How Belief Works

Chapter 5: How Beliefs Form​

A radical new/old theory​

In chapter 3 I raised the question of why we believe what we believe. And I showed that, as a matter of surprisingly basic logic, the current understanding that we believe claim X because we’ve assessed that X is true is wrong, because the reality is actually the other way around. But at the end of that chapter I raised another possibility: we believe X not because we've concluded that X is true, but simply because we've concluded X. That is, we believe X because X was the product of our reasoning. As I explained, even the formation of beliefs about our surroundings via perception involves at least some reasoning about the content of our perceptions.

However, as I pointed-out, although this theory of belief formation can seem true by definition and therefore unimpeachable, so did the theory that we believe something because we’ve assessed that it’s true. Indeed, even this second theory is wrong. We actually believe X simply because X has entered our mind. That is, by logical necessity, the mere entrance of a claim into our mind, whether via reasoning, comprehension, imagination or recollection, causes us to believe it, and this is the cause of all belief formation. Regarding reasoning, our belief of the claim upon it entering our mind is therefore due not to the claim being the product of our reasoning, but merely to that entrance. Although this can initially seem obviously contrary to experience, closer analysis reveals that it isn't.

As I mentioned in chapter 1, this theory was first proposed by the prominent 17th-century philosopher Baruch Spinoza, although he used an obscure theoretical supporting argument that seems to be unsound. However, I developed an alternative theoretical argument that vindicates Spinoza. And the truth of his theory has profound implications for human psychology and therefore our lives especially, as I explained in chapter 4, in combination with the theory of the certainty of belief.

Why a claim and its content aren't the same thing

First consider that, contrary to what can be assumed, a claim and its content aren't the same thing.

As I stated in chapter 2, although a claim can be about anything, all claims are ultimately about one thing: reality. Again, reality consists of:

    • physical reality – the physical world

    • mental reality – our mind and other minds

    • mathematical reality – for example, 2 + 2 = 4

    • logical reality – for example, a logical implication of the claims Vegetarians don’t eat meat and Pork sausages contain meat is Vegetarians don't eat pork sausages.

And claims can be about the physical and mental reality of the past, present and future.

The interactions and relationships between people, and the creation and effects of rules, conventions, and norms, involves a combination of the above aspects of reality, and includes ethics and politics. Also, note that the content of someone's imagination is part of reality in the sense that it's part of mental reality. Also, although it might be thought that false claims aren't claims about reality, given that their content don't match reality, even a false claim is indeed a claim about reality – it's just that this claim about reality is false.

An analogy of a claim is a painting of a scene, given that both convey information about reality, however accurately. That is, just as a claim is a linguistic representation of part of reality, a painting of a scene is a pictorial representation of part of reality. Indeed, we sometimes say that a particular description 'paints a picture'. Even if the scene in a painting originated in the artist's imagination, the painting is then a pictorial representation of the reality of the content of their imagination.

And this analogy shows that a claim and its content aren't the same thing. A painting of a scene consists of patches of paint on a surface, whereas its content is the scene that we see in the painting, and which to some degree matches a scene in either the physical world or the painter's imagination. Likewise, a claim, being an assertion, consists of a sentence, whereas its content is what is being asserted by that sentence. For example, the claim that David is vegetarian consists of the sentence David is vegetarian, whereas its content is David being vegetarian. But a claim and its content can seem to be the same thing due to their close relationship.

Thinking X versus thinking about X

Now compare thinking claim X and thinking about X.

Thinking 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 term think to refer to our, or someone else's, belief of something. For example, we may refer to Amy’s belief that David is vegetarian by saying ‘Amy thinks that David is vegetarian’.

It might be objected that although the mental state of believing X necessarily involves thinking X, the reverse isn't true in the case of deliberately thinking a claim, like a mantra. For example, it can seem obvious that if we believe that David isn’t vegetarian, then we won’t reverse that belief simply by deliberately thinking the claim David is vegetarian, like a mantra. However, I'm currently only referring to thinking X in the sense of doing so organically, as part of our chain of thinking. I'll return later to thinking X in the sense of doing so because we decided to think this claim, like a mantra.

Now consider thinking about X. This involves involves either contemplating X or thinking a specific claim about X. For example, we can contemplate the claim David is vegetarian or think a specific claim about it, such as Amy said that David is vegetarian. And whereas thinking X is the mental state of believing X, we can think about X without believing X.

We can actually think about X without this sentence existing in our mind. That is, if we know about the existence of X, but don't currently know what it is, then we can at least think about X in the sense of thinking about its existence. For example, we may know that Amy said something to David about her dietary requirements, but not yet know what she said. However, I'm concerned here, and in the subsequent sections, with thinking about X in the sense that involves this sentence existing in our mind, as thinking X does.

The difference between thinking X and thinking about X can be considered in terms of the distinction between a claim and its content. Thinking about X involves thinking about both this claim and its content. For example, thinking about the claim David is vegetarian involves thinking about both the sentence David is vegetarian and David being vegetarian. To be clear, we can think about David being vegetarian without believing that David is vegetarian. But thinking X involves thinking only about the content of this claim. For example, thinking David is vegetarian involves thinking about David being vegetarian, but doesn't itself involve thinking about the sentence David is vegetarian.

So, although thinking X involves X existing in our mind, it doesn't itself involve thinking about X. If we're thinking about X while apparently thinking X, then we're actually not, at that moment, thinking X. Although, we can think about X immediately before or after thinking X, and it may then seem that our thinking X involved that thinking about X.

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

Now consider how the content of claim X exists in our mind when we're thinking/believing X or thinking about X.

The mental state of thinking/believing X doesn't itself involve the content of X existing in our mind as a claim's content that matches reality, because that's the content of X existing in our mind as the content of a claim that's true, which is the mental state of believing X is true, not X. Also, thinking/believing X doesn't even itself involve the content of X existing in our mind as the content of a claim that we believe, because that's actually the mental state of believing that we believe X.

Indeed, the existence of the content of X in our mind as the content of a claim that's true, or that we believe, constitutes thinking about X, and therefore doesn't itself constitute thinking X. And this point has the counterintuitive implication that the mental state of thinking/believing X can't itself involve the content of X existing in our mind as the content of a claim at all. It can seem obvious that if a claim exists in our mind then its content exists in our mind as the content of that claim. How else could it exist in our mind? However, given that the existence of the content of X in our mind as the content of a claim constitutes thinking about X, and thinking/believing X doesn't itself involve thinking about X, thinking/believing X can't itself involve the content of X existing in our mind as the content of a claim. To understand how it does exist in our mind, consider again the analogy of a painting of a scene.

