegetarian’ involves, by definition, this claim existing in our mind, the claim exists in our mind not as a claim, but as an aspect of reality. That is, although thinking ‘David is vegetarian’ involves thinking about David being vegetarian, David being vegetarian exists in our mind not as a mere claim, but as an aspect of reality.

So the mental state of believing claim X doesn't in itself actually involve thinking about this claim. For example, the mental state of believing the claim David is vegetarian doesn't in itself actually involve thinking about this claim. Again, thinking 'I believe the claim David is vegetarian', which does involve thinking about the claim David is vegetarian, is the mental state not of believing the claim David is vegetarian, but of believing that we believe the claim David is vegetarian.

Note that although the content of both a picture and a claim is a representation of an aspect of reality, however accurate, pictures and claims are themselves aspects of reality. Again, the picture we see as we look at a painting of an outdoor scene is what forms in our vision as we look at this collection of patches of paint on a surface. So that picture is an aspect of mental reality. And a claim, being a concept, is an idea, and so is also an aspect of mental reality.

Indeed, a picture can part of the scene in another picture, and a claim can be referred to by another claim. Also, a picture can be referred to by a claim, and the sentence expressing a claim can appear in a picture.

In the fake window thought experiment, although the content of the picture can exist in our vision either as the content of a picture of an outdoor scene or as a real outdoor scene, both involve that content existing in our vision as an aspect of reality. By definition, anything that exists in our vision does so at least as an aspect of mental reality. In the case of seeing a picture, again, the fact that we see this collection of patches of paint as a picture means that the painting and the picture can seem to be the same thing. So the picture that forms in our vision seems to be a part of the scene in front of us.

Likewise, although I've been saying that the content of claim X can exist in our mind as the content of a claim or as an aspect of reality, the former is actually also the content of X existing in our mind as an aspect of reality, albeit in a different way. By definition, anything that exists in our mind does so at least as an aspect of mental reality. I've been referring to the content of X existing in our mind as an aspect of reality to solely mean that content existing in our mind not as merely the content of this claim about an aspect of reality, but as that aspect of reality – and for conciseness I'll continue to do so in subsequent sections.

So although, by definition, a false claim doesn't match reality, it's also an aspect of reality. This wording can seem contradictory, and a better wording is: although, by definition, a false claim about an aspect of reality doesn't match that aspect of reality, it's also itself an aspect of reality.

Likewise, a true claim, by definition, matches reality, and is also an aspect of reality. This wording can instead seem redundant, and a better wording is: a true claim about an aspect of reality, by definition, matches that aspect of reality, and is also itself an aspect of reality.

The fact that claims are themselves aspects of reality means that the definition of belief that I gave earlier – a psychological state in which the content of a claim exists in the mind, or at least memory, as an aspect of reality – is more precisely expressed as: a psychological state in which the content of a claim exists in the mind, or at least memory, not as the content of this claim about an aspect of reality, but as that aspect of reality.

Thinking X is always believing X

It might be thought that thinking claim X actually isn’t always the mental state of believing X. That is, it can seem obvious that if we don't believe X – whether we believe a contrary claim or don't hold a belief on the subject of X – but we deliberately think X, like a silent mantra, doing so won't cause us to believe X. For example, it can seem obvious that if we believe that David isn’t vegetarian, but we deliberately think 'David is vegetarian', like a silent mantra, doing so won't cause us to believe that David is vegetarian.

I've indeed so far only been concerned with organically thinking X – that is, when our thinking X is either a recollection of an apparent fact or a conclusion, each of which are by definition the mental state of believing X. But the conclusion in the previous section that thinking X necessarily involves the content of X existing in our mind as an aspect of reality, which is the mental state of believing X, equally applies to deliberately thinking X. And this isn’t, upon analysis, contrary to our experience of deliberately thinking X.

Thinking X is different from thinking about X whether the former is organic or deliberate. For example, although deliberately thinking 'David is vegetarian' involves, by definition, thinking about this claim immediately beforehand, and we may also think about it immediately afterwards, doing so doesn’t in itself involve thinking about it.

If we're thinking about claim X while apparently deliberately thinking X then we're actually not at that moment thinking X. Although, given the brain's speediness, we can think about X so soon before, and possibly after, deliberately thinking X that our deliberately thinking X can seem to in itself involve thinking about X. Also, we may think about X during our attempt to think X, which can add to the sense that deliberately thinking X involves, in itself, thinking about X, even though that thinking about X actually interrupts our thinking X.

And, again, the content of X existing in our mind as the content of a claim involves, by definition, thinking about X. So although deliberately thinking X involves, by definition, the content of X existing in our mind, it can't in itself involve that content existing in our mind as the content of a claim.

And the only two logically possible ways that the content of a claim can exist in our mind are as the content of a claim or as an aspect of reality. So deliberately thinking X must involve the content of X existing in our mind as an aspect of reality.

And the content of X existing in our mind as an aspect of reality is the mental state of believing X. So even deliberately thinking X is the mental state of believing X.

And this belief continues beyond us deliberately thinking X, due to the content of X being stored in our memory as an aspect of reality. Again, believing X doesn't necessarily involve currently thinking X.

Even if we begin thinking about X within a fraction of a second of us deliberately thinking X, and the content of X therefore then exists in our mind as the content of a claim rather than as an aspect of reality, this isn't the end of our belief of X. That is, although we can think about X while not believing X, we can of course also think about X while believing X.

So why can it seem obvious that we won't start believing X simply by deliberately thinking X? Consider again the example of believing that David isn’t vegetarian and then deliberately thinking 'David is vegetarian'.

Immediately after deliberately thinking 'David is vegetarian', and thereby believing this claim, we’ll be aware that we believed the opposite immediately before doing so, and that we were thinking 'David is vegetarian' just then only because we decided to say to ourself this claim that we didn't believe. And so we’ll then conclude 'David isn't vegetarian'.

And given the simplicity of this reasoning, and the brain's speediness, it'll occur within a fraction of a second of us deliberately thinking 'David is vegetarian'. So our belief that David is vegetarian will only last a fraction of a second, and we'll therefore normally have no awareness of it.

And the same applies whenever we deliberately think a claim that's contrary to what we believed immediately before doing so.

We may also deliberately think, and thereby believe, claim X when we don't already hold a belief on the subject of X. Immediately after doing so we’ll be aware that we didn’t hold a belief on the subject of X immediately before doing so, and that we were thinking X just then only because we decided to say to ourself this claim that we didn't believe. And so we’ll then conclude that we're ignorant about the truth of X, with this belief therefore replacing our belief of X.

And given the simplicity of this reasoning, and the brain's speediness, it'll occur within a fraction of a second of us deliberately thinking X. So our belief of X will only last a fraction of a second, and we'll therefore normally have no awareness of it.

We may even deliberately think, and thereby believe, claim X when we already believe X – and our belief of X upon and just after doing so will seem to be due to our prior belief of X.

The critical point from the analysis so far is that however we come to be thinking claim X, doing so is always the mental state of believing X. Now consider the entrance of a claim into our mind.

The entrance of a claim into our mind

Again, a claim enters our mind via one of four cognitive processes:

• comprehension – when the claim is communicated to us via some medium that we perceive, which is normally voice or text

• reason – when the claim is a conclusion

• imagination – when we generate the claim without using reason

• recollection – when we retrieve the claim from our memory.

And if claim X exists in our mind we must be either thinking X or thinking about X, given that there’s no other possibility. So the entrance of X into our mind must consist of us either thinking X or thinking about X. But consider the latter possibility.

Thinking about X involves either contemplating X or thinking a claim concerning X. For example, thinking about the claim David is vegetarian involves either contemplating this claim or thinking a claim such as The claim 'David is vegetarian' is false or Amy said that David is vegetarian.

However, I'm concerned here with X entering our mind by itself, upon being comprehended, concluded, imagined-up or recalled. So the question of whether that entrance consists of us thinking X or thinking about X only concerns thinking about X in the sense of contemplating X – which is the sense that I mean when I subsequently refer to thinking about X, except when I'm explicitly referring to thinking a claim concerning X.

