To clarify, I mean without deception. In other words, if something seems plausible to me, and I decide to act on it as though it were true while recognizing that I could be mistaken, do I believe it?

And what if the probabilities are flipped? What if I choose to behave as though a remote possibility is true while recognizing that it almost certainly isn't? Do I believe it?

I recently came across the following statement in a published scholarly journal: "Note that accepting a hypothesis does not mean that you believe in it, but only that you act as if it were true." Isn't this contradicted by the principle implied by the phrase "why don't you put your money where your mouth is?" What gives?

  • 3
    Sure. People commonly behave as if they believe when they must act and no better alternative is available, "what do you have to lose, might as well go for it" as they say. For example, relatives may not believe that a new drug or "nontraditional medicine" would help a terminal patient, but they would go for it. The same with accepting a hypothesis or sticking to a dubious theory when nothing else is on offer. Scientific paradigms shift not when old ones falter, but when new ones emerge. Putting money where mouth is when nothing good can come out of it anyway is throwing good money after bad.
    – Conifold
    Commented Sep 14, 2023 at 8:38
  • 1
    I want to add that since your source is a scholarly journal, it's perfectly normal during a study to start from the assumption that a theory is true and push it to its limit even if your aim is to prove that it is false.
    – Jemox
    Commented Sep 14, 2023 at 9:01
  • And what if the probabilities are flipped? What if I choose to behave as though a remote possibility is true while recognizing that it almost certainly isn't? Do I believe it? Do you believe what? That the possibility is true? No. That behaving as if it is true? Yes. It all depends on how you phrase the questioned belief.
    – Tvde1
    Commented Sep 15, 2023 at 11:21
  • 2
    It's not a complete answer, but somehow nobody has mentioned aliefs.
    – Corbin
    Commented Sep 15, 2023 at 21:18

10 Answers 10


I'd say Pascal's Wager is a counter example. You could rationally follow what you think God's wishes would be without believing in God's existence because of the cost of being wrong.


Is there a difference between believing something and behaving as if it were true?

Yes, and the distinction is recognized in epistemic terminology.

Truth that is actually or really true is generally understood by the correspondence theory of truth. That is, when someone says that electrons are real, measures the diameter of the electron, and says, 'The diameter of an electron is X', they are making a claim about reality. This way thinking about the world is called scientific realism. These ideas were big with philosophers like Russell and early Wittgenstein. From WP:

In metaphysics and philosophy of language, the correspondence theory of truth states that the truth or falsity of a statement is determined only by how it relates to the world and whether it accurately describes (i.e., corresponds with) that world... Correspondence theories claim that true beliefs and true statements correspond to the actual state of affairs. This type of theory attempts to posit a relationship between thoughts or statements on one hand, and things or facts on the other.

But other thinkers like Pierce believe that truth has a pragmatic aspect that has nothing to do with whether or not something is actually true. Accordingly, it's called the pragmatic theory of truth. Interestingly, this theory of truth is wielded by instrumentalists who take an anti-realist position on science. It's also used by scientific constructivists who emphasize the role of language and culture in determining truth.

A pragmatic theory of truth is a theory of truth within the philosophies of pragmatism and pragmaticism. Pragmatic theories of truth were first posited by Charles Sanders Peirce, William James, and John Dewey. The common features of these theories are a reliance on the pragmatic maxim as a means of clarifying the meanings of difficult concepts such as truth; and an emphasis on the fact that belief, certainty, knowledge, or truth is the result of an inquiry.

For pragmatic truth, we simply behave as if it is true because it gets us what we want. Thus, an instrumentalist interpretation of a scientific theory is not that it represent truths about what is real, but rather the idea and language is a tool that accomplishes practical things as if those ideas and language were true.

So, if you're new to philosophy, the take away from this question should be the larger question: what is truth and what are the theories about it? It also foreshadows the philosophical topic about the historical debate between realists and nominalists more broadly.