Imagine that a photorealistic painting of an outdoor scene is used to try to create the illusion of a window in a room. The canvas is translucent and backlit, and the painting is framed using a window frame, without any space between the edge of the painting and the frame. This fake window is then attached to the wall opposite the entrance to the room, so that upon entering the room we're looking at the fake window face-on. The content of the painting is what we'd see, from the room entrance, through a real window located where the fake window is. And that outdoor scene is one in which an absence of any movement won't seem odd, at least initially.

This photograph is actually of a real window that looks somewhat like a backlit painting, but it illustrates how one can be confused for the other.

If upon entering the room and looking at the fake window the illusion is successful, at least in that moment, then our visual experience at that moment will consist of seeing a real outdoor scene through a real window. And if the illusion isn’t successful then our visual experience at that moment will consist of seeing merely a picture of an outdoor scene in a fake window.

So, as we look at the fake window, the content of the painting exists in our vision either as the content of a picture of an outdoor scene or as a real outdoor scene. And if, as we’re seeing the outdoor scene in the painting, our visual experience doesn’t consist of seeing a picture of an outdoor scene, then the only other logical possibility is that it consists of directly seeing a real outdoor scene. Conversely, if, as we’re seeing the outdoor scene in the painting, our visual experience doesn’t consist of directly seeing a real outdoor scene, then the only other logical possibility is that it consists of seeing a picture of an outdoor scene.

Likewise, if the content of a claim exists in our mind, but not as the content of a claim, then the only other logical possibility is that it exists in our mind as part of reality – that is, not as a claim's content that matches reality, but simply as part of reality. Therefore, the mental state of thinking/believing X involves the content of X existing in our mind as part of reality:

For example, when we're thinking about the claim David is vegetarian, the content of this claim – David being vegetarian – exists in our mind as the content of this claim. But when we're thinking/believing David is vegetarian, the content of this claim exists in our mind not as the content of this claim, but as part of reality.

Although, given that we can think about X immediately before or after thinking/believing X, the content of this claim can exist in our mind as the content of a claim immediately before or after thinking/believing X – and it may then seem that our thinking/believing X involved the content of this claim existing in our mind as the content of a claim.

The conclusion that thinking/believing X involves the content of X existing our mind as part of reality is compatible with my definition of belief, in chapter 2, as an understanding of part of reality.

The existence of the content of X in our mind, during the mental state of thinking/believing X, as part of reality rather than as the content of a claim is a second difference between the beliefs X and X is true. That is, not only do these beliefs involve different claims, but the latter belief involves the content of X existing in our mind as the content of a claim – a claim that's true. When thinking/believing X is true, it's the content of the claim X is true that exists in our mind as part of reality rather than as the content of a claim.

As I stated in chapter 3, whereas believing X doesn't itself involve believing that X is true, disbelieving X involves believing that X is false. Therefore, the mental state of disbelieving X involves the content of X existing in our mind as the content of a claim – a claim that's false. Indeed, that content obviously doesn't exist in our mind as part of reality, given our disbelief.

Also, the two ways that the content of a claim can exist in our mind reveals another flaw in the idea of degrees of belief, in addition to the three that I listed in chapter 4. According to this idea, our confidence in X constitutes our belief of X if that confidence is above a particular sub-certain level. But our confidence in X is a feeling about whether this claim is true, and therefore involves the content of X existing in our mind as the content of a claim.

Thinking X is always believing X

As I mentioned, the analysis so far has only been referring to thinking X in the sense of doing so organically, as part of our chain of thinking, and therefore hasn't been referring to thinking X in the sense of doing so because we decided to think this claim, like a mantra. And whereas organically thinking X is the mental state of believing Xthat is, organically thinking David is vegetarian is the mental state of believing that David is vegetarianit can seem obvious that deliberately thinking X, like a mantra, doesn't inherently involve believing X. However, the logic of the analysis so far actually equally applies to the latter kind of thinking X.

Consider again the difference between thinking X and thinking about X in terms of the distinction between a claim and its content. Thinking about X involves thinking about both this claim and its content. For example, thinking about the claim David is vegetarian involves thinking about both the sentence David is vegetarian and David being vegetarian. Again, to be clear, we can think about David being vegetarian without believing that David is vegetarian. But although deliberately thinking X, like a mantra, involves thinking about this claim immediately beforehand, and we may also think about this claim immediately afterwards, it itself only involves thinking about the content of this claim. For example, deliberately thinking David is vegetarian, like a mantra, involves thinking about David being vegetarian, but doesn't itself involve thinking about the sentence David is vegetarian.

So, although deliberately thinking X, like a mantra, involves X existing in our mind, it doesn't itself involve thinking about X. If we're thinking about X while apparently deliberately thinking X, like a mantra, then we're actually not, at that moment, thinking X. Although, we can think about X immediately before or after thinking X, and it may then seem that our thinking X involved that thinking about X.

Therefore, deliberately thinking X, like a mantra, can't itself involve the content of X existing in our mind as the content of a claim, given that that involves thinking about X. And the only other logical possibility is that it involves the content of X existing in our mind as part of realitywhich is the mental state of believing X.

So even deliberately thinking X, like a mantra, inherently involves believing X. Also, our memory ensures that this inclusion of the content of X into our understanding of reality continues beyond thinking X.

As I mentioned, this can seem obviously contrary to our experience. Again, it can, for example, seem obvious that if we believe that David isn’t vegetarian, then we won’t reverse that belief simply by deliberately thinking the claim David is vegetarian, like a mantra. However, immediately after deliberately thinking David is vegetarian we’ll be aware that we were just then thinking David is vegetarian not because we've any reason to believe that David is vegetarian, but solely because we decided to think the claim, like a mantra, despite believing the opposite. And given the speediness of the brainwhich works on the timescale of milliseconds – that awareness will lead us to think/believe David isn't vegetarian within a fraction of a second of us thinking/believing David is vegetarian. Therefore although we believe that David is vegetarian upon thinking the claim David is vegetarian, and that belief lasts beyond that thinking, it only does so for a fraction of a second, and so we’ll normally have no subsequent awareness of it.