Regarding the process of comprehending claim X, it might be thought that this whole process involves, by definition, thinking about this claim that we're trying to comprehend. But this process involves our sense organs collecting information about whatever medium is communicating X, and then the sensory and language areas of our brain analysing that information in order to determine X. So we're unable to think about X until it has been produced by this process. During that process we can only think about X in the sense of thinking about the existence of this claim that we’re trying to comprehend.

Of course, when we’re part-way through comprehending X we can think about the part of X that we’ve comprehended so far. But thinking about X as a whole – in the sense that doesn’t just involve thinking about the existence of X, but involves X existing in our mind – obviously requires us to have comprehended the whole of X.

Regardless of the process by which claim X enters our mind, thinking about X is a further cognitive process.

Any kind of process involves the processing of the input, or inputs, to the process, which produces an output:

In the case of the process of book manufacturing, the inputs include paper and ink, and the output is, of course, a book. In the case of the cognitive process of thinking about claim X, X is obviously the main input to this process. The other inputs include things stored in our memory that are related to this claim. And any output of this process is thought Y about X, whether Y is generated by our reason or imagination, or is recalled.

And an input to a process can of course be the output of another process:

In the case of book manufacturing, the paper and ink are the outputs of other processes. In the case of thinking about X, X is the output of the cognitive process of either comprehension, reason, imagination or recollection:

And the outputting of X from that first process is by definition the entrance of X into our mind. That is, the completion of the cognitive process of comprehending, concluding, imagining-up or recalling X is by definition the entrance of X into our mind.

It's possible that upon X being determined by the process of comprehension, or generated by the process of reason or imagination, or retrieved from our memory by the process of recollection, it must then be transmitted to some central processing area of the brain in order to enter the mind. If so, that transmission of X to this area will itself be a process.

But this process will be the final sub-process of the first process, given that the completion of the first process is by definition the entrance of X into our mind. That is, the outputting of X from the first process will be the arrival of X in this central processing area.

The fact that the outputting of X from the first process is the entrance of X into our mind means that in order for that entrance to consist of us thinking about X – that is, in order for it to be the entrance of X into the process of thinking about X – the outputting of X from the first process must also be the inputting of X into the process of thinking about X. That is, the outputting of X from the first process, and the inputting of X into the process of thinking about X, must be different perspectives of the same event. However, they actually can't ever be the same event.

The outputting of X from the first process is the completion of an occurrence of that process, and so involves this occurrence of the process stopping. And the inputting of X into the process of thinking about X is the beginning of an occurrence of that process, and so involves this occurrence of the process starting. And a process starting is obviously a different kind of event from a process stopping – indeed, they're opposite kinds of events. And, by definition, different kinds of events can't ever be the same event.

So the inputting of X into the process of thinking about X must always occur after the outputting of X from the first process, although possibly immediately after.

This logic applies whenever the output of one process is an input to a second. That is, the outputting of something from one process, and the inputting of that thing into a second process, are inherently different kinds of events, and so can't ever be same event, regardless of the processes involved. And so that inputting must always occur after that outputting.

Indeed, the mere fact that we can conceive of a time gap between these two events implies that they're inherently different kinds of events, and so can't ever be the same event, regardless of the processes involved. That is, the concept of a time gap between these two events involves this outputting of something from a process, and this inputting of the same thing into a process, each occurring without involving, in themselves, the other – which implies, by definition, that they're different kinds of events.

The conclusion that the outputting of something from one process, and the inputting of that thing into a second process, can't ever be the same event might be objected to as follows

Imagine two adjacent rooms connected by an open doorway, and someone walking continuously from the middle of the first room to the middle of the second via this doorway. This person exiting the first room, as they pass through the doorway, is also them entering the second room. That is, even though exiting and entering are conceptual opposites, this person exiting the first room, and them entering the second, are different perspectives of the same event – them passing through the doorway – rather than consecutive events.

And this person exiting the first room is the outputting of them from that room, and them entering the second room is the inputting of them into that room. So outputting and inputting can be the same event.

However, given that outputting is by definition the completion of the production of something by a process, something is outputted from a process. And given that inputting is by definition the beginning of the processing of something, something is inputted into a process. So the idea of something being outputted from, or inputted into, a room is actually nonsensical.

This person's journey involves them walking from the middle of the first room to the doorway, and then from the doorway to the middle of the second room. And walking from one location to another is a process. But given that they walk continuously from the middle of the first room to the middle of the second via this open doorway their journey constitutes not two consecutive processes but one process.

By definition, a process ending involves the relevant activity stopping, and a process beginning involves the relevant activity starting. So the person's journey from the middle of the first room to the doorway, and then from the doorway to the middle of the second room, could only constitute two consecutive processes if their walking stopped and then restarted at the doorway.

So instead of referring to the person's walking from the middle of the first room to the doorway as the process of them walking from the middle of the first room to the doorway, we should refer to it as being part of the process of them walking from the middle of the first room to the middle of the second.

Therefore, whereas outputting and inputting being the same event would involve two processes, this person exiting the first room being the same event as them entering the second room involves only one process. That is, that exiting and entering occurs during a process, and the same process, rather than, respectively, at the completion of one process and the beginning of another.

Also, given that the outputting of something from a process is the end point of that process, and the inputting of something into a process is the beginning of the processing of that thing, they both occur in an instant. But given that the simultaneous exiting of the person from the first room and their entering the second is them crossing the doorway threshold, this doesn't occur in an instant. That is, it begins when some part of their body first crosses the threshold, and ends when all of their body has crossed the threshold.

It might be thought that if the person's walking across the threshold occurs over a period of time, rather than in an instant, then it can be referred to as the process of them walking across the threshold. But it could only constitute this process if their walking started with some part of their body first crossing the threshold, and ended when all of their body had crossed the threshold. As with the person's walking from the middle of the first room to the doorway, we should instead refer to this walking as being part of the process of them walking from the middle of the first room to the middle of the second.

So this objection fails to disprove the conclusion that the outputting of something from one process, and the inputting of that thing into a second process, can't ever be the same event.

So the outputting of claim X from the first process indeed can’t ever also be the inputting of X into the process of thinking about X. And, again, the outputting of X from the first process is by definition the entrance of X into our mind. So the entrance of X into our mind via any cognitive process can't itself ever consist of us thinking about X.

It might then be objected that the cognitive activity involved in comprehending, concluding, imagining-up or recalling X could actually involve not just the first process – the process that determines, generates or retrieves X – but also the process of thinking about X.

That is, the first process and the process of thinking about X could actually be consecutive sub-processes of the process of comprehending, concluding, imagining-up or recalling X. And if the completion of this process involves the sub-process of thinking about X, then the entrance of X into our mind via any cognitive process actually always consists of us thinking about X.

However, consider comprehending a claim, and consider that this is a cognitive task.

The performance of any kind of task – whether by our mind alone, or our mind and body, or a machine – is a whole process. That is, the beginning of the performance of a task is the beginning of a process, and the completion of the task is the completion of that process, with the goal of the task being the output of the process.

The performance of a task may involve the performance of sub-tasks, with such activities therefore being sub-processes. And that task may itself be a sub-task, with the performance of the task therefore itself being a sub-process. But the performance of a task is a whole process even if that process involves sub-processes or is a sub-process, or both.

So the performance of the cognitive task of comprehending a claim is a whole cognitive process. Indeed, we refer to 'the process of comprehending a claim'.

But, again, the completion of the cognitive process of comprehending claim X is by definition the entrance of X into our mind. And, by definition, X exists in our mind from the beginning of the process of thinking about X. So if the process of comprehending X involved both the first process and the process of thinking about X it would actually only involve the first moment of the latter process. That is, the beginning of the process of thinking about X would also be the completion of the process of comprehending X.

And although a process can consist of two consecutive sub-processes, one process and just the beginning of another process don't together constitute a whole process. That is, the completion of a process is by definition a process ending, not beginning – it involves outputting, not inputting. So the completion of the process of comprehending X can't even be the beginning of the process of thinking about X.

