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

The answer to the question posed by the title of the previous article, Why do we believe what we believe?, is provided by a counterintuitive, and largely disregarded, theory of belief formation that was presented over three centuries ago – and which has profound implications for human psychology, and therefore also our lives.

A radical theory of belief formation

The theory was presented by the prominent 17th-century philosopher Baruch Spinoza, in his 1677 book Ethics.

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

• recollection – when we retrieve the claim from our memory

• reasoning – when we generate the claim using logic, whether our logic is good or bad and our premises are true or false

• imagination – when we generate the claim without using logic.

Spinoza’s theory is that the mere entrance of a claim into our mind, via any of these processes, causes us to believe it.

This theory can seem obviously false – which can itself seem to disprove it. It can seem obviously contrary to both the concept and experience of comprehending, recalling or imagining-up a claim. Regarding reasoning, the entrance of a claim into our mind via this process is a conclusion, which is by definition a belief. But Spinoza’s theory states 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 reasoning – which can seem obviously contrary to both the concept and experience of reasoning.

But closer analysis reveals that the theory actually isn’t contrary to our experience of a claim entering our mind via any of these processes. And although the theory is indeed contrary to the current concepts of comprehending, recalling and imagining-up a claim, and of reasoning, there’s no theoretical reason to think that these concepts can’t be revised to be compatible with the theory.

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

And the first conference on Spinozan belief formation took place in 2018, in the US.

This article presents a theoretical argument for Spinozan belief formation. To see why Spinoza was right, consider first the difference between thinking claim X and thinking about claim X.

Thinking X versus thinking about X

Thinking claim X is the mental state of believing X. For example, thinking 'David is vegetarian' is the mental state of believing that 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 reasoning. The mental state of concluding X involves thinking X, and to conclude X is by definition to believe X. 

Of course, we can 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.

It might be objected that thinking X isn’t necessarily the mental state of believing X. That is, it might be objected that if, for example, we believe that David isn’t vegetarian then we won’t reverse this belief simply by deliberately thinking 'David is vegetarian', like a silent mantra. However, I'm currently only concerned with organically thinking X – that is, when our thinking X is either a recollection of an apparent fact or the conclusion of reasoning, each of which are by definition the mental state of believing X. I’ll return later to deliberately thinking X.

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

Now consider thinking about claim X.

Whereas organically thinking X is the mental state of believing X, we obviously can think about X while not believing X. For example, we can think about the claim David is vegetarian while not believing that David is vegetarian.

We can actually think about a claim without it 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. However, I'm concerned here 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, unless I say otherwise.

The difference between thinking X and thinking about X means 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. For example, although thinking ‘David is vegetarian’ involves, by definition, the claim David is vegetarian existing in our mind, it doesn’t in itself involve thinking about this claim, given that thinking ‘David is vegetarian’ is different from thinking about this claim.

If we're thinking about claim X while apparently thinking X then we're actually not at that moment thinking X. Although, given the speediness of the brain, which functions on the timescale of milliseconds, 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.

So the mental state of believing claim X doesn't in itself actually involve thinking about claim X, because it involves thinking X. For example, the mental state of believing the claim David is vegetarian doesn't in itself actually involve thinking about the claim David is vegetarian, because it involves thinking 'David is vegetarian'.

It might be objected that thinking 'I believe the claim David is vegetarian' is the mental state of believing the claim David is vegetarian, which therefore involves thinking about this claim. But thinking 'I believe the claim David is vegetarian' is actually the mental state of believing that we believe the claim David is vegetarian.

Likewise, it might be objected that saying 'I believe the claim David is vegetarian' is our expression of our belief of the claim David is vegetarian, which therefore involves thinking about this claim. But saying 'I believe the claim David is vegetarian' is actually our expression of our belief that we believe the claim David is vegetarian. Our expression of our belief the claim David is vegetarian instead involves saying simply 'David is vegetarian'.

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 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 X is a true claim involves thinking about X.

Now consider how claim X's content exists in our mind as we’re thinking X or thinking about X.

The two ways that a claim's content 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 mind and the minds of others. So the content of our imagination 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. Also, concepts, being ideas, exist in our mind, and so are also part of reality in the sense of being part of mental reality.

A claim is analogous to a picture, in the sense that the content of both is a representation 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 many different ways to create a picture, such as painting, drawing, photography or using art software. Consider a painting.

A painting is ultimately just a collection of patches of paint on a surface. The picture we see as we look at this collection of patches of paint is our brain's interpretation of that 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 the collection of patches of paint as a picture, the painting and the picture seem to be the same thing.

The relationship between the 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 just a string of words – with, in the case of a written sentence, punctuation marks – 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 refer to 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, the picture we see as we look at a painting is the same as the picture we see as we look at a print of the 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 something 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 we see either a picture of the head of a rabbit – facing right – or a picture of the head of 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.

If the claim David is vegetarian isn't the sentence David is vegetarian, but what is asserted by this sentence, then 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 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. And so the mere concept that David is vegetarian is 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 abstinence from meat isn't a claim – indeed, these words don't form a declarative sentence. 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. So this claim and its content are 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 this claim's content is what is asserted by this sentence.

Analogously, in the case of the picture we see as we look at a painting, whereas the painting and its content, the picture, 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 picture's content. 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 pictured scene is in itself to say that the picture's content is an accurate representation of the pictured scene. And to say that the picture is what we see as we look at the painting is in itself to stay that the picture's content is what is what we see as we look at the painting.