We may also deliberately think X, like a mantra, when we don’t believe either it or even a contrary claim immediately before doing so. Immediately after doing so we’ll be aware that we were just then thinking X not because we've any reason to believe X, but solely because we decided to think X, like a mantra, despite having a lack of belief regarding the subject of X. And given the speediness of the brain, that awareness will lead us to think/believe a claim that expresses our uncertainty about the subject of X within a fraction of a second of us thinking/believing X. Therefore our belief of X will still only last for a fraction of a second, and we’ll therefore still normally have no subsequent awareness of it.

The fact that deliberately thinking X, like a mantra, inherently involves believing X explains the attraction of self-help mantras. For example, consider someone with low self-esteem repeating the mantra ‘I’m a lovable person’. For as long as they maintain a level of focus on this task that prevents them from having any contrary thoughts they’ll believe this claim, thereby giving them, albeit temporarily, the higher self-esteem that they crave. And that temporary increase in self-esteem can lead to the misplaced hope that regular sessions of this practice will, on its own, eventually lead to an enduring higher self-esteem.

Our extreme credulity

Now consider the entrance of a claim into our mind. As I stated in chapter 1, a claim enters our mind via one of four mental processes:

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

    • reasoning – when we generate the claim using logic, whether good or bad

    • imagination – when we generate the claim without using logic

    • recollection – when we remember the claim.

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. Therefore the entrance of X into our mind must consist of us either thinking X or thinking about X. But can it be either, or are we always thinking X, or always thinking about X, upon X entering our mind? First consider thinking about X.

Again, thinking about X can involve us either contemplating X or thinking a claim about X. For example, thinking about the claim David is vegetarian can involve us either contemplating this claim or thinking a claim such as Amy said that David is vegetarian.

However, claim Y about X can’t enter our mind until after X has entered our mind, regardless of which mental process Y enters our mind by. That is, given that X is part of Y, we comprehend X during the process of comprehending Y, and we consider X during the process of generating Y with our reasoning or imagination, and we recall X during the process of recalling Y. Although, given the speediness of the brain, Y can enter our mind within a fraction of a second of X doing so, and so it can seem that these two mental events are the same event.

Therefore the question of whether the entrance of X into our mind can involve us either thinking X or thinking about X, or only ever involves us doing one of these, is only concerned with thinking about X in the sense of contemplating X. And it’s this sense that I mean when I subsequently refer to thinking about X, unless I state otherwise.

Also, it might be thought that the process of comprehending X involves, by definition, thinking about X. However, it actually involves the language areas of our brain analysing – via our senses – speech sounds or textual symbols, or whatever is communicating X, in order to try to recreate it. We aren't able to contemplate X until X has entered our mind upon being recreated. Therefore the process of comprehending X only involves thinking 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 contemplate the part that we’ve comprehended so far. But contemplating X itself obviously requires us to comprehend the whole claim.

Now consider that thinking about X is itself a mental process, given that contemplating X involves mentally processing X. Any process, whether mental or physical, involves the processing of the input to the process to produce an output:

For example, the process of book manufacturing involves the processing of paper and ink, and other inputs to this process, to produce books. In the case of thinking about X, the main input to this process is X – the other inputs being relevant parts of our knowledge – and any output is some conclusion about X.

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

For example, the inputs to the process of book manufacturing, such as paper and ink, are the outputs of other processes. In the case of thinking about X, the main input to this processXis the output of the mental process of either reasoning, imagination, comprehension, or recollection:

The outputting of X by the first process and the processing of X by the second are obviously different events, given that the outputting of X and processing of X are different kinds of events, involving different processes. But the outputting of X by the first process is the entrance of X into our mind, whereas the processing of X by the second process is the process of thinking about X. Therefore, the entrance of X into our mind and thinking about X are actually inherently different events. That is, the entrance of X into our mind can't itself ever consist of thinking about X.

It might be objected that, even though the outputting of X by the first process and the processing of X by the second process are different events, the completion of the first process could still be the beginning of the second. That is, the entrance of X into our mind, upon being outputted by the first process, could be the entrance of X into the process of thinking about X.

Consider the following analogy. When someone walks through a doorway connecting two adjacent rooms, their crossing of the threshold is both their exiting from one room and their entering into the other. Therefore, even though exiting a room is the opposite of entering a room, they can be the same event. Similarly, even though outputting is the opposite of inputting, the outputting of X from the first process could also be the inputting of X into the second.

However, first, the person walking through the doorway actually isn't analogous to the two consecutive processes. Although walking involves innumerable processes inside our body, the person's walking out of the first room doesn't involve them being outputted by some process, and their walking into the second room doesn't involve them being inputted into some process. Therefore the person exiting from the first room and entering into the second isn't analogous to the outputting from the first process and inputting into the second.

And unlike that exiting and entering, that outputting and inputting can't be the same event. Consider the output of a process becoming an input to another after a time gap. The outputting from the first process doesn't itself also involve the inputting of something into a process. And the inputting into the second process doesn't itself also involve the outputting of something from a process. And if outputting and inputting can each occur without itself also involving the other, then outputting and inputting are different kinds of events. Indeed, whereas the completion of a process involves that processing stopping, because it's finished, the beginning of a process involves that processing starting. And processing starting and processing stopping are inherently different kinds of events. And different kinds of events can't, by definition, ever be the same event. Therefore, the outputting of X from the first process can't itself also be the inputting of X into the second – although these two events can, in theory, be immediately consecutive.

Regarding the person exiting from the first room and entering into the second, these are merely different perspectives of the same event – the person walking through the doorway – rather than different kinds of events. A person exiting from any space also involves, in itself, their entering into another space. And a person entering into any space also involves, in itself, their exiting from another space. Therefore, unlike outputting and inputting, exiting and entering can't each occur without itself also involving the other. Even when someone walks from one room to another via a corridor, their exiting from the first room is also their entering into the corridor, and their entering into the second room is also their exiting from the corridor. Even when someone walks out of a building, their exiting from the building is also their entering into the area immediately outside.

So the completion of the first process can't itself be the beginning of the second. That is, the entrance of X into our mind, upon being outputted by the first process, can't itself be the entrance of X into the process of thinking about X.

It might then be objected that, even though the completion of the first process can't itself be the beginning of the second, the entrance of X into our mind could still be the entrance of X into the process of thinking about X. That is, perhaps, upon X being outputted by the first process, it doesn't actually enter our mind until it enters the second process, just as the content of a memory doesn't enter our mind until it's part of our current thinking.

However, the outputting of X from the first process is the entrance of X into our mind as a matter of definition. For example, the outputting of X from the process of reasoning is, by definition, a conclusion, and concluding X involves, by definition, the entrance of X into our mind. Likewise, comprehending X, imagining-up X, and recalling X, all involve, by definition, the entrance of X into our mind.

