The theoretical argument for credulism

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This article is part of the 'core reading' series of articles:

The certainty of belief > Why belief can't be the product of an assessment of truth > The theoretical argument for credulism > Objections to credulism > The evidence for credulism


Summary: This article presents a counterintuitive new theory about how beliefs form, called 'credulism'. It shows that, as a matter of logic, and contrary to the common understanding, the mere entrance of a claim into our thought processes involves believing it, whether it does so via our comprehension, reasoning, imagination, or memory.

1 Introduction


'Credulism' is a counterintuitive new theory about how beliefs form[1]. It's an extension of a theory that was first proposed by the seventeenth-century philosopher Baruch Spinoza[2][3].

Consider first the difference, for any claim, X, between thinking X and thinking about X.

2 Thinking X versus thinking about X


  1. Thinking X consists solely of thinking about the subject of X.
    • For example, thinking 'There are eggs in the fridge' consists solely of thinking about the presence of eggs in the fridge.
  2. Thinking about X consists of thinking about this claim about the subject of X
    • For example, thinking about the claim 'There are eggs in the fridge' consists of thinking about this claim about the presence of eggs in the fridge.
    • This will consist of either contemplating the claim, or an outcome of that contemplation - that is, a specific thought about the claim, such as 'It isn’t true that there are eggs in the fridge'.
  3. Therefore, thinking X is different from thinking about X.
    • The exception to this point are self-referential claims, like 'This is a sentence' and 'This claim is true'. However, our belief of such claims, while possible, obviously has no utility, and so we normally don't store them in our long-term memory. And the existence of such claims doesn't undermine the logic of this chain of reasoning regarding non-self-referential claims.
  4. And two different thoughts cannot occur simultaneously.
  5. Therefore, we can't be simultaneously thinking X and thinking about X.
    • Of course, either can occur immediately after the other. Also, either can occur part-way through the other, but this must involve the other ceasing.


Now consider the two ways in which the content of a claim can exist in our thought processes.

3 X as a claim versus X as reality


  1. To believe X isn't, in itself, to believe that X is true: believing that X is true involves having a belief about X, whereas believing X does not, and solely involves having a belief about the subject of X.
    • For example, believing that the claim 'There are eggs in the fridge' is true involves having a belief about this claim - that it has the property of being true - whereas believing that there are eggs in the fridge doesn't, and solely involves having a belief about the presence of eggs in the fridge - that there are indeed eggs in that fridge.
  2. To believe that X is true is, by definition, to believe that the content of this claim matches reality.
  3. Therefore, if we believe that X is true, then thinking 'X is true' involves the content of X existing in our thought processes as both the content of a claim and reality.
  4. If we believe X, then thinking X can't involve the content of X existing in our thought processes as the content of a claim, because we're not thinking about this claim, but solely about its subject.
    • For example, if we believe that there are eggs in the fridge, then thinking 'There are eggs in the fridge' can't involve the content of this claim existing in our thought processes as the content of a claim, because we're not thinking about the claim 'There are eggs in the fridge', but solely about the presence of eggs in the fridge.
  5. Therefore, if we believe X, then thinking X involves the content of X existing in our thought processes solely as reality.
    • In the example, if we believe that there are eggs in the fridge, then thinking 'There are eggs in the fridge' involves the presence of eggs in the fridge existing in our thought processes solely as reality.
  6. If we believe either that X is false, or that there isn't enough information to decide whether X is true or false, then our thinking involved in our non-belief of X involves the content of X existing in our thought processes solely as the content of a claim.
  7. In sum, the content of a claim can exist in our thought processes solely as the content of a claim, or solely as reality, or as both.


Now consider the relationship between thinking and believing.

4 To think X is to believe X


To think X is to believe X. For example, to think 'There are eggs in the fridge' is to believe that there are eggs in the fridge. But thinking about X obviously doesn't necessarily involve believing X. For example, whereas thinking that X is true involves believing X, simply contemplating X, or thinking that it's false, doesn't.

It might be objected that although believing X necessarily involves thinking X, thinking X doesn't necessarily involve believing X. If it did, then we'd believe any claim just by thinking it, mantra-like, which obviously doesn't happen. For example, if we believe that there aren't eggs in the fridge, then we'll not believe otherwise simply by thinking, mantra-like, the claim 'There are eggs in the fridge'.