In the case of the above duck-rabbit illusion, to stay that the picture changes depending on how our brain interprets the drawing is in itself to stay that the picture's content 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 a painting, 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 we see as we look at the painting.

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, despite the latter obviously being 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 believes that claim X is 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, it can be said that the content of the claim David is vegetarian is the concept of David being vegetarian.

Now consider the following thought experiment.

Imagine entering a room for the first time, and without prior knowledge that it has a fake window. A photorealistic painting of an outdoor scene has been framed with a window frame, without any space between the edge of the painting and the frame. The painting is translucent, and uniformly backlit with a light panel. And this assembly has been attached to the wall opposite the room entrance, so that when we enter the room we’re looking at it face-on.

The outdoor scene that we see within the window frame is what we'd see, from the room entrance, through a real window located where the fake window is. Also, that outdoor scene is one in which an absence of movement isn't unusual.

If upon us entering the room the fake window creates the illusion of a real window, at least in that moment, then our visual experience in that moment will consist of us apparently directly seeing a real outdoor scene through a real window. That is, it'll consist of us apparently directly seeing not a picture that looks just like a real outdoor scene, but simply a real outdoor scene.

And if the fake window doesn't create this illusion, even initially, then our visual experience in that moment will consist of us seeing merely a picture of an outdoor scene, as part of a fake window.

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

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

The picture's content existing in our vision as the content of this picture is analogous to a claim's content existing in our mind as the content of that claim. And it might be thought that this is the only conceivable way for a claim's content to exist in our mind as the claim exists in our mind. But without consideration of the above thought experiment it might similarly be thought that the only conceivable way for a picture's content to exist in our vision as the picture exists in our vision is as the content of that 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 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 claim X's content and the relevant aspect of reality, and then concluding that they match. That is, that assessment is based on claim X's content existing in our mind as both claim X's content and an aspect of reality. For example, our assessment that the claim David is vegetarian is a true claim is based on this claim's content – David being vegetarian – existing in our mind as both this claim's content and an aspect of reality.

So just as, in the fake window thought experiment, the picture's content can exist in our vision either as the content of a picture of an outdoor scene or as a real outdoor scene, a claims' content can exist in our mind either as that claim's content or as an aspect of reality. And the existence of claim X's content in our mind as an aspect of reality is the mental state of believing X.

Indeed, the mental state of believing X involves thinking X, and, as a matter of logic, thinking X can't in itself involve X's content existing in our mind as X's content.

As I explained in the previous section, the difference between thinking X and thinking about X means 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.

But X's content existing in our mind as X's content involves, by definition, thinking about X. For example, the content of the claim David is vegetarian existing in our mind as the content of this claim involves, by definition, thinking about this claim. Indeed, given that a claim and its content are the same thing, X's content existing in our mind as X's content is X's content existing in our mind as claim X – which, by definition, involves thinking about X.

So although thinking X involves, by definition, X's content existing in our mind, it can't in itself involve that content existing in our mind as X's content. For example, although thinking ‘David is vegetarian’ involves, by definition, this claim's content existing in our mind, it can’t in itself involve that content existing in our mind as this claim's content.

Given that a claim and its content are the same thing, it can be alternatively said that although thinking X involves, by definition, X existing in our mind, it can't in itself involve this claim existing in our mind as this claim, given that that would by definition involve thinking about X. For example, although thinking ‘David is vegetarian’ involves, by definition, this claim existing in our mind, it can’t in itself involve this claim existing in our mind as 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 picture's content can exist in our vision without existing in our vision as the picture's content, it can be said that the picture can exist in our vision without existing in our vision as that picture. But without consideration of this thought experiment it might be thought that the only conceivable way for a picture to exist in our vision is as that picture.

Also, again, claim X is concept X. So it can also be alternatively 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 this 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 this concept.

Again, given the brain's speediness, 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. Thus, thinking X can seem to in itself involve X's content existing in our mind as X's content. That is, thinking X can seem to in itself involve this claim existing in our mind as this claim – it can seem to in itself involve this concept existing in our mind as this concept.

It might be thought that if as we’re thinking ‘David is vegetarian’ this claim's content can’t exist in our mind as this claim's content, because that would involve thinking about this claim, then perhaps it exists in our mind as a claim's content but just not as a specific claim's content, which therefore wouldn't involve thinking about the claim David is vegetarian.

But, 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 a claim's content 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 a claim's content without existing in our mind as the content of the claim David is vegetarian.

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

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

Analogously, in the fake window thought experiment, if the picture's content doesn't exist in our vision as the content of this picture of an outdoor scene, then the only other logical possibility is that it exists in our vision simply as a real outdoor scene.

Regarding the conclusion that thinking claim X involves this concept existing in our mind not as this 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 this claim's content existing in our mind as a concept that's an aspect of reality.

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

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

Also, claim X's content 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 X's content existing in our mind as X's content.

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

Note that although the content of both a picture and a claim is a representation of reality, pictures and claims are themselves aspects of reality. Again, the picture we see as we look at a painting 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 also an aspect of mental reality. Indeed, a picture can appear in another picture, or be referred to by a claim. And a claim can be referred to by another claim, or the sentence expressing it can appear in a picture.

So, in the fake window thought experiment, although the picture's content 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 the 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 the painting in front of us.

Likewise, although I've been saying that claim X's content can exist in our mind as X's content or as an aspect of reality, the former is actually also X's content 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 X's content existing in our mind as an aspect of reality to solely mean that content existing in our mind not as 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, unless I say otherwise.

