The primary problem in epistemology is to understand exactly what is needed in order for us to have true knowledge.
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 sincere believer in the flat earth theory does not know that the Earth is flat. Later epistemologists, for instance Gettier (1963) and Goldman (1967), have questioned the "justified true belief" definition. Belief as a psychological theory
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.
While some have argued that beliefs are represented in the mind as sentence-like constructs, others have gone as far as arguing that there is no consistent or coherent mental representation that underlies our common use of the belief concept and that it is therefore obsolete and should be rejected.
Our common-sense understanding of belief is correct - Sometimes called the "mental sentence theory," in this conception, beliefs exist as coherent entities, and the way we talk about them in everyday life is a valid basis for scientific endeavour. Jerry Fodor is one of the principal defenders of this point of view.
Our common-sense understanding of belief may not be entirely correct, but it is close enough to make some useful predictions -
This view argues that we will eventually reject the idea of belief as we use it now, but that there may be a correlation between what we take to be a belief when someone says "I believe that snow is white" and how a future theory of psychology will explain this behaviour.
Our common-sense understanding of belief is entirely wrong and will be completely superseded by a radically different theory that will have no use for the concept of belief as we know it -
Known as eliminativism, this view, (most notably proposed by Paul and Patricia Churchland), argues that the concept of belief is like obsolete theories of times past such as the four humours theory of medicine, or the phlogiston theory of combustion.
The Churchlands argue that our common-sense concept of belief is similar in that as we discover more about neuroscience and the brain, the inevitable conclusion will be to reject the belief hypothesis in its entirety.
Our common-sense understanding of belief is entirely wrong; however, treating people, animals, and even computers as if they had beliefs is often a successful strategy -
The major proponents of this view, Daniel Dennett and Lynne Rudder Baker, are both eliminativists in that they hold that beliefs are not a scientifically valid concept, but they don't go as far as rejecting the concept of belief as a predictive device.
While few people would agree that the computer held beliefs, treating the computer as if it did (e.g. that the computer believes that taking the opposition's queen will give it a considerable advantage) is likely to be a successful and predictive strategy.
In this understanding of belief, named by Dennett the intentional stance, belief-based explanations of mind and behaviour are at a different level of explanation and are not reducible to those based on fundamental neuroscience, although both may be explanatory at their own level.
How beliefs are formed
People may adopt the beliefs of a charismatic leader, even if those beliefs fly in the face of all previous beliefs, and produce actions that are clearly not in their own self-interest.
Is belief voluntary?
Rational individuals need to reconcile their direct reality with any said belief; therefore, if belief is not present or possible, it reflects the fact that contradictions were necessarily overcome using cognitive dissonance.
Advertising can form or change beliefs through repetition, shock, and association with images of sex, love, beauty, and other strong positive emotions. Physical trauma, especially to the head, can radically alter a person's beliefs.
Commendatory - an expression of confidence in a person or entity, as in, "I believe in his ability to do the job." Existential claim - to claim belief in the existence of an entity or phenomenon with the implied need to justify its claim to existence.
Psychiatrist and historian G.E. Berrios has challenged the view that delusions are genuine beliefs and instead labels them as "empty speech acts," where affected persons are motivated to express false or bizarre belief statements due to an underlying psychological disturbance.
In Lewis Carroll's Through the Looking-Glass the White Queen says, "Why, sometimes I've believed as many as six impossible things before breakfast." This is often quoted in mockery of the common ability of people to entertain beliefs contrary to fact.