Coherentism is a theory of epistemic justification. It implies that for a belief to be justified it must belong to a coherent system of beliefs. For a system of beliefs to be coherent, the beliefs that make up that system must “cohere” with one another. Typically, this coherence is taken to involve three components: logical consistency, explanatory relations, and various inductive (non-explanatory) relations. Rival versions of coherentism spell out these relations in different ways. They also differ on the exact role of coherence in justifying beliefs: in some versions, coherence is necessary and sufficient for justification, but in others it is only necessary.
Coherentism, as mentioned above, is usually contrasted with the theory of epistemic justification known as foundationalism:
Foundationalism is any theory in epistemology (typically, theories of justification, but also of knowledge) that holds that beliefs are justified (known, etc.) based on what are called basic beliefs (also commonly called foundational beliefs). Basic beliefs are beliefs that give justificatory support to other beliefs, and more derivative beliefs are based on those more basic beliefs. The basic beliefs are said to be self-justifying or self-evident, that is, they enjoy a non-inferential warrant (or justification), i.e., they are not justified by other beliefs. Typically and historically, foundationalists have held either that basic beliefs are justified by mental events or states, such as experiences, that do not constitute beliefs (these are called nondoxastic mental states), or that they simply are not the type of thing that can be (or needs to be) justified.
Hence, generally, a Foundationalist might offer the following theory of justification:
- A belief is epistemically justified if and only if (1) it is justified by a basic belief or beliefs, or (2) it is justified by a chain of beliefs that is supported by a basic belief or beliefs, and on which all the others are ultimately based.
A basic belief, on the other hand, does not require justification because it is a different kind of belief than a non-foundational one.