Externalism

Externalism is a family of philosophical theories that hold that factors outside a subject’s own mind can partly determine or constitute certain mental states, meanings, or epistemic status. It stands in contrast to internalist views that locate these aspects wholly within the individual’s private mental life. The term covers several related but distinct strands, including semantic externalism about meaning and content and epistemic externalism about justification and knowledge.

In the philosophy of language and mind, semantic externalism argues that the content of our thoughts and the meaning of our terms depend in part on external conditions. Hilary Putnam’s Twin Earth scenario is a classic formulation: terms like “water” refer to the substance's actual natural kind in the environment, not merely to what the term evokes internally. Saul Kripke and Hilary Putnam influenced further work, while Paul Burge argued that mental content can depend on factors in the speaker’s linguistic community. In general, externalism posits that environment, social institutions, and natural kind facts contribute to what our mental states represent.

Epistemic externalism, another major strand, holds that justification or entitlement to knowledge can rely on factors outside the subject’s internal states, such as reliable cognitive processes (reliabilism) or external safeguards against error. This view raises questions about internal access, epistemic luck, and the boundaries of knowledge.

Externalism has generated substantial debate, attracting criticisms from internalists who emphasize mental accessibility and from skeptics who worry about meaning, content, and justification being too dependent on external factors. Notable figures include Putnam, Burge, and Goldman.