It's possible that upon X being created, recreated or retrieved by the first process it must then be transmitted to some central processing area of the brain in order to enter the mind. But if so then that would merely mean that that transmission of X is the last stage of the first process, given that the outputting of X from that process is, by definition, the entrance of X into our mind. And, as I explained, that outputting of X from the first process can't also be the inputting of X into the process of thinking about X.

It might then be objected that even though comprehending X, for example, involves, by definition, the entrance of X into our mind, this moment could still be the entrance of X into the process of thinking about X. For example, perhaps our understanding of our comprehension of a claim is wrong, and it doesn't consist solely of the first process, but also of the entrance of the output of that process into the second process. And likewise for X entering our mind via our reasoning, recollection or imagination.

However, consider that comprehending X is a mental task.

The performance of any kind of task – whether by our minds, or our minds and bodies, or a machineconstitutes a single process. That is, the beginning of the performance of the task is the beginning of that process, and the completion of the task is the completion of that process. The performance of the task may involve the performance of sub-tasks, with such activities therefore constituting sub-processes. And the task may itself be a sub-task of another process, with the performance of the task therefore itself constituting a sub-process. But in either scenario the performance of the task as a whole constitutes a single process, even if it involves sub-processes or constitutes one.

So our performance of the mental task of comprehending X constitutes a single process, with our completion of this task therefore being the completion of this process. Therefore our comprehension of X can't consist of the first process and the beginning of the second. That wouldn't constitute a single process, and the completion of the task would be the beginning, rather than the completion, of a process. Therefore our comprehension of X must indeed consist solely of the first process, with our completion of this taskthe entrance of X into our mind – therefore indeed being the completion of this process. And the same logic applies to X entering our mind via our reasoning, recollection or imagination.

So the entrance of X into our mind, which is the outputting of X by the first process, indeed can't itself consist of us thinking about X. And, as I stated above, if X exists in our mind then we must be either thinking X or thinking about X, given that there’s no other possibility. Therefore the entrance of X into our mind must always consist of us thinking X. Indeed, thinking X is the outputting of X from a mental process – that is, thinking X doesn't itself involve mentally processing X, although that may begin immediately after thinking X.

Regarding reasoning, to conclude X is, by definition, to think X. But the idea that the entrance of X into our mind via comprehension, recollection, or imagination doesn't consist of is thinking about X, and instead consists of us thinking X, can seem obviously contrary to our experience. However, given the speediness of the brain, 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 it entering our mind.

The conclusion that the entrance of X into our mind must always consist of us thinking X leads to an even more counterintuitive conclusion. The analysis in the previous two sections showed that to think X is always to believe X. Therefore, the mere entrance of a claim into our mind, whether via reasoning, comprehension, imagination or recollection, causes us to believe it. And our memory ensures that this inclusion of the content of the claim into our understanding of reality continues beyond the claim's entrance into our mind. I call this theory of belief formation credulism, given its extreme claim about our credulity.

As I mentioned in chapter 1, credulism can initially seem not just counterintuitive, but unbelievable, which can itself seem to disprove it. The theory can seem obviously contrary to both the concept and experience of comprehending a claim, or recalling one, or generating one with our imagination. Regarding reasoning, a conclusion is by definition a belief. However, it can seem obviously contrary to both the concept and experience of reasoning 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. I address these points in the next two sections.

Credulism is counterintuitive in another way. The above theoretical argument consists solely of conceptual analysis – that is, it doesn't at any point depend on observational evidence. And the argument is a continuous chain of logical implication. It therefore shows not only that this is how beliefs form, but also that this is so not because of the nature of the human brain, but simply by logical necessity.

Again, the central tenet of the field of psychology today is that how the human mind works is solely due to the wiring and chemistry of the human brain, which is in turn determined by a person’s genes and experiences. Therefore all mainstream theories about any aspect of the functioning of the human mind involve that aspect being due, in some way, to the nature of the human brain. However, although our capacity for belief is obviously due to the nature of the human brain – rocks can't form beliefs – there isn’t anything about the human brain which causes our extreme credulity. Instead, that extreme credulity is simply a logically inherent, and therefore inevitable, feature of a claim entering a mind, for any form of intelligence. And so the current understanding of belief formation is actually logically impossible.

The logical necessity of credulism, and of the certainty of belief, and of their implications for our psychology, implies a distinction between human nature and human psychology. That is, human nature is those universal aspects of our psychology that are due to evolution by natural selection, whereas human psychology is the combination of human nature and those universal aspects of our psychology that are due to logical necessity.

Credulism and comprehension, recollection, and imagination

Again, credulism can seem obviously contrary to both the concept and experience of comprehending a claim, or recalling one, or generating one with our imagination. However, consider comprehending a claim.

The concept of comprehending a claim doesn't involve the claim being believed – it simply involves the claim being understood. But this doesn't mean that, when we comprehend a claim in practice, the entrance of the claim into our mind can't cause us to also, and simultaneously, believe the claim. Therefore, credulism actually isn't contrary to the concept of comprehending a claim.

However, it can seem obvious from our experience of comprehending claims that the mere entrance of a claim into our mind doesn't cause us to believe it. For example, it can seem obvious from our experience of comprehending the obviously false claim Paris is the capital of Germany that this doesn't involve believing it.

But it’s important to bear in mind two things. First, credulism doesn’t state that our belief of a claim, upon it entering our mind, is indefinite. Second, again, the brain works on the timescale of milliseconds. Therefore, when we comprehend a claim that we don’t already believe, and we thereby believe it, this belief can cease within a fraction of a second of forming, and we’ll therefore then normally have no subsequent awareness of it.

I explained earlier that when we deliberately think claim X, like a mantra, without believing X before doing so, our resulting belief of X will cease within a fraction of a second of forming, and we’ll therefore then normally have no subsequent awareness of it. Our belief ceases so quickly because immediately after deliberately thinking X we’re aware that we were thinking X just then not because we've any reason to believe X, but solely because we decided to think X, like a mantra, despite either believing a contrary claim or having a lack of belief regarding the subject of X.

In the case of comprehending/thinking X, we think X not because we decided to think X, like a mantra, but because comprehending X involves thinking X. Indeed, X may enter our mind for the first time upon comprehending it, and so our comprehending/thinking X couldn't then be preceded by a decision to think X. Also, as I explained, we're normally not even aware that we're thinking X upon comprehending X, because comprehending X seems to involve thinking about X.