Therefore the process of comprehending X can't involve both the first process and the process of thinking about X, and so must indeed be simply the first process. And the same logic applies to concluding, imagining-up or recalling a claim.

So the entrance of X into our mind via any cognitive process indeed can't itself ever consist of us thinking about X. Although, the brain's speediness means that we can begin thinking about X within a fraction of a second of X entering our mind, and so it can seem that we were doing so upon X entering our mind.

Therefore the entrance of X into our mind via any cognitive process must always consist of us thinking X, given that there’s no other possibility.

Indeed, the above analysis regarding thinking about X doesn't similarly apply to thinking X. That analysis shows that the entrance of X into our mind can't consist of us thinking about X because thinking about X is a cognitive process that can only begin after the completion of the cognitive process by which X enters our mind. But thinking X is a specific thought, and a specific thought is not a cognitive process but the output of a cognitive process – which aligns with the entrance of X into our mind being the output of a cognitive process.

Concluding X consists by definition of us thinking X. But comprehending, imagining-up or recalling X can seem to consist of us thinking about X. However, again, this is an illusion due to the brain's speediness.

It might be objected that even if the outputting of something from one process, and the inputting of that thing into a second process, are different kinds of events, and so by definition can't ever be the same event, different events can be simultaneous, and so that outputting and inputting can be simultaneous. Therefore it's still possible for the process of thinking about claim X to begin upon X entering our mind. But this objection also fails.

It's indeed possible for the outputting of something from one process, and the inputting of that thing into a second process, to be simultaneous. 

For example, imagine a litre of water being poured into an empty electric kettle, and the kettle's heating element beginning to heat the water at the same moment that the transfer of the water is completed. The output of the process of transferring the litre of water to the kettle is that water being located in the kettle. And that water being located in the kettle is obviously also an input to the process of heating that water – the other input being the electricity powering the kettle.

So the outputting from the first process – the completion of this process – is the completion of the pouring of the litre of water into the kettle. And the simultaneous inputting of that litre of water into the second process – the beginning of this process – is the beginning of the heating of that water by the kettle's heating element. Therefore, even though the outputting of the water from the first process, and the inputting of that water into the second process, are different kinds of events, they're simultaneous.

However, given that the outputting of claim X from the first process is a different event from the inputting of X into the process of thinking about X, and is by definition in itself the entrance of X into our mind, which necessarily involves thinking X, we actually can't be thinking about X upon X entering our mind. That is, the outputting of X from the first process, and the inputting of X into the process of thinking about X, can't even be simultaneous – although, again, they can be immediately consecutive.

Indeed, given that the entrance of X into our mind is by definition the completion of the process of comprehending, concluding, imagining-up or recalling X, that entrance being the beginning of the process of thinking about X – which the above objection claims is possible – would actually constitute the completion of the first process being the beginning of the process of thinking about X – which, again, is impossible.

The fact that the entrance of X into our mind via any cognitive process always consists of us thinking X, together with the fact that thinking X is always the mental state of believing X, however we come to be thinking X, means that the entrance of X into our mind via any cognitive process is always the mental state of believing X.

And the analysis so far shows that our belief of X upon X entering our mind is due to merely that entrance, rather than the nature of the cognitive process by which X enters our mind. That is, that analysis shows that the entrance of X into our mind is the outputting of X from a cognitive process, and outputting can't also be inputting, and so the entrance of X into our mind can't also be the inputting of X into the cognitive process of thinking about X, and so must consist of us thinking X, which is always the mental state of believing X.

So the mere entrance of a claim into our mind, whether via comprehension, reason, imagination or recollection, causes us to believe it. I call this theory of belief formation credulism, given its extreme claim about our credulity.

And our belief of claim X upon it entering our mind continues beyond that entrance, due to the content of X being stored in our memory as an aspect of reality. Again, believing X doesn't necessarily involve currently thinking X.

Even if we begin thinking about X within a fraction of a second of X entering our mind, and the content of X therefore then exists in our mind as the content of X rather than as an aspect of reality, this isn't the end of our belief of X. Again, although we can think about X while not believing X, we can also think about X while believing X.

Again, credulism can seem obviously wrong – which can itself seem to disprove it. It can seem obvious from experience that merely comprehending, imagining-up or recalling a claim doesn't cause us to believe it. Regarding reason, a conclusion is by definition a belief. But credulism implies that our belief of this claim upon it entering our mind is due merely to that entrance, rather than being due to the claim being the product of our reason. And that can seem obviously contrary to both the concept and experience of reasoning.

But consider, first, comprehending a claim.

Credulism and comprehending a claim

It can seem obvious from experience that merely comprehending the claim London is the capital of France, for example, doesn't cause us to wrongly believe that London is the capital of France. Indeed, it can seem obvious that we just then instead merely immediately thought 'London isn't the capital of France'.

However, given that this thought was a response to the comprehended claim, it must have occurred immediately after we comprehended that claim. So this immediate thought actually doesn't in itself mean that we didn't believe the comprehended claim upon comprehending it.

The claim London is the capital of France is obviously incompatible with the set of mutually compatible beliefs of ours that are relevant to the claim – which includes the beliefs A country's capital is located in that country, London is located in England, England and France are different countries, London is the capital of, and only of, England and the United Kingdom, Paris is located in France and Paris is the capital of France.

And the obviousness of this incompatibility means, by definition, that our awareness of it required very little thinking – as did our subsequent conclusion, based on that incompatibility, that London isn't the capital of France, and that the claim London is the capital of France is therefore false. Also, again, the brain functions on the timescale of milliseconds.

So our belief of the claim London is the capital of France only lasted the fraction of a second that it took us to think/believe 'London isn't the capital of France'. And the extreme briefness of this belief means that we've no awareness of both it and our credulity. Hence our sense that the entrance of this claim into our mind upon comprehending it didn't cause us to believe it.

And the same applies to our comprehension of any claim that immediately seems false.

That includes the theory of credulism itself. Again, the fact that credulism can seem obviously wrong can itself seem to disprove it. But we in reality do believe it upon comprehending it. However, its apparent obvious falseness means that this belief only lasts the fraction of a second that it takes us to conclude that the mere entrance of a claim into our mind doesn't cause us to believe it.

The above analysis similarly applies to our comprehension of claims that immediately seem uncertain.

For example, if we hear someone declare that it'll rain on Friday next week this claim will likely immediately seem uncertain, given the uncertainty inherent in weather forecasts and the increasing probability of them being wrong the further in the future they refer to. But even if the claim does immediately seem uncertain we'll actually believe it upon comprehending it. However, this belief will only last the fraction of a second that it takes us to conclude that it's uncertain that it'll rain on Friday next week. And the extreme briefness of our belief means that we'll have no awareness of both it and our credulity.

We also comprehend claims that don't immediately seem false or uncertain, but which we didn't already believe. For example, if we don't hold any beliefs about David's dietary choices, and then hear someone say that he's vegetarian, we may not immediately think of a reason to disbelieve or even doubt this, especially if we don't know anything about David. If so, our belief of this claim upon comprehending it won't be replaced by a contrary belief within a fraction of a second of forming.

But although our belief of such a claim upon comprehending it can therefore last long enough for us to be able to be aware of both it and our credulity, we tend not to be even in such cases.

Being aware of our belief of claim X involves, by definition, thinking about our belief of X, which involves thinking about X. So, given the difference between thinking X and thinking about X, although thinking/believing X constitutes this belief being involved in our thinking, it doesn't in itself actually involve being aware of this belief.

For example, although thinking/believing ‘David is vegetarian’ constitutes this belief being involved in our thinking, it doesn’t in itself actually involve being aware of this belief. That is, it involves, in itself, thinking about David, and him being vegetarian, without thinking about ourselves and our belief that David is vegetarian.

Just as, given the difference between thinking claim X and thinking about X, a claim can exist in our mind without us thinking about it, a belief can exist in our mind without us thinking about it, because we can think about the content of the belief without thinking about our belief of that content. Indeed, thinking X involves both a claim and a belief existing in our mind without us thinking about them.

