Internalism and Externalism

Internalism and externalism in epistemology denote two competing accounts of what makes a belief justified — or, in a related debate, what makes a belief constitute knowledge.

Internalism holds that the factors relevant to a belief's justification are accessible to the believer by reflection: one's reasons, evidence, and the internal states of one's mind. On the internalist picture, two believers with identical internal states are equally justified, regardless of how their beliefs relate to the external world.

Externalism holds that justification depends on facts about the believer's relationship to the world that may not be accessible by introspection. The paradigm case is reliabilism: a belief is justified if it is produced by a reliable cognitive process, whether or not the believer knows that the process is reliable.

The debate crystallized around skeptical scenarios: a brain in a vat and a normally embedded human, internally identical, are equally justified by internalist lights but differently justified (the brain in a vat relies on unreliable processes) by externalist lights. Internalists take this as an objection to externalism — surely both believers are doing equally well. Externalists take it as an objection to internalism — if justification cannot distinguish the two, it has lost contact with truth-tracking, which is the point of justification.