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

At a basic level, we all know what belief is. That is, at a basic level, we all know what it means to believe something, from the profound – such as the belief that humans are apes – to the mundane – such as the belief that David is vegetarian. Indeed, the concept of belief is one of the most fundamental of human psychology. However, this concept is one of those everyday concepts that we all understand at a basic level but which are surprisingly difficult to define, like art or happiness.

Believing something versus something believed

The psychological state of belief involves a claim. In the above examples it's believed that humans are apes and that David is vegetarian.

Indeed, the term belief can refer to either the psychological state or simply the believed claim. That is, it can refer to either believing something or something believed. For example, in the first sense my belief that humans are apes is distinct from someone else's belief that humans are apes, in the sense that they’re separate psychological states existing in different heads. But in the second sense they’re the same belief: Humans are apes.

So the term profound belief can refer to either belief of a profound claim or a profound claim that's believed – and likewise for the term mundane belief, and for the terms true belief and false belief.

This article is concerned with the definition of belief in the sense of the psychological state, the primary sense of this term.

In the secondary sense, the term belief is often used by itself to specifically mean a believed claim that’s either a moral, political, religious, philosophical or scientific claim, as when we refer to our ‘beliefs’. But the subject of How Belief Works is our belief of any kind of claim, however profound or mundane. Other examples of mundane beliefs are my current beliefs that I’m in my flat, I'm sitting on a chair at my desk, I'm typing these words, it's Tuesday morning, it’s sunny outside, and I went for a hike along a river yesterday.

Six ways to misdefine belief

The first edition of the best-selling university-level psychology textbook Psychology provides a definition of belief that actually makes three false claims about belief – and despite being only ten words long. It also commits an error of omission. One of the co-authors is Daniel Gilbert, a Harvard psychology professor who has researched belief. The other three authors – Daniel Schacter, Daniel Wegner and Bruce Hood – are also Harvard psychology professors.

They defined belief as:

An enduring piece of knowledge about an object or event.

First, beliefs aren’t necessarily 'enduring'.

A belief can be replaced by a contrary belief any length of time, however short, after its formation. And given the speediness of the brain, which functions on the timescale of milliseconds, that can be less than a second. For example, if we conclude that Kate is lying we may cease holding this belief the next moment upon remembering something which implies that what Kate is saying is actually true.

It could be argued that our core beliefs must by definition be at least somewhat enduring. And perhaps the authors had this particular type of belief in mind. But they’re offering an unqualified definition of 'belief', and beliefs aren't necessarily enduring.

Second, although a 'piece of knowledge' is a belief, a belief isn’t necessarily a piece of knowledge.

A false belief obviously isn’t knowledge, given that knowledge is by definition true.

And even a true belief isn’t necessarily knowledge. For example, if someone believes that their lottery ticket will win the jackpot, and it then does, then their belief was true. But, if it was a fair draw, it couldn't be correctly said that they knew they'd win, given that the outcome of the random draw was, by definition, unknowable in advance. It could merely be correctly said that they believed they'd win, and happened to be right. Indeed, knowledge is commonly defined in philosophy as ‘justified true belief’ – that is, belief that’s true, and true not by chance but because the believer has a logical justification for the belief.

Third, beliefs aren’t necessarily about an 'object or event'.

Beliefs can also be about concepts – including ideas, theories, rules, norms and conventions. Concepts can concern objects – including people – and events – including actions. And they’re stored via physical objects, such as paper, computer memory or brains. And their involvement in our thinking, or appearance on a screen, is an event. But they aren't themselves objects or events, being instead abstract. In the case of concepts concerning pure mathematics and logic, they don’t ever even concern objects or events.

The fourth error concerns not something that the definition states, but something that it fails to state.

It refers to a ‘piece of knowledge’, which is knowledge in the sense of something known, as opposed to the psychological state of knowing something. Therefore this definition concerns belief in the sense of a believed claim – something believed – but not in the sense of the psychological state – believing something. And this is despite the latter sense being the primary sense of the term belief, and also despite this definition being in a psychology textbook.

In the second edition of Psychology the definition of belief has been revised. It now only commits one of the above four errors, but it also commits two new ones.

The definition is now:

An assumed knowledge about an object or event that is not proven.

The definition no longer states that beliefs are enduring.

Also, it now states not that belief is knowledge, but merely that it’s assumed to be. The definition presumably means that this assumption is made by the believer, although it should explicitly state this.