If we're thinking about our belief of claim X while apparently thinking/believing X then we're actually not at that moment thinking/believing X. Although, given the brain's speediness, we may think about our belief of X so soon before or after thinking/believing X that our thinking/believing X can seem to in itself involve thinking about this belief.

So when we comprehend a claim that doesn't immediately seem false or uncertain, but which we didn't already believe, we can't be aware of our belief of this claim upon comprehending/thinking it and whenever we're subsequently thinking/believing it.

Of course, we can think about, and so be aware of, this belief when we're not thinking/believing the claim. But we tend not to, for several reasons.

First, our absence of uncertainty in the claim means that we tend not to be motivated to question, and thereby think about, this belief. That is, our absence of uncertainty means that we tend to think about the content of the belief but not our belief of that content.

Also, we’re usually too cognitively busy thinking about the content of our beliefs, including trying to make inferences from that content, to think about our belief of that content.

Our minimum waking cognitive activity involves continuously trying to work-out:

• what's happening in the immediate present, often including what's happening in other people’s minds

• why it's happening

• what's likely to happen in the immediate future, often including what's likely to happen in other people’s minds

• what should be our goals for the immediate future, taking into account our longer-term goals

• how best to act in the immediate future in order to achieve our immediate goals, often including how best to interact with other people.

This cognitive activity involves a constant stream of belief formation. And, again, it's our minimum waking cognitive activity.

And our degree of cognitive busyness increases as the following factors increase:

• time pressure

• the quantity of information being processed

• the difficulty of the current cognitive task – which increases as stress, tiredness or distraction increases

• the number of cognitive tasks being performed in parallel.

We can sometimes be so cognitively busy that even when we comprehend a claim that would normally immediately seem false or uncertain our belief of it isn't replaced by a contrary belief within a fraction of a second of forming, and can last until our level of cognitive busyness has reduced to normal.

Also, the less important it is to us whether a believed claim is indeed true, the less likely we are to be motivated to question, and thereby think about, our belief of it. And for many of our beliefs the actual truth of the believed claim isn't that important to us – as could be the case in the above example of our belief that David is vegetarian, after hearing someone state this.

So, for all of these reasons, even when our belief of a comprehended claim that we didn't already believe lasts long enough for us to be able to be aware of it, we tend not to be. And we of course can't be aware of our credulity in the formation of this belief if we aren't aware of the belief.

Also, even when we're aware of the belief, our absence of uncertainty means that we tend not to be motivated to question how it formed, and we're usually too cognitively busy to think about how it formed. Also, the less important it is to us whether the believed claim is indeed true, the less likely we are to be motivated to question how the belief formed.

Also, generally, the more time that has passed since the belief formed the less likely we are to think about this event. And even when we cease holding the belief, and then think about our past belief of this claim that we now consider false or uncertain, we won’t necessarily think about how it formed.

And we of course can't be aware of our credulity in the formation of the belief if we’re aware of the belief but don't think about how it formed.

And even if we do consider the formation of the belief – whether or not we still hold it – we may not remember that it formed upon us hearing or reading the claim concerned. And even if we do remember this we can assume that the belief formed just after our comprehension of the claim, whether via reason or intuition.

To summarise the main conclusions of the analysis in this section so far, when we comprehend a claim that we didn't already believe, our resulting belief of it either only lasts a fraction of a second – if the claim immediately seems false or uncertain – and so we have no awareness of the belief, or the belief lasts long enough for us to be able to be aware of both it and our credulity, but even then we tend not to be aware of that credulity, or even the belief.

And in the case of comprehending a claim that we did already believe, we can of course attribute our belief of it upon doing so, and subsequently, to our prior belief of it.

We're therefore only occasionally aware of our credulity upon hearing or reading a claim. Hence, credulism can seem obviously contrary to our overall experience of comprehending claims, even though closer analysis reveals that it isn't.

It might be objected that it's both true by definition and obvious from experience that if we comprehend a claim that we didn't already believe, then our level of trust in the claim's source on the subject of the claim affects whether we believe the claim, contrary to credulism.

But, again, if we're aware that one of our beliefs, past or present, formed upon us hearing or reading the claim concerned, we can assume that it formed just after our comprehension of the claim, whether via reason or intuition. So we can sometimes assume that the belief was the product of our consideration, just after comprehending the claim, of the trustworthiness of the claim’s source on the subject of the claim – whether or not such a consideration occurred, and, if it did, whether or not we recall it.

Also, if we comprehend a claim, X, that we didn’t already believe, and we distrust its source on the subject of X, then, given the brain's speediness, our resulting belief of X will only last the fraction of a second it takes us to conclude a contrary claim, such as It's uncertain whether X, or It's unlikely that X, or X is false, depending on the context and our level of distrust. And the extreme briefness of our belief of X means that we’ll have no awareness of it. So it can then seem that our distrust of X’s source on the subject of X prevented our belief of X.

It’s indeed true by definition that if we comprehend a claim that we didn't already believe, then our level of trust in the claim's source on the subject of the claim affects whether we believe the claim – but only after we comprehend/believe it. That is, it only affects whether we continue to believe the claim.

Although, there are two scenarios in which we comprehend a claim, X, that we didn’t already believe and our trust in X’s source on the subject of X leads to our belief of X in a way that isn't contrary to credulism.

The first is when that trust led us to pay attention to, or consult, that source, which then led to our comprehension/belief of X.

But such trust can even lead to our belief of X after we've comprehended X. That is, if after comprehending/believing X we cease believing X for some reason, we may subsequently either remember that we trust X’s source or develop such trust, and that trust may then lead us to conclude X.

Consider also our experience of other people comprehending claims.

We're by nature motivated to try to understand the world around us, which includes trying to understand other people. So we're by nature motivated to think about other people's beliefs, including how those beliefs formed. And this in turn means that we’re much more likely to be aware of other people’s credulity than they are, or than we are of our own credulity.

But if someone comprehends a claim that they didn’t already believe, and their resulting belief only lasts a fraction of a second, because the claim immediately seems to them false or uncertain, then not only will they not be aware of this belief, neither will we.

And even if the belief lasts long enough for us to be able to be aware of it, via what they say and do, we may not know or remember that it formed upon them comprehending the claim. And even if we do know and remember this we can assume that the belief formed just after their comprehension of the claim, via reason or intuition.

And in the case of someone comprehending a claim that we think, rightly or wrongly, they already believed, we can of course attribute their belief of it upon them doing so, and subsequently, to their prior belief of it.

So although we're much more often aware of other people’s credulity upon hearing or reading claims than we are of our own, we're still only occasionally aware of the former. And so credulism can seem obviously contrary to our overall experience of other people comprehending claims, even though closer analysis reveals that it isn't.

Not only is credulism not contrary to our experience of comprehending claims, and of other people comprehending claims, that experience is a source of evidence for credulism.

Imagine being at a social gathering but not currently talking to anyone, and then someone we've never previously met, and we know nothing about, approaches us with a smile and says 'Hi, I'm David'.

In this scenario this claim normally won't immediately seem false or even uncertain. So our resulting belief of it upon comprehending it normally won't be replaced by a contrary belief within a fraction of a second of forming. Therefore, according to credulism, we'll normally experience forming the belief that this person's name is David upon simply comprehending their claim that their name is David – which is indeed what we'd normally experience in this scenario.

So this familiar everyday experience of forming a belief upon simply comprehending a claim that doesn't immediately seem false or even uncertain is evidence for credulism that's hiding in plain sight.

Someone who thinks that credulism is false, or is simply unaware of the theory, might think that the formation of our belief that the person's name is David upon comprehending their claim is actually due to the fact that we've no reason to disbelieve or even doubt this claim.

But if that was true we'd experience first comprehending, but not believing, the claim, then deciding to assess whether their name is indeed David, then in turn deciding to assess whether there's any reason to disbelieve or even doubt it, then conducting this assessment, then concluding that there isn't such a reason, and then concluding that their name is indeed David.

Even taking into account the speediness of the brain, we couldn't undertake this chain of thinking between comprehending the claim and the formation of our belief of it without subsequently being aware that that thinking took place, and that our belief only formed upon its completion. And yet this belief formation normally doesn't involve this chain of thinking.

