Semantic Externalism

Overview and Core Thesis

Semantic externalism is a position in the philosophy of language and mind which holds that the meaning (or content) of words and thoughts is determined not only by what is “in the head” of an individual speaker or thinker, but also by factors external to that individual. These factors can include the natural environment, the social–linguistic community, and historical–causal relations between speakers and objects.

In contrast, semantic internalism (or individualism) maintains that once all the internal physical and psychological facts about a person are fixed, the meanings of their words and the contents of their thoughts are also fixed. Externalists deny this: they claim that two individuals could be internally identical yet mean different things by the same word or entertain different thoughts, because they inhabit different environments or linguistic communities.

Semantic externalism became a major topic in late 20th‑century analytic philosophy, especially through the work of Hilary Putnam and Tyler Burge, and continues to shape debates about reference, mental content, self-knowledge, and the nature of intentionality.

Classical Arguments for Semantic Externalism

Putnam’s Twin Earth

Hilary Putnam’s famous Twin Earth thought experiment (1970s) is a central argument for externalism about natural kind terms. Imagine a planet, Twin Earth, that is physically just like Earth in every respect except one: the liquid that fills lakes and oceans is not H₂O but a different microphysical substance, XYZ, which is indistinguishable at the everyday level. Twin Earth inhabitants call this liquid “water,” just as we do.

In 1750, before the chemistry of water was known, an Earthling and their molecule‑for‑molecule doppelgänger on Twin Earth would be psychologically identical. Yet, Putnam argues, when each says “water,” they refer to different substances: H₂O on Earth, XYZ on Twin Earth. This suggests that reference and meaning depend partly on the external chemical structure of the stuff one is causally related to, not just on one’s internal mental state. Hence Putnam’s slogan: “Meanings just ain’t in the head.”

Burge’s Arthritis Case

Tyler Burge extended externalism from language to mental content and from natural kinds to ordinary social concepts. In his well‑known arthritis example, a patient falsely believes that he has “arthritis” in his thigh. According to the medical and ordinary meaning in his community, arthritis is a disease of the joints, so his belief is partly about that communal concept.

Burge considers a counterfactual situation in which there is a slightly different linguistic community, where “arthritis” is stipulatively used for a wider class of ailments including non‑joint inflammations. A subject in that community, internally identical to the original patient, would have a different belief when thinking “I have arthritis in my thigh,” because the public meaning of “arthritis” in that community is different.

Burge concludes that the content of the belief itself—not just the public word—depends on the social environment. Even if two people are internally indistinguishable, what they believe can differ because the communal norms that fix their concepts and terms differ.

Causal–Historical Theories of Reference

Both Putnam and other externalists (e.g., Saul Kripke) emphasize causal–historical chains as determinants of meaning. On such views, a term like “gold” refers to whatever substance stands at the causal origin of the term’s use—paradigmatic samples that speakers continue to track and refer back to, even if their internal descriptions are partly mistaken or incomplete.

This undermines purely descriptivist or internalist theories of meaning, which tie reference entirely to mental descriptions possessed by each speaker, and supports the idea that meaning is partly anchored in external causal relations and community practices.

Varieties and Applications

Externalism about Linguistic Meaning vs. Mental Content

A useful distinction is between:

• Semantic externalism (language): The meanings of words and sentences depend partly on environmental or social factors.
• Content externalism (mind): The propositional contents of beliefs, desires, and other mental states depend partly on such factors.

Some philosophers accept externalism for natural kind terms while remaining internalists about many mental states; others, following Burge, adopt a broad content view, where many beliefs and thoughts are externally individuated.

Natural Kind vs. Social Externalism

Contemporary discussions often distinguish:

• Natural kind externalism: Meaning depends on the natural environment, such as chemical structure (water/H₂O) or biological species (tiger, elm).
• Social externalism: Meaning and thought content depend on social norms, linguistic practices, and expert communities, as in technical terms (arthritis, electron) whose full content is partly fixed by specialists.

In practice, many externalist theories combine both: the reference of “electron,” for instance, depends on both underlying physical reality and the theoretical commitments of physicists.

Externalism in Philosophy of Mind and Cognitive Science

Externalism has important implications beyond language:

• Individuation of mental states: If beliefs are externally individuated, then two internally identical individuals might be in different mental states, raising questions about the explanatory role of psychology and neuroscience.
• Wide vs. narrow content: Some theorists distinguish “wide” (externally dependent) from “narrow” (purely internal, functionally individuated) content to reconcile externalist semantics with internalist scientific explanation.
• Extended mind debates: Although distinct, externalism about content has influenced arguments that cognitive processes themselves can extend beyond the brain to tools and environments (e.g., notebooks, digital devices).

Debates and Criticisms

Internalist Objections

Critics of semantic externalism raise several concerns:

• Psychological explanation: If mental states are partly determined by external factors, how can psychology and cognitive science explain behavior by focusing on the individual’s internal states alone? Internalists argue that scientific explanation requires contents that “supervene” on internal structure.
• Epistemic access: If what one thinks depends on external factors one might not fully know (e.g., expert theories of arthritis), then it seems possible to be mistaken about one’s own thoughts, apparently challenging the idea of privileged self-knowledge.
• Fregean sense and mode of presentation: Some maintain that externalist accounts neglect the cognitive significance of expressions, focusing on reference at the expense of the internally accessible “sense” or way in which an object is thought of.

Self-Knowledge and Compatibility Debates

One prominent line of discussion concerns whether externalism is compatible with immediate self-knowledge. Proponents of externalism often propose that:

• Self-knowledge concerns a subject’s occurrent mental states, access to which can be authoritative even if the precise environmental determinants of their content are not fully known.
• Or they distinguish between knowing that one is thinking a certain content and knowing all the external facts that help fix that content.

Internalists and some epistemologists remain skeptical, arguing that if content varies with hidden environmental facts, then first-person access cannot be as secure as traditionally assumed.

Pragmatic and Meta-Semantic Alternatives

Some philosophers accept externalist intuitions about Twin Earth and Burge-style cases but interpret them differently. For example:

• Two-dimensional semantics attempts to capture both internal and external aspects of meaning, assigning expressions a primary (epistemic or cognitive) and a secondary (world‑relative) intension.
• Pragmatic or inferentialist approaches suggest that much of what externalists attribute to external content may be better treated in terms of use, norms of assertion, or patterns of inference, rather than as metaphysically robust external determinants of meaning.

Despite such alternatives, semantic externalism remains a central and widely discussed viewpoint, forming a key contrast class for theories of meaning and mental content in contemporary analytic philosophy.