However, as a matter of logic, thinking X actually does necessarily involve believing X. Consider the following chain of reasoning:

  1. The content of a claim can exist in our thought processes solely as the content of a claim, or solely as reality, or as both.
  2. If the content of X exists in our thought processes as the content of a claim, then we're thinking about X.
  3. We can't be simultaneously thinking X and thinking about X.
  4. Therefore, as we're thinking X, the content of X must exist in our thought processes as reality.
  5. And if the content of X exists in our thought processes as reality, then, by definition, we believe X.
  6. Therefore, as a matter of logic, to think X is to believe X, whether or not we believed X immediately before doing so.
  7. Also, the existence of the content of X in our thought processes as reality involves that content being stored as such in our short-term memory, and then possibly our long-term memory.
  8. Therefore, when we think/believe X, our belief doesn't merely last the duration of this thought.


It may seem that this conclusion is obviously contrary to our experience, and so can't be true. That is, we don't seem to believe a claim simply by thinking it, mantra-like. However, although our belief of X, upon thinking X, doesn't merely last the duration of that thought, it can, given the speed of the brain, cease within a further fraction of a second, and we'll then likely have no recollection of it.

Consider the above example of thinking, mantra-like, and contrary to our immediately preceding belief, 'There are eggs in the fridge'. Although we'll thereby believe this claim, we'll then, within a further fraction of a second, recall that we were thinking this claim solely because we chose to do so, mantra-like, and contrary to our immediately preceding belief, and therefore not because we've any reason to change that belief, and we'll therefore then again think/believe 'There aren't eggs in the fridge'. And because our belief in the presence of eggs in the fridge was so brief, we'll likely have no recollection of it.

Our belief of X upon thinking X, whether or not we believed X immediately before doing so, explains the attraction of self-help mantras. For example, if someone with low self-esteem repeatedly says, and therefore also thinks, 'I’m a lovable person', and they can maintain sufficient focus on performing this task so that they're prevented from having any contrary thoughts, then they'll believe this claim for as long as they do so, thereby giving them, albeit temporarily, the increased self-esteem that they crave. The effect is always temporary because this practice doesn't address whatever is causing their low self-esteem. However, the temporary increase in self-esteem often leads to the misplaced hope that regular sessions of this practice will eventually lead to an enduring increased level of self-esteem, just as repeated exercise of a muscle increases its strength.

Now, finally, consider how claims enter our thought processes.

5 Our complete credulity


  1. The content of any belief is a claim, whether profound - for example, 'There's an afterlife' - or mundane - for example, 'There are eggs in the fridge'.
  2. And any claim, X, enters our thought processes as the output of one of four possible mental processes: it can be comprehended via our senses - whether X was spoken or written - or created via our reasoning or imagination, or recalled via our memory.
  3. And if X exists in our thought processes, then we must be either thinking X or thinking about X.
  4. Therefore, the output of the process by which X enters our thought processes must be either the thought 'X' or the process of thinking about X.
    • To be clear, the process by which X enters our thought processes isn't itself that of thinking about X: whereas the former process involves, by definition, X existing in our thought processes only at the very end, the latter involves, by definition, X existing in our thought processes throughout. Even comprehending a claim, whether spoken or written, doesn't involve thinking about it, but involves the language areas of our brain analysing whatever is communicating it - speech sounds, text, etc. - in order to recreate it.
  5. Every process has an input and output, and an output of one process can be an input to a subsequent process.
  6. X is of course an input - the main input - to the process of thinking about X, but the process by which X is created, re-created, or recalled, and thereby enters our thought processes, isn't.
    • Of course, information about the process by which X entered our thought processes may be an input to the process of thinking about X, even if that first process itself isn't.
  7. Therefore, the main input to the process of thinking about X is the output of the process by which X enters our thought processes.
  8. Therefore, the output of the process by which X enters our thought processes isn't itself the process of thinking about X, but the main input of that process.
  9. Indeed, although the output of a process may be the input to an immediately subsequent process, it can't itself be another process:
    1. If the output of a process was itself another process, then the first process would likewise be an input to the second.
    2. And, by definition, the input to a process is processed by that process to produce the output of the process.
    3. However, a process is a sequence of events, and a sequence of events isn't something that can be processed.
      • Of course, information about a sequence of events may be processed, even if the sequence itself can't be.
    4. Therefore, the output of a process can't itself be a process.
  10. And although the thought 'X' will be part of a thought process, it isn't itself a process - that is, it doesn't itself involve the processing of an input to produce an output - and is simply the output of a process.
  11. Therefore, as a matter of logic, the output of the process by which X enters our thought processes is the thought 'X', with the process of thinking about X possibly occurring, if at all, after X has entered our thought processes.
    • While it may seem unsurprising that we're thinking X upon X entering our thought processes as the product of our reasoning, it's surprising that we're thinking, rather than thinking about, X at the moment that it enters our thought processes via our comprehension, imagination, or memory.
  12. And, also as a matter of logic, to think X is to believe X.
  13. Therefore, as a matter of logic, the mere entrance of a claim into our thought processes involves believing it, whether it does so as the product of our comprehension, reasoning, imagination, or memory.
  14. Also, our belief of X involves its content being stored as reality in our short-term memory, and then possibly our long-term memory.
  15. Therefore, when we think/believe X upon it entering our thought processes, our belief doesn't merely last the duration of this thought.