It might be objected that our normal experience of belief formation in this scenario actually isn't evidence for credulism. That is, what actually normally causes us to believe a communicated claim upon comprehending it is considering that the claim's source is trustworthy. In the above scenario, between first seeing the approaching person and them saying 'Hi, I'm David', we make a snap judgement, based on their appearance and manner, that they're trustworthy, and we thus believe this claim upon comprehending it.

But even if credulism was false, beliefs couldn't form in this way.

We never consider someone trustworthy regarding the truth of any claim they make about anything. That is, we only ever consider someone trustworthy regarding the truth of claims they make about particular subjects. And if the formation of our belief of comprehended claim X was due to our trust of X's source on the subject of X, we'd have needed to first determine that the subject of X is a subject that we trust the source to make true claims about, and then therefore conclude X.

But when, in the above scenario, we hear the person say 'Hi, I'm David' we don't normally experience first comprehending, but not believing, this claim, then considering that the subject of the claim is the speaker's name, and that this is a subject that we trust them to make true claims about, and then concluding that their name is indeed David. Again, we normally experience simply forming the belief that this person's name is David upon comprehending their claim that their name is David.

Another example of our experience of comprehending claims being a source of evidence for credulism is likely your experience of reading the following paragraph in the first section of this article:

And the first academic conference on Spinozan belief formation took place in 2018, in the US. Another is planned for 2026, in the Netherlands, where Spinoza was born.

That is, you likely experienced forming the belief that there's a conference on Spinozan belief formation planned for 2026, in the Netherlands, upon simply comprehending the content of the second sentence. But if you're interested in attending don't bother trying to find more information – I made-up this planned event just to provide this example. That is, just as you were likely experiencing significant doubt, or even disbelief, regarding Spinoza's theory, you were likely also experiencing evidence for it.

Now consider imagining-up or recalling a claim.

Credulism and imagining-up or recalling a claim

The analysis in the previous section similarly applies to imagining-up or recalling a claim.

So when we imagine-up or recall a claim that we didn't already believe, our resulting belief of it either only lasts a fraction of a second – if the claim immediately seems false or uncertain – and so we have no awareness of the belief, or the belief lasts long enough for us to be able to be aware of both it and our credulity, but even then we tend not to be aware of that credulity, or even the belief. And in the case of imagining-up or recalling a claim that we did already believe, we can of course attribute our belief of it upon doing so, and subsequently, to our prior belief of it.

We're therefore only occasionally aware of our credulity upon imagining-up or recalling a claim. Hence, credulism can seem obviously contrary to our overall experience of imagining-up or recalling claims, even though closer analysis reveals that it isn't.

Regarding imagining-up a claim, this is either deliberate or spontaneous. That is, a claim enters our mind via our imagination because either we decided to generate a claim with our imagination or our imagination spontaneously generated the claim. For example, the claim David is vegetarian can enter our mind via our imagination because we decided to use our imagination to generate a claim about David, but it can also do so because our imagination spontaneously generated this claim as we observed David eating a meat-free meal.

And in the case of deliberately imagining-up a claim that we didn't already believe, the fact that the entrance of the claim into our mind is immediately preceded by our effort to imagine-up a claim means that immediately after that entrance we'll be aware that the claim entered our mind just then as the product of our imagination.

So the claim will immediately seem uncertain for at least that reason, given that a claim generated by imagination is by definition a claim generated without using reason. Therefore, even if the claim doesn’t otherwise immediately seem uncertain, or immediately seem false, our belief of it will only last a fraction of a second, and so we’ll have no awareness of it.

But in the case of spontaneously imagining-up a claim that we didn't already believe, the fact that the entrance of the claim into our mind isn't immediately preceded by our effort to imagine-up a claim means that immediately after that entrance we won't necessarily be aware that the claim entered our mind just then as the product of our imagination. That is, we may only be thinking about this apparent aspect of reality, rather than also thinking about how the believed claim entered our mind.

So the claim won't necessarily immediately seem uncertain, and our belief of it therefore won't necessarily end within a fraction of a second of forming.

Regarding recalling a claim, this is similarly either deliberate or spontaneous. That is, we recall a claim because either we made an effort to do so or something triggered the recollection.

And in the case of deliberately recalling a claim that we didn't already believe, the fact that the entrance of the claim into our mind is immediately preceded by our effort to recall it means that immediately after that entrance we'll be aware that the entrance of the claim into our mind just then was us recalling it. But that awareness doesn't in itself give us reason to be uncertain about it.

This is obvious in the case of deliberately a claim that we did already believe – that is, deliberately recalling an apparent fact. Our awareness, immediately after the claim enters our mind, of why it did so is obviously not in itself reason to be uncertain about it.

But even in the case of deliberately recalling a claim that we didn't already believe, this awareness doesn't in itself give us reason to be uncertain about it. That is, whereas a claim generated by imagination is by definition a claim generated without using reason, the fact that a claim has just been retrieved from our memory doesn't in itself imply that it was originally generated, whether by us or someone else, without using reason.

Of course, the fact that a claim has just been retrieved from our memory also doesn't in itself imply that it was originally generated using reason. But our awareness of why it entered our mind just then doesn't in itself give us reason to think about how it was originally generated.

And in the case of spontaneously recalling a claim that we didn't already believe, we won't even necessarily be aware of why it entered our mind just then, as with spontaneously imagining-up such a claim.

So whether our recollection of a claim that we didn't already believe is deliberate or spontaneous the claim won't necessarily immediately seem uncertain, and our belief of it therefore won't necessarily end within a fraction of a second of forming.

Comprehending a claim is inherently deliberate. That is, it by definition involves a desire to obtain an understanding of the content of this claim that's being communicated to us via some medium that we're perceiving, which is normally voice or text.

And in the case of comprehending a claim that we didn't already believe, the fact that the entrance of the claim into our mind is immediately preceded by our effort to comprehend it means that immediately after that entrance we'll be aware that the entrance of the claim into our mind just then was us comprehending it. But, as with deliberately recalling a claim, that awareness doesn't in itself give us reason to be uncertain about it.

Consider also our experience of other people imagining-up or recalling claims. The analysis in the previous section again similarly applies. So although we're much more often aware of other people’s credulity upon imagining-up or recalling claims than we are of our own, we're still only occasionally aware of the former. And so credulism can seem obviously contrary to our overall experience of other people imagining-up or recalling claims, even though closer analysis reveals that it isn't.

In the previous section I also addressed the potential objection that it seems both true by definition and obvious from experience that if we comprehend a claim that we didn't already believe, then our level of trust in the claim's source on the subject of the claim affects whether we believe the claim, contrary to credulism. And the analysis countering this objection similarly applies to the same objection regarding recalling a claim that we didn’t already believe.

I've said that organically thinking X is when our thinking X is either a recollection of an apparent fact or a conclusion. But in reality comprehending X, imagining-up X, and recalling X when we didn’t already believe X, also involve organically thinking X. Whereas deliberately thinking X, like a silent mantra, by definition follows from thinking about X, organically thinking X doesn't.

Also, deliberately thinking X is always immediately preceded by organically thinking X, given that it's dependent on recalling this claim that we decided to think.

Now consider reason.

Credulism and reason

Again, although a conclusion is by definition a belief, credulism implies that our belief of this claim upon it entering our mind is due merely to that entrance, rather than being due to the claim being the product of our reason – which can seem obviously contrary to both the concept and experience of reasoning.

But consider first the concept of reasoning.

Reasoning involves determining an apparent logical implication of particular claims – the premises of our logic. For example, if we need to make a meal for David, and we learn that he's vegetarian, then our reasoning about what meal to make will probably begin with these two premises:

David is vegetarian

Vegetarians don’t eat meat

and we'll then determine the logical implication:

David doesn’t eat meat

which we’ll then probably consider along with the premise:

I shouldn't make a meal containing meat for someone who doesn’t eat meat

to determine the logical implication:

I shouldn't make a meal containing meat for David.