Also, given that the definition now refers to just 'knowledge' rather than a 'piece of knowledge', it now can be referring to knowledge in the sense of the psychological state of knowing something. So it can now be a definition of belief in the sense of the psychological state. Although, it also can still be referring to knowledge in the sense of something known. And, either way, the inclusion of the word an at the beginning is ungrammatical.

However, the alleged assumption of the believer that this psychological state constitutes knowledge is actually a belief about their belief. So this assumption actually can't be a defining aspect of belief itself. It isn’t even possible for us to make this assumption about every belief that we hold, given that doing so would require the generation of an infinite series of beliefs about beliefs.

Also, the definition still restricts belief to being about an object or event.

Also, a belief doesn’t necessarily involve a claim that’s 'not proven'. This part of the definition implies that we cease believing an unproven claim upon it being proved, which is nonsensical. Indeed, we often only start believing a claim upon it being proved.

This error is also made by the definition of belief in Pan Books’s A Dictionary of Philosophy, which was edited by philosophy professors Antony Flew and Stephen Priest. It states that belief involves:

… holding a proposition p to be true where there is some degree of evidence, though not conclusive evidence, for the truth of p. Clearly related to knowledge, belief may be characterized as stronger than mere ungrounded opinion but weaker than full knowledge.

But even to have the ungrounded opinion that, for example, Kate is lying is to believe that Kate is lying. And even to know that Kate is lying is to believe that Kate is lying. Indeed, the same dictionary’s entry for knowledge states that there's general agreement within philosophy that knowledge is a particular type of belief.

This error is perhaps due to the terms opinion and knowledge normally being used instead of belief to refer to these extremes of belief, in order to communicate the nature of such beliefs. That is, this might have led Flew and Priest to the false idea that such extremes of belief are different from belief, and that belief is therefore only what exists between them.

In sum, the above revised definition of belief, in this best-selling university-level psychology textbook, written by four Harvard psychology professors, still makes three false claims about belief – although now in twelve words instead of ten. And this version also appears in the third, current, edition.

So these two attempts to define belief together err in six different ways.

One way to avoid misdefining belief

Most best-selling university-level psychology and philosophy textbooks fail to even attempt a definition of belief, despite this concept being one of the most fundamental in psychology and philosophy, and despite providing definitions of equally fundamental concepts.

For example, the blurb for another psychology textbook called Psychology, by psychology professors Peter Gray and David Bjorklund, states that it's a 'rigorous ... introduction to psychology'. But the glossary doesn't have an entry for belief, despite having entries for equally fundamental concepts. And nor is belief defined elsewhere in the book's 750 pages.

Belief is also not defined anywhere in the following textbooks:

• the 992-page, 2.7-kilogram (paperback), Psychology, by psychology writer Richard Gross – the blurb states: 'It is the essential introduction to psychology, covering all students need to know to understand and evaluate classic and contemporary topics'

• the 948-page Cognitive Psychology, by psychology professor Michael Eysenck and cognitive science professor Mark Keane – the blurb states: ‘… [it] provides comprehensive yet accessible coverage of all the key areas in the field ... Each chapter is complete with key definitions ...’

• Philosophy of Mind, by philosophy professor John Heil – the blurb states: ‘… [a] guide for students ... to central issues of philosophy of mind’.

The term belief is at least in the index of the first of the above four textbooks. In the case of the other three, it isn’t even in their indexes, despite equally fundamental concepts being in them.

Even some psychology and philosophy reference books fail to provide a definition of belief, despite providing definitions of equally fundamental concepts. For example, the academic editors of the following books didn’t think that belief warranted even a short entry:

• Oxford University Press’s encyclopedia The Oxford Companion to the Mind, edited by psychology professor Richard Gregory

• Penguin Books's The Penguin Dictionary of Philosophy, edited by philosophy professor Thomas Mautner

• Wiley’s Concise Encyclopedia of Psychology, edited by psychologist Raymond Corsini and economist Alan Auerbach.

And even some books that are specifically about belief fail to define it. For example, the index for The Believing Brain, a book on the psychology of belief by science writer and academic Michael Shermer, indicates that belief is defined on pages 5 to 8, but it isn't – these pages are about how and why beliefs form, and belief isn't even briefly defined here, and nor is it elsewhere.

So what is the correct definition of belief?

Given that belief involves a claim, it might be thought that the correct definition of belief is as obvious as it is simple: considering a claim to be true. However, as I’ll explain in the next article, on how beliefs form, even this definition is wrong.

Next article: How Beliefs Form – Part 1

How Belief Works