  • 1
    @candied_orange I would argue that Occam's Razor as a heuristic must accommodate for the fact that parsimony is not merely the simplest, but the simplest that produces the most adequacy. Thus additional complexity makes sense in the light of better prediction, explanation, etc. between the theory and its object. For instance, it is not 'Is correspondent truth or coherent truth simpler?' but 'Is a hybrid of correspondent and coherent theory more parsimonious in light of its explanatory power compared to either theory with respective ad-hoc modifications.
    – J D
    Commented Sep 14, 2023 at 15:37
  • Pragmatism may in fact just simply be a recognition that our very foundations of perception and conception are always theory laden, and so far as we are more interested in having our perception and conceptions resolve to teleological aims, the accuracy of our percepts and concepts are subsidiary to the drive to achieve the goal, however formulated.
    – J D
    Commented Sep 14, 2023 at 15:39
  • I don't see what the question has to do with epistemology or scientific realism. The context assumes a correspondence theory of truth and explicitly factors out notions of knowledge or justification. I'm not concerned with convincing myself that I know something or that my beliefs are true, just with whether or not it is proper to call them "beliefs". Commented Sep 14, 2023 at 18:16
  • I believe you, so let's expand. First, 'belief' is a core ontological primitive of epistemology. 'Knowledge' is a function of 'belief' historically as justified, true belief. So there is no epistemology without 'belief' or 'truth' which also a core concept in epistemology and has its intuitive sense located most closely to its use in direct realism and classical empiricism...
    – J D
    Commented Sep 14, 2023 at 18:24
  • I raise 'scientific realism and instrumentalism' because your language directly summarizes the issue in your quotation: "Note that accepting a hypothesis does not mean that you believe in it, but only that you act as if it were true." This statement is antithetical to realism and endorses realism. If you're not familiar with the broader outlines of the positions of scientific realism and instrumentalism (and you don't appear to be), then it will be an impediment to understanding "Putting your money where your mouth is" because...
    – J D
    Commented Sep 14, 2023 at 18:26

Buying a lottery ticket does not imply that you believe that you will win (i.e. that you believe you have the ability to predict randomly selected numbers). There's no reason to equate the behavior of buying a ticket with the belief that you will win, it merely represents the belief that you might win.

  • 1
    As you say, "buying a lottery ticket does not imply that you believe that you will win..." but a genuine counterexample necessarily would imply that. This answer highlights the fact that behaving as though you believe you will win the lottery would involve more than buying a lottery ticket (e.g., quitting your job, shopping for mansions, making travel plans, etc.). Commented Sep 15, 2023 at 20:16

if something seems plausible to me, and I decide to act on it as though it were true while recognizing that I could be mistaken, do I believe it?

I would rather say that you expect it; it's weaker than belief.

what if the probabilities are flipped? What if I choose to behave as though a remote possibility is true while recognizing that it almost certainly isn't? Do I believe it?

Then I'd say you hope for it, against all odds. Or perhaps you fear it enough to take precautions, in spite of the low risk. But you still don't believe.

  • I agree that those would be better words to describe the situations in question, but I was wondering about a technicality. I think that "taking precautions" would generally be weaker than behaving as though a particular outcome is certain (in which case you certainly wouldn't anticipate other possibilities). Commented Sep 15, 2023 at 20:22
  • @StevenHarder English is full of resources, flexible and almost infinitely nuanced. A great language to do philosophy in, because of that. Unfortunately, the analytic tradition seems oblivious of it, and of the power of poetry and literature, more generally.
    – Olivier5
    Commented Sep 16, 2023 at 6:52

This is the distinction in English between belief and trust.

I truly believe flying is safer than driving, having seen the hard data, yet I don't trust that and drive long distances instead out of fear.

If my son says, "Please let me help make the Christmas cookies; I promise I won't eat any this time," but every year he has said that and eaten some anyway, I trust him and let him help, even though I don't believe him and expect he'll probably repeat his usual behavior.

So, belief is cognitive and trust is the choice of action we make.

  • I doubt there is a significant distinction between belief and trust in this context, but you touched on the answer: a strong desire such as fear can drive a person to behave as though the thing they desire (or desire to avoid) is real/obtainable, whether or not they believe it is. Commented Sep 15, 2023 at 19:55

OCD people are obsessed with e.g. washing their hands. I believe (could be wrong) that they don't believe their hands are dirty, and that this isn't necessary for their health, but they do it anyway.

Most people with OCD are well aware that their obsessions and compulsions are irrational.

You might suppose this only applies for mentally ill people.