Although, given the brain's speediness, and the obviousness of these two logical steps, it can seem to us that we simply went straight from considering that David is vegetarian to concluding that we shouldn't make a meal containing meat for him.

We can of course determine an apparent logical implication of particular premises whether or not we actually believe those premises and the apparent logical implication of them. For example, we can determine that a logical implication of the premises All cats are green and All green things can fly is All cats can fly even though we disbelieve all three claims.

In the field of logic, a logical step is valid if the claim generated by it is indeed a logical implication of its premises, regardless of the truth of the premises and of that logical implication.

According to the prevailing understanding of reason, our belief of a claim upon it entering our mind as an apparent logical implication of particular premises is due to our belief not just of the validity of our logic, but also of those premises. That is, given that the premises exist in our mind as aspects of reality, a claim entering our mind as an apparent logical implication of them will naturally do so as an aspect of reality too.

This understanding of reason can seem true by definition and therefore irrefutable, but it's actually fatally logically flawed, even without consideration of credulism.

The process of determining an apparent logical implication of particular premises involves, by definition, thinking about the claims that are those premises. So this process necessarily involves the content of those claims existing in our mind as the content of claims. That is, even if we believe the premises, this process actually can't in itself involve their content existing in our mind as aspects of reality.

So even if we believe the premises this process actually merely involves, in itself, trying to determine a claim that's logically implied by those claims, rather than trying to determine an aspect of reality that's logically implied by other apparent aspects of reality. That is, although this process explains our belief that claim X is a logical implication of the claims that are the premises, it can’t by itself explain our belief of X upon X entering our mind via this process.

It might be thought that this merely means that the prevailing understanding of reason needs a relatively minor revision. That is, our belief of X actually forms immediately after X enters our mind, upon us considering our belief of the premises, and then concluding X. Given the brain's speediness, and the obviousness of this conclusion, it forms within a fraction of a second of X entering our mind – hence our sense that we believe X upon it entering our mind.

But this revised understanding of reason is also fatally logically flawed, given that our concluding X would by definition involve a further logical step. If our belief of the product of the original logical step was dependent on a second logical step, then our belief of the product of that second logical step would likewise be dependent on a third logical step, and so on indefinitely. So belief formation via reason would require an infinite number of logical steps, and would therefore be impossible.

The other problem with this revised understanding of reason is that, given credulism, it's unnecessary to conclude X, immediately after X enters our mind, in order to believe X.

Indeed, without knowledge of credulism it might be thought that the need for an infinite number of logical steps could have been overcome by the evolution of a cognitive mechanism that causes us to automatically form belief X immediately after X enters our mind as a logical implication of premises that we believe. But given credulism there was no need for such a mechanism to evolve.

In sum, although credulism is indeed contrary to the current conception of reasoning, it's that conception that's wrong. And there’s no reason to think that this conception can’t be replaced by one that incorporates the idea that the mere entrance of a claim into our mind causes us to believe it. Indeed, as I've shown, there's reason to think that the current conception must be replaced by this new conception.

When we form a conclusion our belief of our premises was obviously necessary for us to use them as the basis of our reasoning. And our belief of the validity of our logic was obviously necessary for us to apply it to those premises. And the application of that logic to those premises is obviously what led to the entrance into our mind of the claim that we thereby believed.

But our belief of that claim upon it entering our mind isn't due to our belief of our premises and of the validity of our logic. That is, it isn't due to the claim being the product of our reason. It's due merely to the entrance of the claim into our mind upon being produced by our reason. So our reasoning leads to, but doesn't itself cause, our belief of the claim. In other words, although to conclude claim X is by definition to believe X, it isn't the case that belief X forms because we've concluded X – instead, we conclude/believe X because X entered our mind.

Regardless of the theory of belief formation, to conclude X is by definition to form belief X upon determining that X is a logical implication of particular premises that we believe. And according to the current conception of reasoning, to conclude X is to logically determine this apparent aspect of reality from particular other apparent aspects of reality. But in reality to conclude X is to logically determine claim X from particular claims that we believe, and thereby form belief X given credulism.

Now consider our experience of reasoning.

Again, it can seem obvious from our experience of forming a conclusion that our belief of this claim upon it entering our mind is due to it being the product of our reason.

But our experience of forming a conclusion would actually be the same whether this belief formation is due to the claim being the product of our reason or the mere entrance of the claim into our mind upon being produced by that reason. That is, either way this experience would consist of us forming a belief of the claim upon it entering our mind via reason.

So credulism actually isn't contrary to our experience of reasoning. When we form a conclusion our sense that our belief of this claim upon it entering our mind was due to it being the product of our reason is actually merely our interpretation of this experience, based on the current conception of reasoning.

And the same applies to our experience of other people forming beliefs via reason. This experience would be the same whether this belief formation is due to the claim being the product of the person’s reason or to the mere entrance of the claim into their mind upon being produced by that reason. When we observe someone forming a conclusion our sense that their belief of this claim upon it entering their mind was due to it being the product of their reason is actually merely our interpretation of this observation, based on the current conception of reasoning.

It might be thought that there are some scenarios in which credulism is definitely contrary to our experience of reasoning.

Although a conclusion is by definition a claim that has entered our mind via reason, there are some occasions when a claim that enters our mind via reason isn't a conclusion.

Again, to conclude X is by definition to form belief X upon determining that X is a logical implication of particular premises that we believe.

But we sometimes generate a claim via logic that we believe is flawed or questionable. For example, we deliberately apply apparently flawed or questionable logic to particular premises in order to illustrate such logic.

Also, we sometimes generate a claim via logic that’s based on premises that we either disbelieve or are uncertain about. For example, we determine apparent logical implications of premises that we either disbelieve or are uncertain about when undertaking hypothetical, 'What if...', reasoning.

In such cases, our belief about the validity or premises of the logic that we use to generate claim X means that the entrance of X into our mind doesn't constitute us concluding X. That is, the conclusion of our reasoning isn't simply X, but a claim of either the form X is an illogical [or possibly illogical] inference from the premises or the form X is a logical implication of the false [or uncertain] premises. The premises of this conclusion aren't the premises of the logic that we use to generate claim X, but our belief that claim X is generated by that logic, and our belief about the validity or premises of that logic.

But in such cases X does first enter our mind by itself, upon being generated. Indeed, by definition, the cognitive process of generating the claim about X involves thinking about X, which involves X existing in our mind by itself. And credulism implies that we believe X upon it entering our mind by itself. However, the idea that we form belief X during such reasoning, despite our belief about the validity or premises of the logic that we used to generate X, can seem obviously contrary to our experience of such reasoning.

But given the brain's speediness, and our belief about the validity or premises of the logic that we used to generate X, our belief of X upon it entering our mind only lasts the fraction of a second that it takes us to conclude X is uncertain. And the extreme briefness of our belief of X means that we've no awareness of it.

An exception to credulism?

It might be thought that even if all of the analysis so far is sound there are still some scenarios in which the mere entrance of a claim into our mind doesn't cause us to believe it.

Consider a claim, Y, which refers to claim X, such as The claim 'David is vegetarian' is true or Amy said that David is vegetarian.

As I said in the previous section, by definition, the cognitive process of generating a claim about X with our reason involves thinking about X, which involves X existing in our mind by itself. And credulism implies that we believe X upon it entering our mind by itself. And the same applies to generating Y with our imagination.

But consider comprehending or recalling Y, which don't in themselves involve us generating this claim about X. Although the entrance of Y into our mind in each case involves us thinking/believing Y, thinking Y is thinking about X rather than thinking X. So it might be thought that the entrance of X into our mind when we comprehend or recall Y doesn't cause us to believe X.

However, even in these two scenarios the entrance of X into our mind does cause us to believe X.

Given that X is part of Y we comprehend X as part of comprehending Y, and recall X as part of recalling Y. And so X enters our mind by itself during these processes too, which involves us thinking/believing X. Although, given the brain's speediness, Y can enter our mind within a fraction of a second of X doing so, and so these two mental events can seem to be the same event.

