There is more to knowledge than just true belief. One can gain a true belief by sheer luck whereas knowledge has to be the result of one’s efforts. Identifying true belief with knowledge is implausable. But what’s the missing ingredient? The classical account of knowledge requires justification of one’s belief as an additional component. Justification means that someone has good reasons for thinking that what one believes is true. (Pritchard, p. 23)
Examples for good reasons in favour of one’s belief: having seen something with one’s own eyes, having been told by a reputable expert in a particular field, having read something in an authoritative book, having followed an established procedure to arrive at a certain belief, etc.
Prejudice, superstition and astrology are not typically seen as epistemically appropriate ways of forming one’s belief. One cannot convincingly justify a belief on that basis.
There are two types of justification (Ichikawa, Steup):
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Propositional justification: a subject has sufficient reason to believe a given proposition.
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Doxastic justification: a given belief is held appropriately.
The classical account – often called the tripartite account of knowledge as it consists of three parts – states that Truth, Belief and Justification are each necessary conditions for knowledge. In combination, as justified true belief, they are thought to be a sufficient condition for knowledge.