The analysis in this section provides the definition of belief that I gave in the first article, A Note on the Term Belief: a psychological state in which a claim's content exists in our mind, or at least our memory, as an aspect of reality. Or, given the previous point, more correctly: a psychological state in which a claim's content exists in our mind, or at least our 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

As I said, the analysis so far has only been concerned with organically thinking claim X – that is, when our thinking X is either a recollection of an apparent fact or the conclusion of reasoning, each of which are by definition the mental state of believing X. Now consider deliberately thinking X, like a silent mantra.

Again, it might be objected that thinking X isn’t necessarily the mental state of believing X. That is, it might be objected that if, for example, we believe that David isn’t vegetarian then we won’t reverse this belief simply by deliberately thinking 'David is vegetarian', like a silent mantra.

But the conclusion in the previous section that thinking X necessarily involves X's content existing in our mind not as X's content, but as an aspect of reality, and therefore necessarily involves believing X, equally applies to deliberately thinking X. Indeed, closer analysis reveals that this actually isn’t 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 the claim David is vegetarian immediately beforehand, and we may also think about this claim immediately afterwards, it doesn’t in itself involve thinking about this claim.

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 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.

As with organically thinking X, the difference between deliberately thinking X and thinking about X means that a claim can exist in our mind without us thinking about it. That is, although deliberately thinking X involves, by definition, X existing in our mind, it doesn’t in itself involve thinking about X.

But X's content existing in our mind as X's content involves, by definition, thinking about X. Indeed, given that a claim and its content are the same thing, X's content existing in our mind as X's content is X's content existing in our mind as claim X – which, by definition, involves thinking about X.

So, although deliberately thinking X involves, by definition, X's content existing in our mind, it can't in itself involve that content existing in our mind as X's content. For example, although deliberately thinking ‘David is vegetarian’ involves, by definition, this claim's content existing in our mind, it can’t in itself involve that content existing in our mind as this claim's content.

And the only two logically possible ways that a claim's content can exist in our mind are as the content of this claim about an aspect of reality or as that aspect of reality. So deliberately thinking X must involve X's content existing in our mind as an aspect of reality. And X's content existing in our mind as an aspect of reality is the mental state of believing X. So even deliberately thinking X, like a silent mantra, is the mental state of believing X.

And this inclusion of the claim's content into our understanding of reality continues beyond us deliberately thinking X, by being stored in our memory. 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, this isn't the end of our belief of X. That is, although we can think about X while not believing X, we can also think about X while believing X.

So why does it seem that we can deliberately think claim X without believing X? Consider again the scenario of believing that David isn’t vegetarian and then deliberately thinking 'David is vegetarian'.

Immediately after deliberately thinking, and thereby believing, 'David is vegetarian' 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 think this claim that we didn't believe, like a silent mantra. And so we’ll then organically think, and thereby believe, 'David isn't vegetarian'.

And given the simplicity of this subsequent thought process, 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 didn’t hold a belief about the subject of X immediately before doing so. Immediately after doing so we’ll be aware that we didn’t hold a belief about the subject of X immediately before doing so, and that we were thinking X just then only because we decided to think this claim, like a silent mantra. And so we’ll then organically think, and thereby believe, the claim that we're ignorant about the subject of X, with this belief therefore replacing our belief of X.

And given the simplicity of this subsequent thought process, 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 believed X. Immediately after doing so we’ll be aware that we were thinking X just then only because we decided to think this claim, like a silent mantra. But our belief of X immediately before doing so means that our belief of X won't cease just after doing so. And our belief of X upon and just after deliberately thinking X will seem to be due to our prior belief of X.

To summarise the critical points of the argument in this article so far:

If, as claim X exists in our mind, X's content exists in our mind as X's content then, by definition, we're thinking about X. And thinking about X is different from thinking X. So thinking X can’t in itself involve X's content existing in our mind as X's content. And the only other logically possible way that X's content can exist in our mind is as an aspect of reality. So thinking X must involve X's content existing in our mind as an aspect of reality. That is, however we come to be thinking X, doing so is always the mental state of believing X.

Now, finally, 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

• recollection – when we retrieve the claim from our memory

• reasoning – when we generate the claim using logic, whether our logic is good or bad and our premises are true or false

• imagination – when we generate the claim without using logic.

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 can involve thinking, or thinking about, a claim concerning X. For example, thinking about the claim David is vegetarian can involve thinking, or thinking about, a claim such as The claim 'David is vegetarian' is true, or Amy said that David is vegetarian.

However, I'm concerned here with X entering our mind by itself, upon being comprehended, recalled, concluded or imagined-up. So the question of whether that entrance consists of us thinking X or thinking about X only concerns thinking about X without thinking, or thinking about, a claim concerning X – which is what I mean when I subsequently refer to thinking about X, unless I say otherwise.

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, first, 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 – 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, and, possibly, the production of an output by that processing:

For example, the process of book manufacturing involves the processing of paper, ink and other materials – the inputs – to produce a book – the output. In the case of the cognitive process of thinking about X, X is obviously the main input to this process, with the other inputs being related information stored in our memory. And any output of this process is thought Y about X, whether Y is generated by our reasoning or imagination, or is recalled.

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

In the case of book manufacturing, the paper, ink and other materials used to produce a book are themselves the outputs of other processes. In the case of thinking about X, X is the output of the cognitive process of either comprehension, recollection, reasoning, or imagination:

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

So in order for the entrance of X into our mind to consist of us thinking about X – in order for the entrance of X into our mind to be the entrance of X into the process of thinking about X – the outputting of X from the first process must also be, in itself, the inputting of X into the process of thinking about X. That is, although something being inputted into a process is the opposite of something being outputted from a process, the outputting of X from the first process, and the inputting of X into the second process, must be different perspectives of the same event.