However, consider comprehending an obviously false claim, such as the above Paris is the capital of Germany. Although we'll believe this claim upon it entering our mind, its obvious falseness means that that belief only lasts the fraction of a second that it takes our reasoning to generate the contrary claim Paris isn’t the capital of Germany. This reasoning will involve recognising that the claim Paris is the capital of Germany is contrary to the web of consistent beliefs which make-up our understanding of reality – specifically, beliefs such as Paris is located in France, Paris is the capital of, and only of, France, and Berlin is the capital of Germany. And given the extreme briefness of our preceding belief, we'll normally have no subsequent awareness of it.

And the same applies to comprehending a claim that merely seems obviously uncertain. For example, even if the claim It'll rain tomorrow seems obviously uncertain, our comprehension of it will involve believing it. But that belief will be replaced within a fraction of a second, via our reasoning, by our belief of the claim It's uncertain that it'll rain tomorrow. And we'll therefore normally have no subsequent awareness of our extremely brief preceding belief.

Of course, we also comprehend claims that don’t seem obviously false or even obviously uncertain. For example, upon hearing someone mention that they went to the cinema the previous evening, this claim may not seem obviously false or even obviously uncertain. Credulism implies that if we don't already believe such a claim then we'll believe it upon comprehending it. And that belief won't be ended by disbelief or doubt within a fraction of a second of forming. It might therefore be objected that such a belief would last long enough for us to be aware of it, and thus also aware that our mere comprehension of the claim involved believing it. However, there are several reasons why we tend not to be aware of the latter.

First, given the certainty of belief, we tend not to be motivated to consider the formation of our beliefs – even beliefs formed in the immediate past. And, by definition, we can't become aware of our credulity regarding a comprehended claim if we don't consider the formation of that belief. In fact, the certainty of belief means that we tend not to even think about our beliefs as beliefs. That is, given the certainty of belief, we tend to be thinking solely about the apparent reality that is the content of our beliefs, rather than also thinking about our belief of that content. These points explain why it’s normally easier for us to notice other people’s credulity than it is for them, or than it is for us to notice our own credulity: observing someone else forming a belief involves, by definition, thinking about the belief as a belief, and about how it forms.

Second, we’re usually so cognitively busy that it tends not to occur to us to consider the formation of our beliefs – even beliefs formed in the immediate past. Even our basic waking cognitive activity involves continuously trying to work-out:

  • what's happening in the present, whether in our immediate surroundings or beyond, and often including the contents of other people’s minds

  • why it's happening

  • what's likely to happen in the immediate future, whether in our immediate surroundings or beyond, and often including the contents of other people’s minds

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

  • how best to act in the immediate future in order to achieve our goals, possibly including what to say.

And this cognitive activity involves a constant stream of belief formation.

Of course, the more cognitively busy we are the less likely we'll consider the formation of our beliefs. And our degree of cognitive busyness increases as the following factors increase:

  • time pressure

  • the amount of information being processed

  • the difficulty of the 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 claims that would normally seem obviously false, or at least obviously uncertain, our belief of them can last for more than a fraction of a second, and until our level of cognitive busyness has reduced.

In addition to these two main reasons why we tend not to consider the formation of our beliefs, we’re also less likely to do so the more time that has passed since the belief formed – given the decreasing prominence of this event in our mind – or the more mundane its subject – given the decreasing significance of whether the belief is true.

Also, even when we cease holding a belief, we don’t automatically analyse how that belief formed. And even if we do analyse the formation of one of our beliefs, past or present, we may not remember how it formed. And even if we do remember that it formed when we comprehended the claim concerned, we may assume that our belief was the product of some reasoning, however brief, which immediately followed the claim’s entrance into our mind. For example, we may assume that we only believed the claim upon considering that we trust its source.

The above analysis of credulism and the concept and experience of comprehending a claim similarly applies to recalling a claim and generating one with our imagination. Therefore, even when we’re aware of our credulity upon a claim entering our mind via one of these processes, we’re unaware that the entrance of a claim into our mind always involves believing it. And we therefore disbelieve credulism within a fraction of a second of comprehending it for the first time, and thereby, ironically, seem to disbelieve credulism upon comprehending it, even though we believe it in that moment.

Credulism and reasoning

Credulism can also seem obviously contrary to both the concept and experience of reasoning. Consider first the concept of reasoning.

Again, although a conclusion is by definition a belief, it can seem also true by definition that our belief of this claim upon it entering our mind is due to the claim being the product of our reasoning. But if the mere entrance of a claim into our mind causes us to believe it, then our belief of a claim upon it entering our mind via our reasoning is due merely to that entrance.

Consider that reasoning involves determining an apparent logical implication of particular premises. For example, a logical implication of the premises Vegetarians don’t eat meat and Pork sausages contain meat is Vegetarians don't eat pork sausages. And although reasoning is the formation of beliefs using logic, the task of determining an apparent logical implication of particular premises isn't itself concerned with the reality of the content of either those premises or an apparent logical implication of them, but is merely concerned with what follows logically from those premises. According to the current conception of reasoning, we believe an apparent logical implication upon it entering our mind because we believe its premises as well as the validity of our logic.

But the implication of credulism is that our belief of an apparent logical implication upon it entering our mind is due merely to that entrance. It's of course true by definition that, when we form a conclusion, our reasoning led to the formation of this belief, and that belief formation occurred upon the claim being generated by that reasoning. But we incorrectly infer from this that it's also true by definition that our belief of the claim upon it entering our mind was due to the claim being the product of that reasoning. In short, the implication of credulism is that the current conception of reasoning is wrong.

To be clear, credulism doesn't imply that, when we form a conclusion, our belief of the validity and premises of our logic is irrelevant to the formation of this belief. Again, by definition, our reasoning led to the formation of the conclusion. That is, 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 necessary for us to apply it to our premises. And the application of our logic to our premises led to the entrance into our mind of the claim that we thereby believed. The implication of credulism is that our belief of this apparent logical implication upon it entering our mind is due not to these beliefs about our premises and logic, but merely to that entrance.

Now consider the experience of reasoning. It can also seem from our experience that, when we form a conclusion, our belief of this claim upon it entering our mind is due to the claim being the product of our reasoning. However, it actually wouldn't make any difference to our experience of forming a conclusion whether our belief of the claim upon it entering our mind is due to the claim being the product of our reasoning or the mere entrance of the claim into our mind. That is, either way, what we actually experience is the same thing: the formation of a belief via reasoning. The apparent experience of this belief formation being due to the claim being the product of our reasoning is actually just our interpretation of this event.