  • 4
    Practically all people act irrationally in some circumstances (read about behavioral economics, e.g. Ariely's "Predictably Irrational"), so to some extent we're all mentally ill.
    – Barmar
    Commented Sep 14, 2023 at 14:25
  • 1
    I have OCD, and it’s a weird experience. I can verbally tell myself my hands are clean, but strongly feel they are still dirty. I guess your example would apply to those that are under treatment (know they’re clean) but suffer a relapse (merely to feel relief).
    – Hokon
    Commented Sep 14, 2023 at 19:16
  • 1
    i'm similar with psychotic recovery stuff (my psychosis proper had a strong obsessional element): i know that these things are not plausible at all, but i feel they are in fact happening... @Hokon
    – user67675
    Commented Sep 14, 2023 at 19:18

If I don’t believe X without doubt that something is true, then there are two ways how I can go wrong: I act as if X were true when it isn’t, or I act as if X were false when it isn’t. I can then make a rational decision what is more likely and what has the worse outcome if I am wrong.

And sometimes people believe something is true and still act as if it isn’t. I am about 99.999999% sure that I will die soonish and act as if I wouldn’t. Someone might have convincing evidence that their spouse is cheating and act as if it never happened. In a harmless situation I might know I need to go to hospital in four weeks time and go on holiday without telling anyone.


Another attempt by exemplification.

Behavior and belief are linked, but distinct because in the typical case we behave as if we believe, a distinction Ryle recognized as knowledge-how and knowledge-that.

Example: If you act and put out a fire (behavior), it is reasonable to conclude 'you believe there is a fire' and 'your actions will extinguish the fire'.

But, what if someone tells you there is an invisible fire and asks you to douse it, and you behave in the same way you would a visible fire? What do your actions say about your belief?

Scenario One: Let's say that you receive the instructions from a firefighter during a crisis, and that even if you do not observe a fire and don't know that some substances combust with near imperceptible visible emissions, you behave as if there was a fire. Do you believe in the fire? In this case, you simply neither believe nor disbelief there is a fire. You believe that there might be a fire because you believe that your belief of the fire (second-order propositional attitude) is not as important as ensuring that a possible invisible fire is extinguished. Here, the belief about the fire is uncertain and correspondent. What counts is whether or not someone gets burned, not whether or not there is actually a fire.

Scenario Two: Let's say that you receive the instructions from your child engaged in play as a firefighter during bonding time, and that you know there is no fire because the invisibility is a function of the use of imagination. Do you believe in the fire? No. You believe there is no fire, but you believe that your disbelief in the fire is not as important as ensuring that a your child has fun pretending. Here, the belief about the fire is certain and correspondent.

Scenario Three: Let's say that you receive the instructions from a date with romantic and sexual consequences in the balance, and though the claimed fire is invisible, you simply don't know if your date is delusional, if it's actual invisible fire on the habachi grill, or she's having a bit of fun at your expense as you douse the chef, the grill, and other patrons with water. But ultimately, you don't care which is the case. The status of the fire is now one of pragmatic truth. What is important is your belief about beliefs of the fire is irrelevant, in which case you have no belief at all, but just a strong desire for a second date.

So, now, we can answer your question. Does your behavior constitute belief in the invisible fire? In two cases, yes, and one case no. Therefore, to answer your question, not necessarily and as a function of the context.

  • 1
    Those are excellent counterexamples. Thank you. I've learned a lot from both of your answers, and the detailed comments, but the selected answer is what really made the lightbulb go on. Commented Sep 15, 2023 at 20:00

"Note that accepting a hypothesis does not mean that you believe in it, but only that you act as if it were true."

This sounds like someone is collecting evidence. If evidence counters the hypothesis, sounds like they would stop acting like it were true. If evidence supports it, it's no longer a hypothesis, it's a theory (something that explain evidence).

People use the same term for belief for things they know are true, vs things they want to believe are true. Someday, maybe someday neuroscience will be able to detect when people are being honest about if they see a rock about to fall on them and their reflexes want to kick in but they claim to believe that a supernatural being will stop it.


A distinction between belief and action is made explicit in decision theory, particularly in Bayesian decision theory (the version I'll briefly outline here). An earlier answer, referring to Pascal's wager, can be viewed as an example of the application of decision theory as a normative theory for how to choose to act in the midst of uncertainty. Indeed, Wikipedia's page on Decision theory notes that Pascal knew the key ideas of decision theory and invoked them in his eponymous wager argument.

Basically, decision theory says that how one acts should depend, not just on what one believes (and how strongly), but also on judgments about the consequences of one's actions.