Consider the following analogy. When someone walks through a doorway connecting two adjacent rooms, their crossing of the threshold is them both exiting one room and entering another. So, although entering a room is the opposite of exiting a room, they can be different perspectives of the same event.

However, this supposed analogy is actually a false one.

Although walking is the product of countless processes inside our body, the person walking through the doorway isn't them being either outputted from a process or inputted into another process. That is, their crossing of the threshold isn't either the completion of the production of this person by a process or the beginning of the processing of this person by another process. So their exiting the first room being the same event as their entering the second room isn't an analogy of the outputting of X from the first process being the same event as the inputting of X into the process of thinking about X.

Indeed, the outputting of something from one process actually can't be the same event as the inputting of that thing into a second process.

Someone exiting any area of the physical world – in the sense of them moving through physical space out of that area – necessarily involves, in itself, them entering another area of the physical world, and vice versa. Even when someone walks from one room to another via a corridor, their exiting the first room is also them entering the corridor, and their entering the second room is also them exiting the corridor. Even when someone walks out of a building, their exiting the building is also them entering the area outside the building.

Someone exiting an area of the physical world, and them entering another area of the physical world, are different perspectives of the same event: them crossing the boundary between two adjacent areas of the physical world. So neither can occur without involving, in itself, the other.

But it's possible to conceive the outputting of something from one process not also involving, in itself, the inputting of that thing into a second process. That is, it's possible to conceive the completion of the production of something by a process not also involving, in itself, the beginning of the processing of that thing by a second process, with the latter instead occurring a period of time after that outputting, if at all.

And if it's possible to conceive outputting and inputting each occurring without involving, in themselves, the other then, by definition, they're different kinds of events. Indeed, the completion of the production of something is a different kind of event from the beginning of the processing of that thing.

And, by definition, different kinds of events can't ever be the same event. So outputting and inputting can't ever be different perspectives of the same event.

Of course, different kinds of events can occur simultaneously. But the only way that the outputting of something from one process, and the inputting of the same thing into a second process, could occur in the same moment is if they were the same event.

So when the output of one process is an input to a second, that inputting must occur after that outputting, although possibly immediately after. Even when the purpose of the first process is to feed something into the second process, the completion of the production of that thing by the first process to the second can't be the same event as the beginning of the processing of that thing by the second process, although they can be immediately consecutive.

Consider again the processes of paper and book manufacturing. Even if the outputting of paper from the first process and the inputting of that paper into the second process occur in the same location, they can't be the same event. That is, the completion of the production of the paper can't be the same event as the beginning of the processing of that paper by the process of book manufacturing.

Likewise, if there are intermediate processes – such as quality-checking the paper, or moving the paper to a different location for the process of book manufacturing – the outputting of paper from the process of paper manufacturing can't also be, in itself, the inputting of that paper into such processes.

Whatever the second process, the inputting of the paper into it must occur after its outputting from the first process, although possibly immediately after.

It might be thought that the process of paper decaying starts upon the paper forming, and so the outputting of paper from the process of paper manufacturing is, in itself, the inputting of that paper into the process of decay. But the above analysis implies that the process of decay must actually begin immediately after the paper forms.

So the outputting of claim X from the first process can’t also be, in itself, 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. It's possible that upon X being created, recreated or retrieved by the first process, X must then be transmitted to some central processing area of the brain in order to enter the mind. And that transmission of X to this area would itself be a process. But this process would 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 would be the production of X in this area.

So the entrance of X into our mind via any cognitive process can't itself consist of us thinking about X.

It might be thought that although:

• the outputting of claim X from the first process can’t also be, in itself, the inputting of X into the process of thinking about X

• comprehending, recalling, concluding or imagining-up X involves, by definition, the entrance of X into our mind

comprehending, recalling, concluding or imagining-up X may actually involve not just the first process – the process that creates, recreates or retrieves X – but also the process of thinking about X. That is, the first process and the process of thinking about X may actually be consecutive sub-processes of the process of comprehending, recalling, concluding or imagining-up X. And if the completion of this process involves the sub-process of thinking about X, then the entrance of X into our mind consists of us thinking about X.

However, consider the process of comprehending a claim, and consider that this cognitive task is indeed that – 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 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.

The performance of a task may involve the performance of sub-tasks, with such activities therefore being sub-processes. And the 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 single 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 indeed a single cognitive process, whether or not it involves sub-processes.

Also, 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 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.

But the first process and just the beginning of the process of thinking about X don't together constitute a single cognitive process. The beginning of a process involves inputting, whereas the completion of a process involves outputting. And, again, outputting and inputting are different kinds of events, and so can't be the same event. So the beginning of the process of thinking about X can't also be the completion of the process of comprehending X.

Therefore the process of comprehending X can't involve both the first process – the process that creates, recreates or retrieves X – and the process of thinking about X. And the same logic applies to the processes of recalling, concluding and imagining-up X.

So the entrance of claim X into our mind via any cognitive process indeed can't itself 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.

Again, 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 via any cognitive process must consist of us thinking X.

Indeed, the above analysis regarding thinking about X doesn't similarly apply to thinking X. That analysis showed that the entrance of X into our mind can't consist of us thinking about X because thinking about X is a cognitive process which follows, and so is separate from, the cognitive process by which X enters our mind. But thinking X is a specific thought, and a specific thought is the output of a cognitive process – which aligns with the entrance of X into mind being the output of the first process.

