Internalism holds that the justification of a belief is determined solely by the internal states of the believer, such as their evidence, reasons, and cognitive processes.

Externalism holds that the justification of a belief depends on factors external to the believer, such as the evidence, the reliability of the sources of information, and the social context in which the belief is held.

Coherentism is an internalist theory of justification that holds that a belief is justified if it is coherent with the believer's other beliefs.

Reliabilism is an externalist theory of justification that holds that a belief is justified if it is formed by a reliable process.

Common objections to internalism include the claims that it is too subjective, too narrow, and too demanding.

Common objections to externalism include the claims that it is too objective, too broad, and too permissive.

Key issues in the debate between internalism and externalism include the role of evidence, social factors, and cognitive processes in justification.

René Descartes is most closely associated with internalism, particularly with the foundationalist theory of justification.

W.V.O. Quine is most closely associated with externalism, particularly with the naturalist theory of justification.

The debate over physicalism, the debate over qualia, and the debate over consciousness are all contemporary debates in the philosophy of mind that are related to the debate between internalism and externalism.

Internalism does not necessarily imply skepticism, the impossibility of knowledge, or the unnecessity of justification.

Externalism does not necessarily imply skepticism, the impossibility of knowledge, or the unnecessity of justification.

Internalism does not necessarily imply the impossibility of moral responsibility, the illusion of free will, or the truth of determinism.

Externalism does not necessarily imply the impossibility of moral responsibility, the illusion of free will, or the truth of determinism.

Internalism does not necessarily imply moral relativism, the falsity of moral objectivism, or the subjectivity of moral values.

Externalism does not necessarily imply moral relativism, the falsity of moral objectivism, or the subjectivity of moral values.