A coherence theory bases the
truth of a
belief on the degree to which it coheres ("hangs together") with all the other beliefs in a system of beliefs (typically one person's beliefs, but it could be any body of knowledge).
In philosophies of idealism, all the ideas or beliefs are said to cohere with one another, perhaps because the world is reason itself or created by a rational agent.
In scientific theories, every new observational fact must be integrated with existing facts to make them maximally coherent. Perfect coherence is not to be expected, of course.
Charles Sanders Peirce's theory of pragmatic truth is the coherent inter-subjective agreement of an open community of inquirers.
In analytic language philosophy, the truth of a proposition depends on its agreement with some larger set of propositions, ideally all known true propositions and any logical inferences from those propositions.
In traditional epistemology, the coherence may be internal to a personal set of beliefs that are accessible to a subject. In this case, coherence is one way to
justify a belief.
The coherence theory is close to the
consistency theory of truth. But consistency is only possible for relatively modest logical and mathematical systems. In a system of belief as large as the culture of a society, there are many conflicting beliefs. Even in the mind of a single subject, consistency of beliefs is more demanding than coherence, but neither is very likely.
Coherence and consistency are best understood as desirable conditions for any theory of
truth, including the
correspondence theory of truth.
