Belief is the psychological state in which an individual holds a proposition or premise to be true.

Belief, knowledge and epistemology

The relationship between belief and knowledge is subtle. Believers in a claim typically say that they know that claim. For instance, those who believe that the Sun is a god will often report that they know that the Sun is a god. However, the terms belief and knowledge are used differently by philosophers. It is a telling point concerning the nature of belief that most people distinguish between what they know and what they believe, even though they consider both kinds of statements to be true.

Epistemology is the philosophical study of knowledge and belief. The primary problem in epistemology is to understand exactly what is needed in order for us to have knowledge. In a notion derived from Plato's dialogue Theaetetus, philosophy has traditionally defined knowledge as justified true belief. The relationship between belief and knowledge is that a belief is knowledge if the belief is true, and if the believer has a justification (reasonable and necessarily plausible assertions/evidence/guidance) for believing it is true.

A false belief is not considered to be knowledge, even if it is sincere. A sincere believer in the flat earth theory does not know that the Earth is flat. Similarly, a truth that nobody believes is not knowledge, because in order to be knowledge, there must be some person who knows it.

Later epistemologistsWho: date=April 2009 have questioned the "justified true belief" definition, and some philosophersWho: date=April 2009 have questioned whether "belief" is a useful notion at all.

Beliefs are the assumptions we make about ourselves, about others in the world and about how we expect things to be.

Beliefs are also how we think things really are.

Belief as a psychological theory

Mainstream psychology and related disciplines have traditionally treated belief as if it were the simplest form of mental representation and therefore one of the building blocks of conscious thought. Philosophers have tended to be more abstract in their analysis and much of the work examining the viability of the belief concept stems from philosophical analysis.

The concept of belief presumes a subject (the believer) and an object of belief (the proposition). So, like other propositional attitudes, belief implies the existence of mental states and intentionality, both of which are hotly debated topics in the philosophy of mind whose foundations and relation to brain states are still controversial.

Beliefs are sometimes divided into core beliefs (those which you may be actively thinking about) and dispositional beliefs (those which you may ascribe to but have never previously thought about). For example, if asked 'do you believe tigers wear pink pajamas ?' a person might answer that they do not, despite the fact they may never have thought about this situation before.