The conclusion that the entrance of X into our mind via any cognitive process must consist of us thinking X, together with the conclusion of the previous section 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 must be 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 that led to that entrance.

That is, the conclusion that the entrance of X into our mind via any cognitive process can't itself consist of us thinking about X, and so must always consist of us thinking X, doesn’t depend on the nature of the cognitive processes that can lead to that entrance. And the analysis which shows that thinking X is always the mental state of believing X, however we come to be thinking X, doesn't even refer to the cognitive processes that can lead to us thinking X, and only considers how X's content exists in our mind as we're thinking X.

So the mere entrance of a claim into our mind, whether via comprehension, recollection, reasoning or imagination, causes us to believe it.

And this inclusion of the claim's content into our understanding of reality continues beyond the claim's entrance into our mind, by being stored in our memory. 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, 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.

So Spinoza was right. This theory of belief formation could be called credulism, given its extreme claim about our credulity. Again, credulism has profound implications for human psychology, and therefore also our lives, as I'll explain.

But, again, credulism can seem obviously false – which can itself seem to disprove it. It can seem obviously contrary to both the concept and experience of comprehending, recalling or imagining-up a claim. Regarding reasoning, the entrance of a claim into our mind via this process is a conclusion, which is by definition a belief. But credulism states 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 reasoning – which can seem obviously contrary to both the concept and experience of reasoning.

But consider, first, comprehending a claim.

Credulism and comprehending a claim

Consider our experience of comprehending a claim.

It can seem obvious from this experience that the entrance of a claim into our mind upon comprehending it doesn't cause us to believe it. For example, it can seem obvious from our experience of comprehending the claim London is the capital of France that the entrance of this claim into our mind upon comprehending it doesn't cause us to wrongly believe that London is the capital of France. Indeed, it can seem obvious that we instead immediately think/believe 'London isn't the capital of France'.

However, given that our thinking that London isn't the capital of France is a response to the comprehended claim, it must occur immediately after we've comprehended that claim. So this 'immediate' thought/belief actually doesn't mean that we don't believe the comprehended claim upon comprehending it, which we do – but that belief only lasts a fraction of a second.

The comprehended claim 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 requires very little thinking – as does 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 lasts a fraction of a second. 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 false 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, upon hearing someone say that it'll rain tomorrow this claim will likely seem obviously uncertain, given that no weather forecast can be infallible. But even if it does 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 tomorrow. 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 seem obviously 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 have any reason to disbelieve or even doubt this, especially if we don't know anything about David. 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. And thinking about X is different from thinking X. So although thinking/believing X constitutes this belief being involved in our thinking, it doesn't in itself actually involve thinking about this belief. That is, thinking/believing X doesn't in itself actually involve being aware of our belief of X.

For example, although thinking/believing ‘David is vegetarian’ constitutes this belief being involved in our thinking, it doesn’t in itself actually involve thinking about this belief. That is, it involves, in itself, thinking about David being vegetarian without thinking about our belief that David is vegetarian. The former thinking involves thinking solely about one of David's dietary choices, and so only the latter thinking involves thinking about our belief about one of David's dietary choices.

So just as a claim can exist in our mind without us thinking about it, a belief can be involved in our thinking without us thinking about it, because we can think about the content of the belief without thinking about our belief of that content.

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 speediness of the brain, 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.

Now consider comprehending a claim that doesn't seem obviously false or uncertain, but which we didn't already believe.

Although our absence of uncertainty in the claim means that our resulting belief can last long enough for us to be able to be aware of both it and our credulity, it also means that we tend not to be motivated to question, and thus think about, this belief. That is, our absence of uncertainty means that we tend to think about the content of the belief without thinking about 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 goals, often including how best to interact with other people.

This cognitive activity involves a constant stream of belief formation. And, again, it's just 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 seem obviously 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 thus think about, our belief of it. And for many of our beliefs the 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.

Finally, we can, as I've mentioned previously, continue to hold a belief when it's no longer involved in our thinking. But thinking about a belief obviously involves it being involved in our thinking.

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 still 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, generally, the more time that has passed since a 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 this 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 such a belief, past or present, we may not remember that it formed around when we heard or read the claim concerned. And even if we do we can assume that the belief formed just after our comprehension of the claim, via our reasoning or intuition.

In sum, 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 seems obviously false or uncertain – and so we have no awareness of the belief, or it 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.

So although we're occasionally aware of our credulity upon comprehending a claim, credulism can seem obviously contrary to our overall experience of comprehending claims, even though closer analysis reveals that it isn't.

Consider also our experience of other people comprehending claims.

We're by nature motivated to try to understand the world around us, which includes understanding 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 seems to them obviously 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 around when they comprehended 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 their reasoning or intuition.

And in the case of someone comprehending a claim that we think they already believed, we can 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 comprehending claims than we are of our own, credulism can still seem obviously contrary to our overall experience of other people comprehending claims, even though closer analysis reveals that it isn't.

It might be objected that it's both obvious from experience and 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 can affect whether we believe the claim, contrary to credulism.

But, again, if we're aware that one of our beliefs, past or present, formed around when we comprehended the claim concerned, we can assume that it formed just after our comprehension of the claim, via our reasoning 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. 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 can affect whether we believe the claim, but only after we comprehend/believe it. That is, it can only affect 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.

Now consider the concept of comprehending a claim.

Credulism is indeed contrary to the current concept of comprehending a claim, according to which the entrance of the claim into our mind upon comprehending it doesn't cause us to believe it. That is, the current concept involves the claim's content entering our mind as merely a claim's content rather than as an aspect of reality.