In the case of comprehending or recalling the claim The claim 'David is vegetarian' is false, we'll first believe the claim David is vegetarian, but then believe, within a fraction of a second, that this claim is false, and so then conclude, within a further fraction of a second, that David isn't vegetarian.

It might be thought that if X is the last part of Y – as in Amy said that David is vegetarian – comprehending X, after comprehending the preceding part of Y, constitutes comprehending Y. But, in such cases, comprehending Y is actually dependent on us subsequently combining our comprehension of X with our comprehension of the preceding part. Although, again, our comprehension of Y will occur within a fraction of a second of our comprehension of X, and so these two mental events can seem to be the same event. And the same applies to recalling Y.

Even if we used our imagination to generate the claim Amy said that David is vegetarian not by first considering the claim David is vegetarian, but by creating the word string Amy said that David is vegetarian by generating each word in turn, the two claims wouldn't enter our mind simultaneously upon the last word, vegetarian, entering our mind.

That is, given that the claim David is vegetarian is part of the claim Amy said that David is vegetarian, our understanding that we'd generated the claim Amy said that David is vegetarian would be dependent on, and so preceded by, our understanding that we'd generated the claim David is vegetarian.

The logical necessity of credulism

The argument I presented for credulism actually has a highly counterintuitive conclusion in two ways. The argument consists entirely of conceptual analysis – that is, it doesn't at any point depend on observational evidence. It therefore reveals not only that the mere entrance of a claim into our mind via any cognitive process causes us to believe it, but also that this is due not to the nature of the human brain but simply logical necessity.

The central tenet of the field of psychology today is that how the human mind works is ultimately due solely to the wiring and chemistry of the human brain, which are in turn determined by a person’s genes and experiences. But although our capacity for belief is obviously due to the nature of the human brain – as is our capacity for reason, emotion, language, perception, and so on – our extreme credulity isn't. Instead, that extreme credulity is simply a logically necessary aspect of a claim entering the mind – and not just the human mind, but the mind of any intelligent entity.

At the dawn of modern science in the 16th and 17th centuries using mathematics to develop theories, as opposed to using mathematics simply to describe and predict the world in a way that's compatible with current theories, was controversial. Such reliance on abstract reasoning rather than observation was considered unscientific by most scholars. But in science today it's accepted as a legitimate form of theoretical research. This is particularly evident in theoretical physics, which relies heavily on mathematics.

A prominent early example of this shift is Nicolaus Copernicus's development, in the early 16th century, of the theory that the Earth goes around the Sun, rather than vice versa. His theory wasn't based on new or more precise astronomical observations, but instead arose from a desire for an explanation of planetary motions in the night sky with greater mathematical harmony and simplicity.

Another famous illustration of the importance of mathematics in the development of scientific theories is Albert Einstein's two theories of relativity – special and general relativity. Starting with some well-established observations, he reached his radical conclusions about space, time, matter and gravity via chains of logic and mathematics that don't at any subsequent point refer to observational evidence.

Similarly, the logical necessity of credulism shows that using logic alone to develop theories about human psychology is scientifically legitimate, even though it's currently almost universally considered unscientific by scientists. Indeed, the logical necessity of credulism means that using logic alone is the only way of fully understanding belief formation. That is, although we could find observational evidence for credulism by studying brain activity, no amount of such evidence could show the logical necessity of credulism.

I explained in the previous article that the idea that the formation of belief X is us assessing that claim X is true is fatally logically flawed. And at the end of that article I raised an alternative conception of belief formation. The formation of belief X is us concluding X – however brief, irrational, emotional, credulous or intuitive our reasoning is. As I explained, even the formation of beliefs about our surroundings or body via sensory perception requires reason. However, this conception is also fatally logically flawed. 

If it was true then the formation of belief X would be dependent on X entering our mind via reason. But, by logical necessity, the mere entrance of a claim into our mind via any cognitive process – comprehension, reason, imagination or recollection – causes us to believe it. So, by logical necessity, the formation of belief X is actually dependent on X merely entering our mind, rather than on it doing so specifically via reason. That is, by logical necessity, the formation of believe X is actually simply X entering our mind, via any cognitive process.

Why didn't we evolve into almost constant liars?

It might be thought that if credulism is logically inevitable for every member of our species then that should create a very strong evolutionary pressure towards telling lies that benefit us when believed by others – so strong that it should have resulted in us all being almost constant liars. And yet most people are far from being this dishonest. So credulism can't be logically necessary. However, this reasoning is flawed.

As I showed in the section on credulism and comprehending claims, our belief of a claim upon comprehending it isn't necessarily indefinite, and may only last a fraction of a second. That is, even the extreme credulity of credulism isn't complete credulity. So credulism doesn't imply that we can't disbelieve a comprehended claim, and that lies therefore can't be recognised as such, which is obviously false.

We therefore usually only lie when we think that it won't be obvious that we're lying. But even if a lie is indeed not immediately recognised as such, it'll often be found-out eventually, whether it takes minutes, hours, days, weeks, months or years, and whether it's first found-out by the person or people lied to or by someone else.

Also, generally, the more often we lie the more often our lies will be recognised as such, partly simply because there are more opportunities for our lies to be recognised as such, but also because it becomes harder to remember all of our lies and so ensure that they don't contradict each other.

Also, when we become aware that we've been lied to, or that someone else has been, we naturally tend to be motivated to tell others about it, whether to complain or warn or both – especially when we believe that the lie was motivated by self-interest.

And knowledge of a lie will naturally tend to reduce how trusted the liar is to be honest. In the case of a lie that was apparently motivated by self-interest, knowledge of it will also tend to reduce how moral the liar is perceived to be. This reputational damage will naturally then tend to negatively impact their life, whether or not they're aware of every way in which it does, or are even aware of the reputational damage, or to whom their lie has become known. And the more people that know about the lie the greater the negative impact tends to be.

This negative impact is often as great, or greater, than any positive impact on the liar of their lie being believed. Also, the lie being found-out can mean that a particular positive impact of the lie on the liar is actually reversed. For example, if someone gets a job partly by lying, but the employer discovers the lie, then the person could lose the job. In such cases, the effect of the lie is ultimately all cost and no benefit to the liar. Likewise, if a lie is immediately recognised as such by the person or people being lied to then the effect of the lie is all cost and no benefit to the liar.

Also, we evolved living in hunter-gatherer groups of only a few dozen individuals. So we evolved in a social environment in which knowledge of a lie would have likely quickly spread to all, or at least almost all, of those the liar interacted with, and depended on, in their daily life. Therefore the reputational damage that tends to result from a lie being found-out would have tended to have an even greater negative impact on the liar during this period than it tends to today.

So the idea that the logical inevitability of credulism implies that we should have evolved into almost constant liars, contrary to reality, is false.

However, that logical inevitability will have created a very strong evolutionary pressure towards telling lies. But specifically lies that benefit us when believed by others, and which either aren't found-out or, if they are, still benefit us overall. That is, it will have led to the evolution of us having a desire to tell lies that we're confident, to at least some particular degree, will not only benefit us if believed by others, but also either not be found-out or, if they are, still benefit us overall.

This desire competes with other desires in each particular situation, such as a desire to act morally. But it will sometimes overcome those contrary desires, and so explains why we sometimes tell lies that we're confident will benefit us when believed by others, despite such lies often costing us overall.

Vindicating Spinoza

Again, this theory of belief formation was first proposed by the prominent 17th-century philosopher Baruch Spinoza, in his posthumous 1677 book Ethics.

However, the argument for credulism that I've presented in this article isn’t actually Spinoza’s, but was developed by me. Spinoza presented an obscure philosophical argument that at one point refers to the geometry of a triangle, and at another point refers to an imaginary winged horse. I'm not a philosopher, and am unable to follow it. But even a philosopher I contacted who's an expert on Spinoza's works admitted that they didn't understand this particular argument, and also wasn't aware of any writings which attempted an explanation of it.

The obscurity of Spinoza’s argument, together with its highly counterintuitive conclusion, explains why support for his theory has been very low since it was published.

