Hilary Putnam

Early Life and Education

Hilary Whitehall Putnam was born on July 31, 1926, in Chicago, Illinois. His father, Samuel Putnam, was a scholar and translator of Romance languages. Putnam studied at the University of Pennsylvania and earned his Ph.D. at UCLA in 1951, studying under Hans Reichenbach, a leading figure of logical empiricism.

Functionalism and Its Repudiation

Putnam's earliest major contribution to the philosophy of mind was functionalism — the thesis that mental states are defined by their functional roles (their causal relations to inputs, outputs, and other mental states) rather than by their physical constitution. In a series of papers in the 1960s, Putnam argued that minds are to brains as software is to hardware: the same mental state can be "multiply realized" in different physical substrates.

Functionalism became the dominant position in the philosophy of mind. However, in a remarkable act of philosophical honesty, Putnam later repudiated his own creation. In Representation and Reality (1988), he argued that functionalism — like all reductive accounts of mental content — fails because meaning and belief are determined partly by the external social and physical environment, not solely by internal functional organization.

Philosophy of Language: Twin Earth and the Causal Theory of Reference

Putnam's most famous thought experiment, introduced in "The Meaning of 'Meaning'" (1975), asks us to imagine a Twin Earth identical to ours except that the liquid in lakes and taps is not H₂O but a different substance, XYZ, with identical superficial properties. Putnam argued that when an Earthling says "water" she refers to H₂O, and when a Twin Earthling says "water" she refers to XYZ, even if the two are psychologically identical. Therefore, "meanings ain't in the head" — reference is determined partly by the environment, not solely by the speaker's mental states.

This externalist semantics, developed in parallel with Kripke's work on rigid designation, established the causal theory of reference and transformed the philosophy of language.

Pragmatic Realism and Internal Realism

Putnam's philosophical trajectory moved from scientific realism to what he called "internal realism" or later "pragmatic realism." In Reason, Truth, and History (1981), he introduced the brain-in-a-vat thought experiment — a modern version of Descartes' evil demon — to argue against metaphysical realism (the "God's eye view" of reality). If we were brains in vats, Putnam argued, our words "brain" and "vat" would not refer to actual brains and vats, because reference requires causal connection. Therefore, we cannot coherently state the skeptical hypothesis.

Putnam defended a middle path between metaphysical realism and relativism: truth is not mere correspondence with mind-independent reality, but neither is it merely what our community agrees on. His "internal realism" held that truth is an idealization of rational acceptability — what would be justified under epistemically ideal conditions.

In his later work, Putnam moved away from internal realism toward a "natural realism" or "common-sense realism" influenced by William James and Ludwig Wittgenstein, arguing that perception is not mediated by internal representations but is a direct openness to the world.

Mathematics, Ethics, and Later Work

Putnam also made important contributions to the philosophy of mathematics (the Quine-Putnam indispensability argument for mathematical realism), the fact-value entanglement (challenging the strict fact/value dichotomy), and Jewish philosophy. The Collapse of the Fact/Value Dichotomy (2002) argued that the sharp distinction between facts and values is untenable — evaluative and descriptive concepts are deeply entangled.

Putnam spent most of his career at Harvard, where he was the Cogan University Professor. He was also politically active, notably in the anti-Vietnam War movement. He died on March 13, 2016, in Arlington, Massachusetts.