(Apologies for the "bare" math notation below; it works in other StackExchange forums.)

To be especially clear, belief in (Bayesian) decision theory is distinct from feeling certain that something is true (which may be what the OP intended). There are degrees of belief, quantified via probability on a 0 to 1 scale (or equivalently with other related scales, such as percentages or odds). For a proposition (hypothesis) $H$, a probability of 0 corresponds to being certain that $H$ is false, a probability of 1 corresponds to being certain that $H$ is true, and values between these extremes correspond to degrees of belief. Probability is viewed as always contextual (i.e., based on some known or presumed information); $P(H|C)$ is the probability that $H$ is true given that the contextual information $C$ is true, the degree to which $C$ implies $H$, etc..

When faced with a choice between various actions whose consequences depend on things ("states of the world") we are not entirely certain about, decision theory requires a certain structure in order to identify an optimal decision (choice of action). The decider needs to specify the following:

  • The action space (the possible decisions, $a_1, $a_2$, etc.);
  • The state space (possible states the world may be in, $s_1$, $s_2$, etc., that bear on the outcome of the action);
  • Enough information to assign probabilities to the states;
  • A utility function, $U(a_i, s_j)$, a function of action and state that specifies the value or reward to the decider if they choose action $a_i$ when the true state is $s_j$. Equivalently (pessimistically rather than optimistically!) the decider may specify a loss function, $L(a_i, s_j)$, that specifies the cost to the decider if action $a_i$ is chosen when the true state is $s_j$.

In discrete settings (as here), the utility or loss function may be represented as a matrix.

One simple class of decision problems has as actions simply asserting that one of the possible states is in fact the true state. This class of problems arises commonly in statistics, as briefly described below. It speaks particularly clearly to the question of distinguishing action from belief.

Decision theory starts from some basic, appealing desiderata and shows that the optimal decision (choice of action among the $a_i$) is the one with the greatest expected utilitity, computed for each possible action by adding up all the utility values for that action and every possible state, weighted by the probability for each state. Equivalently, one should choose the action with the lowest expected loss.

It should be easy to see that decision theory does not in general lead one to act as if the state with the largest probability were the true state. A simple but clear example is the game of Russian roulette: You are offered some winnings, say, $1,000, to point a revolver at your head and pull the trigger, knowing that only one of its six chambers have a bullet, and after the cylinder has been spun so that the probability that the bullet is in the active chamber is $1/6$. It is five times more probable that the active chamber is empty. That is, one's belief is strong that pulling the trigger is safe. Nevertheless, one's sanity would be legitimately questioned if one agreed to play the game. It is much more likely that the active chamber is empty rather than full. But the consequences are much worse if the chamber is full and one plays (you get the winnings but lose your life), versus if the chamber is empty but one chooses not to play (you do not gain the winnings, but you keep your life).

This is what I was getting at above when I wrote that decision theory says that how one acts should depend, not just on what one believes (and how strongly), but also on judgments about the consequences of one's actions.

It's worth noting that it can be hard to specify utility or loss functions. For the Russian roulette example, in order to formulate it as a decision theory problem, you'd need to assign a dollar value to your life (though it's possible to reach a decision just by bounding that dollar value).

Decision theory is commonly used in statistics to identify the best estimate of some real-valued parameter (say, the amount of rainfall tomorrow) when the available data (and any other knowledge or assumptions) cause one to be uncertain about the parameter's value. The uncertainty can be represented by a probability density function (a so-called posterior probability density in Bayesian statistics) over the possible values of the parameter. If the utility function grants you a reward for correctly estimating the parameter's value, but nothing if you are incorrect, the best estimate the one with the largest probability density (the mode, e.g., the amount of rain for which the probability density is largest). But if there is some cost to being incorrect that depends on the size of the error you make, in general the best estimate won't be the one with the largest probability density. For example, if the loss function is quadratic with distance from the true value, then it turns out the best estimate is the posterior mean—a probability-weighted average of the possible values. When the uncertainty is symmetric about the mode, the posterior mean is equal to the mode. But in general the posterior mean is different from the mode. That is, in statistics, we quite commonly "act" (choose a parameter estimate) in a way that doesn't exactly mirror our "belief" (where the largest probability is).

  • As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
    – Community Bot
    Commented Sep 19, 2023 at 7:10

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .