Foundationalist

Foundationalism is a theory in epistemology about the structure of justification and knowledge. It holds that beliefs are justified either non-inferentially as foundations or inferentially through their relation to those foundations. In classical foundationalism, some beliefs are basic: they do not require justification from other beliefs, and they provide the secure base for justifying non-basic, or derivative, beliefs. Basic beliefs are often conceived as self-evident, incorrigible, or immediately evident in experience.

There are various formulations of foundationalism. Modest or contemporary versions typically allow properly basic beliefs—those rationally accepted because they reliably track reality, not merely because they are self-evident. Externalist readings tie justification to the reliability of cognitive processes or experience, while internalist readings require that the justification be accessible to an agent's mental states.

Foundationalism is often contrasted with coherentism, which denies a separate foundational layer and instead constructs justification through the coherence of a belief system; and with infinitism, which allows an endless chain of justification. Key debates concern the nature and identification of basic beliefs, how they ground other beliefs, and whether such foundations can be secure or legitimate given issues like perception, memory, and epistemic regress.

Historically associated with early modern rationalism and figures such as Descartes, foundationalism has been developed and revised by later philosophers, including proponents of properly basic beliefs. It remains a central position in discussions about the architecture of justification and the nature of knowledge.