But the current concept arose partly from the fact that, as I explained, we tend not to be aware of our credulity upon comprehending a claim. Also, any conception of comprehending a claim must, by definition, involve the claim entering our mind, and it has been wrongly assumed that this is all that comprehending a claim involves.

There’s no theoretical reason to think that the concept of comprehending a claim can’t include the entrance of the claim into our mind causing us to believe it, however counterintuitive this idea can seem. Indeed, as I've shown, there's theoretical reason to think that this concept must include this. That is, the concept must involve the claim's content entering our mind not as merely a claim's content, but as an aspect of reality. Although, the claim's content may exist in our mind as a claim's content within a fraction of a second of us comprehending the claim, upon us thinking about the claim.

Note that although the revised concept of comprehending a claim includes the claim being believed, it's still about simply the claim entering our mind. That is, to refer to someone comprehending claim X is still to refer simply to X entering their mind via the process of comprehension. The change is that it's understood that their comprehending X involves believing X, because the entrance of a claim into our mind causes us to believe it.

Now consider recalling or imagining-up a claim.

Credulism and recalling or imagining-up a claim

Consider first our experience of recalling or imagining-up a claim.

It can seem obvious from this experience that the entrance of a claim into our mind upon being recalled or imagined-up doesn't cause us to believe it. But the analysis in the previous section similarly applies.

That is, when we recall or imagine-up a claim that we didn't already believe, our resulting belief of it either only lasts a fraction of a second – if the claim seems obviously false or uncertain – and so we have no awareness of it, or it 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 recalling or imagining-up 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.

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

Regarding imaging-up a claim, this can be deliberate or spontaneous. That is, a claim can enter 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 could enter our mind via our imagination because we decided to use our imagination to generate a claim about David, or 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, immediately after doing so we’ll be aware that the claim is simply the product of our imagination, and so it’ll at least seem obviously uncertain for that reason. That is, even if the claim doesn’t otherwise seem obviously uncertain, or seem obviously false, our belief of it will only last a fraction of a second, and so we’ll have no awareness of it.

Recalling a claim can also be deliberate or spontaneous. That is, we can recall a claim because either we made an effort to do so or something triggered the recollection. But, in the case of the former, if immediately after the claim enters our mind we think about the fact that it did so due to our deliberate effort to recall it, then that won't in itself give us reason to be uncertain about it.

This is most obvious in the case of deliberately recalling an apparent fact – that is, a claim that we believed immediately before recalling it. If immediately after the claim enters our mind we think about how it did so, then that obviously won't in itself give us reason to be uncertain about it.

Comprehending a claim is inherently deliberate. And if immediately after the claim enters our mind we think about the fact that it did so due to our deliberate effort to comprehend it, then that also won't in itself give us reason to be uncertain about it. As with deliberately recalling a claim, this is most obvious in the case of comprehending a claim that we already believe. If immediately after the claim enters our mind we think about how it did so, then that obviously won't in itself give us reason to be uncertain about it.

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

I also addressed in the previous section the potential objection that it seems both obvious from experience and true by definition that if we comprehend a claim that we didn't already believe, our level of trust in the claim's source on the subject of the claim can affect 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.

Now consider the concepts of recalling and imagining-up a claim. Again, the analysis in the previous section similarly applies.

Credulism is indeed contrary to the current concepts of recalling and imagining-up a claim, according to which the entrance of the claim into our mind upon being recalled or imagined-up doesn't cause us to believe it. That is, the current concepts involve the claim's content entering our mind as merely a claim's content rather than as an aspect of reality.

But the current concepts arose partly from the fact that, as I explained, we tend not to be aware of our credulity upon recalling or imagining-up a claim. Also, any conception of recalling or imaging-up a claim must, by definition, involve the claim entering our mind, and it has been wrongly assumed that this is all that recalling or imaging-up a claim involves.

There’s no theoretical reason to think that the concepts of recalling and imaging-up a claim can’t include the entrance of the claim into our mind causing us to believe it, however counterintuitive this idea can seem. Indeed, as I've shown, there's theoretical reason to think that these concepts must include this.

That is, these concepts must involve the claim's content entering our mind not as merely a claim's content, but as an aspect of reality. Although, the claim's content may exist in our mind as a claim's content within a fraction of a second of us recalling or imagining-up the claim, upon us thinking about the claim.

Note that although the revised concepts of recalling and imagining-up a claim include the claim being believed, they're still about simply the claim entering our mind. That is, to refer to someone recalling or imagining-up claim X is still to refer simply to X entering their mind via their memory or imagination. The change is that it's understood that their recalling or imagining-up X involves believing X, because the entrance of a claim into our mind causes us to believe it.

I've said that organically thinking X is when our thinking X is either a recollection of an apparent fact or the conclusion of reasoning. But, actually, even comprehending X, recalling X when we didn’t believe X immediately before doing so, and imagining-up X, involve organically thinking X, given that they don't involve deliberately thinking X, like a silent mantra. Indeed, by definition, none of them involve thinking about X before thinking X. Also, deliberately thinking X is always preceded by organically thinking X, given that it's dependent on recalling this claim that we decided to think.

Now consider reasoning.

Credulism and reasoning

Again, the entrance of a claim into our mind via reasoning is a conclusion, which 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 reasoning – which can seem obviously contrary to both the concept and experience of reasoning.

But consider first the concept of reasoning.