This conclusion is obviously contrary to the common understanding about how beliefs form. According to that understanding, we're able to comprehend, or recall, a claim, or generate one using our imagination, without necessarily believing it. If we don't already believe such a claim, then we'll only do so after it has entered our thought processes, upon us assessing it to be true. And even regarding our belief of a claim that's the product of our reasoning, the implication of the above is counterintuitive.

Reasoning involves trying to determine the logical implications of certain premises. However, determining logical implications isn't itself concerned with the truth of either the premises or their apparent logical implications, but is simply concerned with what follows logically from those premises. For example, a logical implication of the claims 'All cats are mammals' and 'All mammals are warm-blooded' is 'All cats are warm-blooded', and all of these claims are true, but the validity of this logic is independent of that truth. That is, it's equally valid to conclude that the claims 'All cats are poets' and 'All poets are vegetarian' logically imply that 'All cats are vegetarian', even though all of these claims are false.

According to the above argument, we believe all apparent logical implications that we determine, and merely because they've entered our thought processes, contrary to the common understanding that we can determine logical implications without necessarily believing them. According to that understanding, our belief of apparent logical implications depends on our belief of not just the validity of the logic, but also its premises. Therefore, the common understanding that when we infer X from premises that we believe, we believe X because X is the conclusion of that reasoning is actually the wrong way around: X is the conclusion of our reasoning because we believe X upon it entering our thought processes. That is, although X is a product of our reasoning, as we try to determine the logical implications of claims that we believe, our belief of X is not, but is simply a product of it entering our thought processes.

The theory that our mere comprehension of a claim, whether written or spoken, involves believing it was first proposed by Spinoza. The 1991 article 'How Mental Systems Believe'[3], by the psychologist Daniel Gilbert, covers the history of Spinoza’s theory, and catalogues empirical support for it. But whereas Gilbert speculates that the origin of our credulous comprehension might be evolutionary, the above chains of reasoning show that it's simply logically necessary. And the above chains of reasoning not only provides a theoretical vindication of Spinoza’s theory, but also extends it to claims entering our thought processes via any process, whether comprehension, reasoning, imagination, or remembering. This counterintuitive new theory about how beliefs form is called 'credulism', given its claim of our complete credulousness.

The article Objections to credulism addresses the contrast between credulism and the common understanding of how beliefs form.


6 Sources

  1. The following argument first appeared, in a less advanced form, and along with earlier versions of other parts of this article, in:
    Farnell, D., 2013, 'How belief works', Think, volume 12, issue 35, pages 39-60.
  2. Wikipedia: Baruch Spinoza
  3. 3.0 3.1 Gilbert, D., 1991, 'How Mental Systems Believe', American Psychologist, volume 46, number 2, pages 107-119.


7 See also


This article is part of the 'core reading' series of articles:

The certainty of belief > Why belief can't be the product of an assessment of truth > The theoretical argument for credulism > Objections to credulism > The evidence for credulism