However, credulism implies that we'll even believe a claim, that we don't already believe, upon it entering our mind via logic that we either believe is invalid or possibly invalid, or that is based on premises that we disbelieve or are uncertain about. For example, illustrating a logical fallacy involves deliberately applying invalid logic to particular premises. And hypothetical, 'What if...', reasoning involves determining an apparent logical implication of premises that we either disbelieve or are uncertain about. In such cases, the conclusion of our reasoning is either of the form The illogical [or possibly illogical] implication of the premises is X or of the form A logical implication of the false [or uncertain] premises is X. But although our conclusion isn't simply X, we also believe X upon it entering our mind in the process of reaching this conclusion.

The idea that we believe X upon it entering our mind via logic that we either believe is invalid or possibly invalid, or that is based on premises that we disbelieve or are uncertain about, can seem just as obviously contrary to experience as the idea that merely comprehending or recalling a claim, or generating one with our imagination, involves believing it. However, given our belief about the validity or premises of the logic, our belief of X ceases within a fraction of a second of forming. And we'll therefore normally have no subsequent awareness of this extremely brief belief.

So not only, as I explained in chapter 3, is it not true that we believe X because we’ve assessed that X is true, it’s not even true that we believe X because X was the product of our reasoning – even though both theories can seem true by definition and therefore unimpeachable. Instead, we believe X merely because X has entered our mind, whether via reasoning, comprehension, imagination or recollection.

Another possible objection

It might also be objected, regarding comprehending a claim that we don't already believe, that it's both obvious from experience and true by definition that our level of trust in the source of the claim affects whether we believe it, contrary to credulism. However, as I mentioned earlier, if we're aware that we formed one of our beliefs, past or present, when we comprehended the claim concerned, then an unawareness of credulism can lead us to assume that we believed the claim because we trusted its source. Also, if we distrust the source of a claim then our belief of the claim upon comprehending it will cease within a fraction of a second of forming, and we’ll therefore then normally have no subsequent awareness of it. Therefore it can seem that our distrust of the source prevented our belief of the claim. Our level of trust in the source of a comprehended claim affects not whether we believe it upon comprehending it, but whether we continue to believe it after comprehending/believing it.

However, there's one way that trusting the source of a comprehended claim can lead to our belief of it. If we cease believing a claim after comprehending it, for whatever reason, but subsequently conclude that we trust its source, then, as I explained in chapter 3, that trust can lead us to conclude that X is true, and thereby believe X. As I also explained in chapter 3, although we don't believe something because we’ve assessed that it’s true, concluding that X is true on the basis of our trust of its source doesn't actually constitute an assessment that X is true, given that our conclusion is based on a consideration of the source of X rather than on a comparison of X and reality.

The above analysis similarly applies to recalling comprehending a claim, if we also recall its source.

Why credulism matters

If merely comprehending or recalling a claim, or generating one with our imagination, involves believing it, and that belief can endure for any length of time, then that obviously has profound implications for human psychology and therefore our lives.

Also, I explained in chapter 4, the certainty of belief means that not only do we believe any claim upon it entering our mind, via any process, we always do so without any doubt. If degrees of belief were possible then our belief of a claim upon it entering our mind could at least be an uncertain belief, and that uncertainty could motivate us to investigate the truth of our new belief. Also, confirmation bias means that we're biased towards interpreting, seeking, and remembering information in a way that confirms, or helps to confirm, our new belief.

And as I also mentioned in chapter 4, and will show in later chapters, these two theories about the psychology of belief together provide a unifying explanation of all cognitive biases, and therefore of the whole of human irrationality.

As I've explained previously, given that belief is the centre of human psychology, the theory of credulism, together with the theory of the certainty of belief, will revolutionise the field of psychology. And this will in turn have equally profound implications for every aspect of our lives.

As I mentioned in chapter 1, the idea that the mere entrance of a claim into our mind causes us to believe it was first proposed by the prominent 17th-century philosopher Baruch Spinoza in his 1677 book Ethics.

Spinoza and the title page of his book Ethics

I also mentioned in chapter 1 that the most prominent modern academic writing on Spinoza’s theory is a 1991 paper called ‘How Mental Systems Believe’, which catalogues observational evidence, including experimental research, which seems to support the theory, and which I’ll cover in a later chapter. It was written by the Harvard psychology professor Daniel Gilbert, one of the rare academics who supports the theory.

Gilbert’s paper

However, Gilbert misunderstands Spinoza’s theory in one significant way: he thinks that it only applies to claims entering our mind via comprehension. This mistake is also made by the authors of most other articles and books which refer to the theory. In many cases, it seems that this is because the author based their understanding of the theory on either Gilbert’s paper or a paper or book written by someone who based their understanding of the theory on Gilbert's paper. For example, the psychology professor James Alcock, who’s an expert on belief, misrepresents the theory in this way in his 2018 book on belief, Belief that I referred to in chapter 1 citing Gilbert’s paper.

Strangely, there doesn’t seem to be an awareness within either psychology or philosophy of the profound, and revolutionary, implications of Spinoza's theory – not just among those who are aware of it but don’t support it, but even among the very few who do support it. This will be partly due to the strange unawareness in academia, that I mentioned in chapter 1, that belief is the centre of human psychology, and also to the common misunderstanding that the theory only applies to claims entering our mind via comprehension.

Although, even after taking these two points into account, the failure to appreciate that such an extraordinary theory has extraordinary implications is still very odd. That is, even if one is unaware that belief is the centre of human psychology, it's obvious that belief is central to human psychology, albeit alongside other aspects of human psychology. And even if one thinks that Spinoza's theory only applies to our comprehension of claims, it's obvious that we do this countless times during our everyday lives, for both written and spoken claims, however important or mundane.

One example of this significant underappreciation of the implications of Spinoza's theory is Alcock's above-mentioned book Belief. Even though Alcock is another one of the rare academics who supports the theory, he only spends about one and a half of the book's 638 pages on it, half-way through the book. And he merely introduces it, without considering even briefly the obvious and important question of why belief formation would work this way. And he doesn’t refer to it anywhere else in the book. As I mentioned in chapter 1, he doesn’t refer to belief being the centre of human psychology anywhere in the book. And, as I mentioned above, he only refers to Spinoza’s theory applying to comprehended claims.