Reasoning involves determining apparent logical implications of particular premises. For example, if we have to make a meal for David, and need to decide what to make, and we learn that he's vegetarian, then our reasoning 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.

What follows logically from particular claims is of course independent of the truth of those claims and of the logical implications of them. For example, the claim David doesn't eat meat is a logical implication of the claims David is vegetarian and Vegetarians don't eat meat whether or not these three claims are true.

So the process of determining a logical implication of particular claims isn't itself concerned with the truth of those claims or of the apparent logical implication of them. Therefore, although this process explains our belief that claim X is a logical implication of the claims that are our premises, it doesn’t by itself explain our belief of X upon it entering our mind as that logical implication.

According to the current concept of reasoning, our belief of X upon it entering our mind as a logical implication of our premises is due to the combination of that process of logical inference and our belief of those premises. But credulism implies that our belief of X upon it entering our mind as a logical implication of our premises is actually due merely to that entrance.

Of course, when we form a conclusion our belief of our premises was 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 reasoning. It's due merely to the entrance of the claim into our mind upon being produced by our reasoning. So our reasoning leads to, but doesn't itself cause, our belief of the claim upon it entering our mind. In other words, although to conclude claim X is by definition to believe X, we don't believe X because we've concluded X – instead, we conclude/believe X because X entered our mind via our reasoning.

So although credulism is indeed contrary to the current concept of reasoning, it's that concept that's wrong. There’s no theoretical reason to think that this concept can't involve the belief formation being due to the mere entrance of the claim into our mind, however counterintuitive this idea can seem. Indeed, as I've shown, there's theoretical reason to think that this concept must involve this.

Now consider our experience of reasoning.

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

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 reasoning or to the mere entrance of the claim into our mind upon being produced by that reasoning. That is, either way this experience would consist of us forming a belief of the claim upon it entering our mind via our reasoning.

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 is due to the claim being the product of our reasoning is actually merely our interpretation of this experience, based on the current concept of reasoning.

And the same applies to our experience of other people forming beliefs via reasoning: this experience would be the same whether this belief formation is due to the claim being the product of the person’s reasoning or to the mere entrance of the claim into their mind upon being produced by that reasoning. 

It might be thought that there are some occasions when credulism is definitely contrary to our experience of reasoning.

We sometimes generate a claim via logic that we believe is flawed or questionable. For example, we knowingly apply flawed or questionable logic to particular premises in order to illustrate such logic. We also 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 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. But X does first enter our mind by itself, upon being generated by the unsound logic. 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. And 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.

Another potential objection

It might be objected 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 concerns 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 process of generating a claim about X with our reasoning 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.

But 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, our resulting belief that the claim David is vegetarian is false is immediately preceded by us believing that David is vegetarian, and immediately followed by us concluding that David isn't vegetarian. Although, our subsequent thinking may lead to us again believing that David is vegetarian within a further fraction of a second.

Even 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, isn't also comprehending Y, because comprehending Y is dependent on us then combining our comprehension of X with our comprehension of that 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.

In sum, however claim Y enters our mind, our thinking/believing Y in that moment, which indeed involves thinking about claim X, must be preceded by us thinking/believing X.

The logical necessity of credulism

The argument I presented for credulism actually has a doubly counterintuitive conclusion. That argument is purely conceptual – that is, it doesn’t at any point depend on observational evidence. So it 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 to logical necessity.

The central tenet of the field of psychology today is that how the human mind works is 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.

Another tenet of the field of psychology today is that using logic alone to reach conclusions about human psychology is unscientific, given the absence of observational evidence in such reasoning. But at the beginning of modern science the use of mathematics, a form of logic, alone to reach conclusions about nature, rather than in conjunction with observational data, was controversial. And yet in science today this is accepted as a legitimate way to further our understanding of nature. For example, much of theoretical physics is the use of mathematics, and non-mathematical logic, alone to develop and refine theories.

The logical necessity of credulism shows that using logic alone is a legitimate way to further our understanding of human psychology. 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 we believe claim X because we’ve assessed that X is true is fatally logically flawed, and the reality is actually the other way around. And at the end of that article I raised an alternative possible answer to the question of why we believe what we believe: we believe X because we’ve concluded X. That is, we believe X because this claim was the product of our reasoning – however brief, faulty, emotional or credulous our reasoning was. As I explained, even the formation of beliefs about our surroundings or body via sensory perception requires at least some reasoning.

But the analysis in this article shows that even this seemingly irrefutable theory is fatally logically flawed.

That is, by logical necessity, our belief of X upon X entering our mind via our reasoning is due merely to that entrance rather than to X being the product of that reasoning. So, by logical necessity, although to conclude X is by definition to believe X, we don't believe X because we've concluded X – instead, we conclude/believe X because X entered our mind via our reasoning. And, also by logical necessity, the entrance of X into our mind via any other cognitive process – whether comprehension, recollection or imagination – also causes us to believe it.

Vindicating Spinoza

The argument I presented for credulism actually isn’t Spinoza’s, but was developed by me. Spinoza used an obscure philosophical argument which at one point refers to the geometry of a triangle, and at another point refers to an imaginary winged horse. I'm not enough of a philosopher to be able to follow and assess his argument, but this philosophy paper states that several modern philosophers have independently concluded that it's flawed.

The obscurity and apparent unsoundness of Spinoza’s argument partly explains why belief in his counterintuitive theory has, ironically, been very low since it was published in 1677.

The most prominent modern piece of scholarship on the theory is a 1991 paper called ‘How Mental Systems Believe’, by Harvard psychology professor Daniel Gilbert, one of the relatively few academics who support the theory. It catalogues apparent supporting evidence, including experimental research – which I’ll review, along with other apparent supporting evidence, in an upcoming article in this series.