The most prominent scholarship on the theory is a 1991 paper called ‘How Mental Systems Believe’, by Harvard psychology professor Daniel Gilbert, one of the few academics who support the theory. It catalogues apparent supporting observational evidence, including experimental evidence, which I’ll review in an upcoming article in this series, along with more recent apparent supporting observational evidence. For example, as I mentioned earlier, a 2022 paper by neuroscientists at Harvard, Princeton and Dartmouth universities presents brain scan evidence which seems to support the theory.

However, Gilbert's paper misrepresents Spinoza’s theory in one significant way. It only refers to the theory as applying to the entrance of claims into our mind via comprehension.

This is also true of most other writings which refer to the theory. And in most cases it seems likely that this is because the author based their understanding of the theory on either Gilbert’s paper or a writing by someone who based their understanding of the theory on Gilbert's paper. For example, the 2018 book Belief, by psychology professor James Alcock, another supporter of the theory, misrepresents the theory in this way, citing Gilbert’s paper.

In addition to presenting apparent supporting observational evidence for Spinoza’s theory, albeit only in relation to comprehending claims, Gilbert presents a speculative explanation for this extreme credulity. He doesn't even briefly mention Spinoza's own argument, presumably because he was unable to follow it too.

He begins his argument with the premise that animals evolved to immediately believe what they perceive, and only question their perceptions afterwards, if at all. He argues that animals evolved to form beliefs via perception in this way because they often need to react quickly to their surroundings, and the content of their perceptions are a sufficiently reliable representation of their surroundings for this way of forming beliefs to be advantageous overall. He then says that perception is therefore 'quintessentially Spinozan'.

He next argues that cognition – thinking – could have evolved out of perception, given that both involve mental representations. That is, in the case of perception the mental representations are the content of perceptions, and in the case of cognition they’re the concepts, including the content of claims.

Also, both the perceptual process and the process of comprehending claims involve processing sensory data to create the mental representation, given that the latter process includes perception of the medium used to communicate a claim – which, again, is normally voice or text for humans.

He then argues that the Spinozan nature of perception could therefore have been inherited by the process of comprehending claims. That is, just as we immediately believe what we perceive, we immediately believe what claims we comprehend.

He points-out that most of us communicate true claims most of the time, quoting the late philosophy professor Daniel Dennett: ‘The faculty of communication would not gain ground in evolution unless it was by and large the faculty of transmitting true beliefs’. So, Gilbert argues, just as our perceptions are sufficiently reliable to allow us to immediately believe what we perceive, and thereby react quickly to our surroundings, so the claims we comprehend could be sufficiently reliable to allow us to immediately believe what claims we comprehend, and thereby react quickly to those claims.

But there are three fatal logical flaws in Gilbert's argument.

First, the idea that perception is 'quintessentially Spinozan' is the idea that the perceptual process directly produces beliefs about our surroundings or body, before we've undertaken any reasoning about the content of our perceptions. But, again, as I explained in the previous article, even the formation of beliefs about our surroundings or body via perception requires reason. Although, such reasoning is often so basic and therefore brief that the resulting belief can seem to be a direct product of the perceptual process.

Second, the idea that perception is 'quintessentially Spinozan' actually contradicts the idea that cognition could have evolved out of perception. That is, belief is the quintessential cognitive state, and so the idea that the capacity for belief pre-dated the evolution of cognition is nonsensical.

Third, the argument that I've presented in this article shows that our belief of claims upon comprehending them is simply a logically necessary aspect of claims entering the mind of any intelligent entity. By definition, an aspect of how the mind works that's logically inevitable can't have evolved. That is, even if there is a benefit to it, its evolution would have been unnecessary.

In sum, Gilbert's speculative explanation for Spinozan comprehension of claims is wrong, in addition to the argument failing to even attempt to explain Spinozan belief formation via the other three cognitive processes.

But the argument that I've presented in this article doesn't just support Spinoza's theory, and in full, it proves it, by showing that this extreme credulity is a logically necessary aspect of a claim entering the mind. Although, in addition to this theoretical proof, this extreme credulity must of course also be confirmed by observation – that is, experimentally.

Credulism and supposed intuitive belief

The idea of intuitive belief originated to explain beliefs that don't seem to form via reason. A supposed intuitive belief instead forms via some nebulous instinct. For example, we may form the belief that someone is lying to us, but not be aware of why we believe this, and so conclude that this belief is an intuition.

But such beliefs actually often do form via reason. Again, the brain functions on the timescale of milliseconds. And such beliefs can form via reasoning that's simply so short, and therefore brief, that we're unaware of it. In the above example, there may have been something in the person's body language, including their facial expression, that led us to conclude, reasonably or not, that they're lying, but this reasoning occurred within a fraction of a second and so we're unaware of it.

Also, as I said earlier, when we're aware that a belief formed upon us comprehending, imagining-up or recalling the claim concerned we can assume that the belief formed via reason or intuition just after the claim entered our mind. And we conclude that it was the latter when we're unaware of a plausible chain of reasoning that could have led to the belief.

In the example, the idea that the person is lying to us could instead enter our mind via our imagination. And if we're aware that our belief that they're lying formed upon this idea entering our mind via our imagination we can assume that this belief formed via reason or intuition just after this idea entered our mind. And we'll conclude that it was the latter if we're unaware of a plausible chain of reasoning that could have led to this belief.

So the idea of intuitive belief originated partly due to ignorance of credulism – and also helps maintain that ignorance.

Of course, when we're aware that a belief formed when the claim concerned entered our mind via reason, ignorance of credulism just means that we'll wrongly think that this belief formation was due to the claim being the product of that reason.

Why credulism matters

Knowing that our belief of a claim upon it entering our mind via reason isn’t due, as currently understood, to the claim being the product of that reason, and is instead due to merely that entrance, obviously matters in the sense that knowing the truth about the world, including our psychology, matters intellectually. But this truth doesn’t itself actually have significant implications for human psychology – and therefore also doesn't have significant implications for our lives.

However, the fact that merely comprehending, imagining-up or recalling a claim involves believing it, contrary to the prevailing understanding, and that this belief can last for any length of time, obviously does have significant implications for human psychology – and therefore also has significant implications for our lives.

Regarding such beliefs that we attribute to intuition, the fact that they actually don't arise via some nebulous instinct means that we should be a lot more questioning of them. But there's a much more significant implication of credulism.

In the next article I’ll present another highly counterintuitive theory about the psychology of belief – the theory that there aren't degrees of belief, that belief is certainty, and that this is so by logical necessity too, for any intelligent entity. And in subsequent articles I’ll show that credulism and the certainty of belief together explain cognitive biases.

Since the early 1970s, researchers have discovered a large number of these universal biases in human cognition. A Wikipedia page currently lists around two hundred of them, and the list keeps growing.

For example, confirmation bias is our cognitive bias towards interpreting, seeking and recalling information in a way that confirms, or helps to confirm, what we currently believe. And availability bias is our cognitive bias towards forming a belief on the basis of whichever relevant information happens to be most readily available to our mind, instead of suspending belief until we’ve checked for other relevant information.

Cognitive biases permeate all thinking. They underlie our consistent reasoning errors, including our consistent mathematical errors – which in turn includes our consistent statistical errors – and even those errors which occur when our reason is affected by our emotions. Cognitive biases therefore account for most of human irrationality.

There are many theories about why cognitive biases exist. Some only concern a single bias, whereas others try to unify several biases with a single explanation. All involve the cognitive bias or biases being ultimately due to the nature of the human brain.

But cognitive biases are actually simply manifestations of credulism and the certainty of belief, and so are simply logically necessary aspects of cognition, for any intelligent entity.

The idea that our cognitive bias to do X is logically necessary isn’t the idea that doing X is logically inevitable, but merely that our bias to do X is logically inevitable. Whether we ultimately do X is dependent on our nature and the nature of our situation. So a particular person not doing X in a particular situation doesn't disprove the idea that our bias to do X is logically necessary, because their not doing X could be despite being biased to do X.

Credulism and the certainty of belief therefore together provide a unifying explanation for all cognitive biases, and so for most of human irrationality.

Next article: The Impossibility of Degrees of Belief

How Belief Works