And in the above-mentioned 1991 paper 'How Mental Systems Believe', Gilbert also doesn't refer to belief being the centre of human psychology, in addition to restricting Spinoza's theory to comprehended claims, and doesn't refer to the theory as having revolutionary, or even profound, implications. Indeed, Gilbert last published research on the theory in 1993, even though he's still an active researcher.

As I mentioned in chapter 1, the cognitive scientists Nicolas Porot and Eric Mandelbaum don't refer to belief being the centre of human psychology in their 2020 paper 'The science of belief: A progress report'. The paper refers to 'the centrality of belief to cognitive science', but also to belief having this position alongside other major aspects of psychology. They express support for Spinoza's theory, but it's unclear whether they appreciate that it doesn't just apply to comprehended claims. That is, they cite Gilbert's paper without criticising his misunderstanding of the theory, and the hypothetical scenarios they use to illustrate the theory only involve claims being comprehended.

Porot and Mandelbaum do claim that the theory can explain many different, and significant, psychological phenomena – including confirmation bias – but they don't claim that it has the potential to revolutionise psychology. Indeed, the part of this survey paper on the psychology of belief that deals with this fundamental aspect of belief consists of only five paragraphs – and doesn't consider even briefly the obvious and important question of why belief formation would work this way

The 2011 book The Believing Brain, by researcher and writer Michael Shermer, which I also referred to in chapter 1, ‘… synthesizes [his] thirty years of research …’ on the psychology of belief. Shermer states in the introduction ‘Beliefs come first, explanations for beliefs follow’ and ‘The brain is a belief engine’. Given these statements, and the book's title, it might be assumed that the book is all about Spinozan belief formation. Indeed, Shermer expresses support for Spinoza's theory in the book. However, he only refers to the theory in two paragraphs half-way through the book, and misunderstands it. And his thesis about belief formation is actually much less radical than Spinoza's.

In the introduction Shermer raises the question ‘Why do people believe?’, but his answer doesn’t mention that the mere entrance of a claim into our mind, whether via comprehension, reasoning, imagination or recollection, causes us to believe it, and that this is the cause of all belief formation. He instead just lists factors that influence what beliefs we form:

We form our beliefs for a variety of subjective, personal, emotional, and psychological reasons in the context of environments created by family, friends, colleagues, culture, and society at large ...

Indeed, in addition to thinking that Spinoza's theory only applies to comprehended claims, Shermer thinks that it merely states that we have a ‘tendency’ to believe – so not that we inevitably believe any claim that enters our mind – and that ‘belief comes quickly’ – so not immediately. Also, he doesn’t refer to belief being the centre of human psychology anywhere in the book. Given all of this, it isn't surprising that he doesn't refer to Spinoza's theory as having revolutionary, or even profound, implications.

Vindicating Spinoza

Spinoza tried to support his theory using an obscure theoretical argument that I can't wholly follow. It at one point refers to the geometry of a triangle, and at another point refers to an imaginary winged horse. According to this paper, several modern researchers have independently concluded that the argument doesn’t support its conclusion.

The essence of the argument seems to be that, logically, we can only think of a reason to disbelieve a claim after it has entered our mind and we’ve assessed it, and so we must believe the claim upon it entering our mind. However, not disbelieving a claim of course doesn't itself imply belief of the claim, given that it's possible to neither disbelieve or believe a claim.

The obscurity and apparent unsoundness of Spinoza’s argument partly explains why belief of his theory has, ironically, been negligible since it was published, and why most researchers in psychology and philosophy today haven’t even heard of it, and interest amongst those who have is low. One illustration of the current low status of the theory is that reference works on psychology or philosophy don’t refer to it, even briefly. For example, none of the over 1,700 entries in the online Stanford Encyclopedia of Philosophy refer to it – including the 14,000-word entry on belief and the 14,000-word entry on Spinoza. And neither do any of the almost 26,000 entries in the American Psychological Association’s Dictionary of Psychology. And neither do any of the philosophy or psychology textbooks that I’ve checked.

Another illustration of the current low status of Spinoza's theory is the 2018 book The Oxford Handbook of Spinoza, published by Oxford University Press. According to the blurb, it's a collection of essays written by ‘many of the world’s leading Spinoza specialists’, which ‘grapple directly with Spinoza’s most important arguments’. And the book is edited by Spinoza expert, and philosophy professor, Michael Della Rocca. However, none of the twenty-six essays in this 687-page book is on Spinoza's theory of belief formation, which is only mentioned briefly a few times, and the word ‘belief’ isn’t listed in the book’s extensive index.

In the previously-mentioned 1991 paper 'How Mental Systems Believe', Gilbert doesn’t outline Spinoza’s theoretical argument, or even refer to it, despite offering an alternative theoretical argument. This strange omission is perhaps due to him being unable to follow Spinoza’s obscure logic. Gilbert's speculative argument involves our comprehension of claims being Spinozan for an evolutionary reason, rather than logical necessity, and has several flaws, in addition to not addressing the implication of Spinoza's theory for claims entering our mind via reasoning, imagination and recollection.

He begins with the premise that to perceive something is to believe it. For example, to see a chair in front of us is to believe that there’s a chair in front of us. Therefore, such beliefs form before we’ve had a chance to reason about the content of the perception. He argues that we evolved to form such beliefs in this way because we often need to react quickly to our surroundings, and the content of our perceptions are a generally reliable representation of our surroundings. He then states that perception is therefore 'quintessentially Spinozan'.

Gilbert next suggests that our cognitive faculty could have evolved from our perceptual faculty, given that both involve mental representations. In the case of perception the mental representations are individual perceptions, and in the case of cognition they’re the content of individual claims. Also, both the perceptual process and the process of comprehending claims involve processing sensory data to create a mental representation – in the case of comprehension, we must perceive the medium used to communicate the claim, which is normally voice or text. Gilbert then suggests that the Spinozan nature of perception could therefore have been inherited by the process of comprehending claims. That is, just as to perceive something is to believe it, to comprehend claim X is to believe X.

He then argues that most people communicate true claims most of the time, quoting the philosopher Daniel Dennett: ‘The faculty of communication would not gain ground in evolution unless it was by and large the faculty of transmitting true beliefs’. Therefore, he 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 could allow us to immediately believe what we comprehend, and thereby react quickly to those claims.

However, first, although the biological value, and therefore evolution, of communication indeed depends on most communicated claims being true, the communication of false claims, knowingly or not, obviously isn't an infrequent occurrence. And given that our belief of false claims will tend to have negative consequences for us, from minor to major, it seems implausible that the frequency of true communicated claims is sufficient to lead to the evolution of our automatic belief of every claim that we comprehend. Indeed, the greater the credulity in our species, the greater the biological value of taking advantage of that credulity by lying, and therefore the greater the evolutionary pressure towards lying – and the greater the frequency of lying, the greater the evolutionary pressure away from credulity.