But the 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 papers and books 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 paper or book 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 evidence for Spinoza’s theory in relation to comprehending claims, Gilbert presents a speculative evolutionary explanation for this extreme credulity.

He begins 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 accurate representation of their surroundings. He then says that perception is therefore 'quintessentially Spinozan'.

He next suggests that cognition could have evolved from perception, given that both involve mental representations. That is, in the case of perception the mental representations are the content of our perceptions, and in the case of cognition they’re the content of claims involved in our cognition. 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 our perception of the medium used to communicate a claim – which, again, is normally voice or text.

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 also points-out that most people communicate true claims most of the time, quoting 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 suggests, just as the general reliability of our perceptions allows us to immediately believe what we perceive, and thereby react quickly to our surroundings, so the general reliability of the claims that people communicate allows us to immediately believe what claims we comprehend, and thereby react quickly to those claims.

But there are three significant problems with 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, the formation of beliefs about our surroundings or body via sensory perception requires at least some reasoning. 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.

A second problem is that the idea that perception is 'quintessentially Spinozan' actually contradicts the idea that cognition evolved from perception and thereby inherited its Spinozan nature. That is, belief is the quintessential cognitive state, and so the capacity for belief can't pre-date the evolution of cognition.

A third problem is that even if the evolution of communication indeed implies that most communicated claims are true, the communication of false claims, deliberately or not, is obviously a common occurrence. Our belief of such claims will naturally tend to have negative consequences for us, from minor to major, and it's implausible that the proportion of communicated claims that are true is sufficiently high to allow the evolution of our immediate belief of every claim that we comprehend.

Indeed, given the biological value of taking advantage of credulity by lying, the greater the credulity in our species, the greater the evolutionary pressure towards lying, and so, eventually, the greater the frequency of lying, and so the greater the evolutionary pressure away from credulity, given the biological cost of believing false claims.

This point is used by the cognitive scientist Hugo Mercier in his 2020 book Not Born Yesterday, on our degree of gullibility, to argue against the idea that we always immediately believe claims upon comprehending them. But Mercier’s reasoning doesn't take into account the possibility that such extreme credulity is simply logically inevitable, and that its biological cost is therefore irrelevant to whether it occurs. That is, his reasoning is based on the central tenet of the field of psychology today that how the human mind works is due solely to the nature of the human brain, which is the product of evolution.

Mercier uses in his book ‘the latest findings from experimental psychology to show how each of us is endowed with sophisticated cognitive mechanisms of open vigilance'. He defines 'open vigilance' as being open to the possibility that comprehended claims are true while also being vigilant against falsehoods.

But, ironically, if such cognitive mechanisms exist they'll actually be at least partly due to, rather than evidence against, our extreme credulity. That is, given that this extreme credulity is logically inevitable, but biologically costly, it creates an evolutionary pressure towards the development of cognitive mechanisms that can somewhat counteract it.

In sum, Gilbert's argument fails to support Spinozan's theory in relation to claims entering our mind via comprehension, in addition to not even addressing the theory in relation to claims entering our mind via the other three possible cognitive processes.

The argument I presented doesn't just support Spinozan'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 experimentally.

Credulism and supposed intuitive belief

The idea of intuitive belief originated to explain beliefs that don't seem to form via reasoning. That is, a supposed intuitive belief apparently instead forms via some nebulous instinct. For example, if we're having an in-person conversation with someone and they make a claim, we may form the belief that they're lying, 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 reasoning. 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 other person's body language, including their facial expression, that led us to conclude, whether 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 when the claim concerned entered our mind via our comprehension, recollection or imagination we can assume that the belief formed via our reasoning just after the claim entered our mind. But if we try and fail to think of a chain of reasoning that could have led to the belief we often then attribute the belief to intuition.

In the example, the idea that the other person is lying could instead enter our mind via our imagination. And if our resulting belief of it lasts long enough for us to become aware of it, and we try and fail to think of a chain of reasoning that could have led to it, we may attribute it to intuition.

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 our reasoning, ignorance of credulism just means that we'll wrongly think that this belief formation was due to the claim being the product of that reasoning.

Why credulism matters

The fact that our belief of a claim upon it entering our mind via our reasoning isn’t due, as currently understood, to the claim being the product of that reasoning, and is instead due to merely that entrance, doesn’t itself actually have significant implications for human psychology and therefore our lives. Although, knowledge of how beliefs form via reasoning at least matters in the sense that knowing the truth about the world, including our psychology, matters intellectually.

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

Regarding such beliefs that we attribute to intuition, the fact that they therefore 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 a second 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. 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 making a judgement on the basis of whichever relevant information happens to be most readily available to our mind, instead of suspending judgement until we’ve checked for other relevant information.

Cognitive biases underlie our consistent reasoning errors. These include our consistent mathematical errors, which in turn includes our consistent statistical errors. And they even include those errors which occur when our reasoning 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 due to the nature of the human brain.

But I'll show that all cognitive biases are simply manifestations of credulism and the certainty of belief, and so are simply logically necessary aspects of cognition, for any intelligent entity.

Note that the idea that our cognitive bias to do X is logically necessary isn’t the idea that us 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 we've a logically inevitable bias to do X.

I'll therefore show that credulism and the certainty of belief together provide a unifying explanation for all cognitive biases, and thus for most of human irrationality.

Next article: The Logical Impossibility of Degrees of Belief

How Belief Works