This point is used by the cognitive scientist Hugo Mercier in his 2020 book Not Born Yesterday, on gullibility, to argue that such credulous comprehension can't be true. But this argument 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, Mercier's reasoning is based on the previously-mentioned false premise that how the human mind works is solely due to the nature of the human brain.

In Not Born Yesterday Mercier argues against the idea that we're generally gullible, by using '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. However, ironically, if such cognitive mechanisms exist, this will actually be partly due to, rather than evidence against, our credulity. That is, given that the extreme credulity of Spinozan belief formation is logically unavoidable, but biologically costly, it could create an evolutionary pressure towards developing cognitive mechanisms that can somewhat counteract it.

Oddly, Mercier doesn't mention Spinoza's role in the origin of the idea that comprehending a claim involves believing it, despite the relevance of this idea to the subject of his book, and even though he cites Gilbert's paper, which does mention Spinoza's role. The fact that Mercier didn't think that it was worth mentioning such a basic fact about the history of this idea is perhaps another illustration of the idea's current low status.

A second problem with Gilbert's argument is that there's currently no theoretical basis, or evidence, for the idea that cognition evolved from perception. And a third problem is that the mental state of belief is obviously a fundamental cognitive state, and so the idea that perception is 'quintessentially Spinozan' – that to perceive something is to believe it – and the idea that cognition came after perception actually contradict each other.

A fourth problem with Gilbert’s argument is that if to perceive something is to believe it, then such beliefs form before we’ve had a chance to reason about the content of the perception. As I explained in chapter 3, the formation of beliefs about our surroundings via perception must involve at least some reasoning about the content of our perceptions – although, such reasoning is often so basic, and therefore fast, that such beliefs can seem to be a direct product of the perceptual process. Therefore, the starting point of Gilbert's argument, that perception is Spinozan, is false.

So Gilbert's alternative theoretical argument fails to vindicate Spinoza's theory in relation to our comprehension of claims, in addition to not addressing the implication of the theory for claims entering our mind via reasoning, imagination and recollection.

The argument that I present in this chapter does vindicate Spinoza's theory, and is the only other alternative theoretical argument that I'm aware of. The essence of the argument is surprisingly simple, considering its counterintuitive conclusion, and can be presented in just nine steps:

    1. There are two logically possible ways that the content of a claim, X, can exist in our mind: as the content of X and as part of reality.

    2. The former involves thinking about X.

    3. And thinking about X is different from thinking X.

    4. Therefore, thinking X must involve the content of X existing in our mind as part of reality – that is, thinking X always involves believing X.

    5. If X exists in our mind then we must be either thinking X or thinking about X, given that there’s no other possibility.

    6. Therefore, the entrance of X into our mind, whether via reasoning, comprehension, recollection or imagination, must consist of us either thinking X or thinking about X.

    7. However, the entrance of X into our mind is the outputting of X from a mental process, whereas thinking about X is the processing of X by a subsequent mental process.

    8. But thinking X is the outputting of X from a mental process – that is, thinking X doesn't itself involve mentally processing X, although that may begin immediately after thinking X.

    9. Therefore the entrance of X into our mind, whether via reasoning, comprehension, recollection or imagination, must always consist of us thinking/believing X.

As I explained in chapter 1, the past absence of a sound theoretical argument for this theory, and for the theory of the certainty of belief, is ultimately much more an effect, than a cause, of the poor status of these theories within academia. The more fundamental cause of that poor status is their counterintuitive nature, which has led most academics who’ve encountered them to not take them seriously, which has in turn resulted in academia not giving them sufficient attention to discover the sound theoretical arguments that do exist for them.

It's over 340 years since Spinoza published his theory. Such a long gap between the creation of a theory and its vindication is unusual in science, although that gap was even greater, much greater, for the theory that Earth goes around the Sun – heliocentrismrather than vice versageocentrism. The ancient-Greek astronomer Aristarchus of Samos presented the earliest known heliocentric theory. But acceptance of heliocentrism only began, and very slowly, eighteen centuries later, after the publication in 1543 of the book On the Revolutions of the Heavenly Spheres, by the mathematician and astronomer Nicolaus Copernicus. The book presented a mathematical model of heliocentrism that was reasonably compatible with the motions in the sky of the Sun, the Moon, the observable planets, and the stars. Acceptance of heliocentrism accelerated in the 17th century after this mathematical model was improved by the mathematician and astronomer Johannes Kepler, and astronomical observations by the scientist Galileo Galilei, using the newly-invented telescope, supported heliocentrism over geocentrism.

The title page of the first edition of Copernicus's On the Revolutions of the Heavenly Spheres, and a page of the book with a diagram of heliocentrism. The paragraph on the title page is the book's blurb, which ends 'buy, read, and enjoy'.

Copernicus's use of mathematics to reach a conclusion about nature, rather than merely using mathematics to describe the current understanding of nature, was controversial. Even in Galileo's time a professor wrote that '... anyone who thinks that he can prove natural properties with mathematical argument is simply demented... ' (source, chapter 5). However, this approach eventually became accepted as a legitimate means of furthering our understanding of nature. Today, the application of mathematics to develop and refine theories in physics is a whole branch of physics – theoretical physics – and this approach is fundamental to cosmology.

In the field of psychology today, using logic alone to reach conclusions about human psychology is considered unscientific, given the absence of observational evidence in such reasoning. However, given that credulism and the certainty of belief are due solely to logical necessity, they actually can only be explained by logic – and likewise for their profound implications for human psychology. Therefore using logic alone to reach conclusions about human psychology needs to become accepted as a legitimate means of furthering our understanding of human psychology, as happened with using mathematics to further physics and cosmology.

As I mentioned in chapter 1, although heliocentrism initially seemed obviously contrary to experience, closer analysis revealed that it isn't. Likewise, as this chapter and the previous showed, although credulism and the certainty of belief can initially seem obviously contrary to experience, closer analysis reveals that they aren't. Hopefully this fact, and the theoretical arguments presented in these two chapters, will, as happened with heliocentrism, lead to these two theories being taken seriously, and then being conclusively tested, and thereby to them finally being widely acceptedassuming they pass such tests, as the theoretical arguments imply they will.


The next chapter is in progress...

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