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Hilary Putnam (1926–2016)

Putnam was a philosopher who spent his career working between two positions he considered untenable: metaphysical realism (there is one true description of the world, and we can converge on it) and relativism (any description is as good as any other). His central contribution is the articulation of a middle ground — internal realism, later reworked as pragmatic realism — that maintains that the world constrains what we can say about it, while denying that there is a single privileged description. The position requires a concept he called conceptual relativity: different conceptual schemes can give equally valid descriptions of the same reality without either being reducible to the other. Putnam was also one of the most influential philosophers of mind and language of the twentieth century — his twin-earth thought experiment, his functionalism (and later rejection of it), and his arguments against skepticism reshaped multiple fields. The trajectory of his career — from scientific realism through internal realism to a pragmatic realism indebted to James and Dewey — is itself a philosophical argument about how much realism can survive honest reflection.

Life

Born 31 July 1926 in Chicago, Illinois. His father Samuel Putnam was a translator, columnist, and writer; his mother Riva was a translator. The household was left-wing and intellectual. Undergraduate at the University of Pennsylvania (BA in mathematics and philosophy, 1948). PhD at the University of California, Los Angeles (1951), under Hans Reichenbach — the logical empiricist whose work on probability and the direction of time shaped Putnam’s early commitment to scientific realism and his lifelong engagement with the philosophy of science.

Taught at Northwestern University (1951–52), Princeton (1953–61), and MIT (1961–65). Appointed professor of philosophy at Harvard (1965), where he spent the remainder of his career. Cogan University Professor of the Humanities (1976–2000) — a university-wide chair reflecting the breadth of his work across philosophy of mind, philosophy of language, philosophy of science, mathematics, and ethics.

Politically active in the late 1960s: supported the Progressive Labor Party, a Maoist-aligned organisation, and co-taught courses with radical students. He later distanced himself from the PLP, describing the involvement as a mistake, though not the underlying moral commitments that had motivated it. In the 1990s he became an observant Jew, and his later philosophical work increasingly engaged with Jewish thought and the philosophy of religion.

Putnam published prolifically, often revising or abandoning earlier positions — a characteristic that frustrated commentators but that he considered a philosophical virtue. Died 13 March 2016 in Arlington, Massachusetts.

Philosophy of mind and language

Putnam’s work in the 1960s and 1970s reshaped the philosophy of mind and the philosophy of language before his turn toward realism and metaphysics.

Functionalism. In a series of papers beginning with “Minds and Machines” (1960) and “The Nature of Mental States” (1967), Putnam proposed that mental states are functional states — defined not by their physical composition but by their causal role in a system. Pain is whatever state plays the pain-role (caused by tissue damage, causes avoidance behaviour, produces distress). The proposal was liberating: it meant that mental states could be multiply realised — a silicon system that instantiated the same functional organisation as a brain would have the same mental states, regardless of the material difference. Functionalism became the dominant position in the philosophy of mind for two decades. Putnam himself turned against it in Representation and Reality (1988), arguing that the functional-state identity rests on the same assumption his later work challenged — that there is a single correct description of what a system is doing. If there is no unique computational description of a physical system (and Putnam argued there is not), then functionalism cannot identify mental states with computational states.

Twin earth and semantic externalism. “The Meaning of ‘Meaning’” (1975) introduced the twin-earth thought experiment. Imagine a planet identical to Earth in every respect except that the liquid in its oceans, lakes, and taps is not H₂O but a different chemical compound, XYZ, indistinguishable from water by ordinary observation. An English speaker on Earth and their twin on Twin Earth both use the word “water” — but they mean different things, because the word refers to different substances. The internal mental states of the two speakers are identical; the meanings are different. Putnam’s conclusion: “Cut the pie any way you like, ‘meanings’ just ain’t in the head.” Meaning is partly determined by the environment — by what is actually out there — not solely by what is in the speaker’s mind. The argument established semantic externalism as a major position in the philosophy of language and connected to broader questions about reference, natural kinds, and the relationship between mind and world.

Internal realism and conceptual relativity

Putnam’s early work defended scientific realism — the position that mature scientific theories are approximately true and that the entities they postulate (electrons, genes, fields) really exist. His “no miracles” argument: the success of science would be a miracle if scientific theories were not at least approximately true. This was the mainstream realist position, and Putnam articulated it more sharply than most.

He then turned against it. In Reason, Truth and History (1981) and the lectures collected in The Many Faces of Realism (1987), Putnam argued that metaphysical realism — the idea that there is one true and complete description of the world as it is “in itself,” independent of any conceptual framework — is incoherent. His model-theoretic argument: if the world determines the truth of our theories, and our theories have multiple models (interpretations that satisfy all the theory’s constraints), then there is no fact of the matter about which model is “the” correct one. Reference — the relation between words and things — cannot be fixed from a God’s-eye view, because there is no such view.

The alternative Putnam developed is internal realism: truth and reference are determined within a conceptual scheme, not from outside it. What counts as an object, what counts as a property, what counts as a fact — these depend on the conceptual framework in use. This is not relativism, because the world constrains what we can say (not all schemes are equally good), and rationality provides standards for choosing between descriptions (coherence, simplicity, empirical adequacy). But it is pluralist: multiple conceptual schemes can be equally valid descriptions of the same reality.

Conceptual relativity. The concept that makes the position work. Putnam’s favourite example: consider a world with three individuals — A, B, C. How many objects are in this world? The answer depends on the conceptual scheme. A mereologist who counts sums as objects gets seven (A, B, C, A+B, A+C, B+C, A+B+C). A philosopher who counts only individuals gets three. Both descriptions are correct; neither is privileged; they are not competing answers to the same question but answers to different questions framed by different schemes. Conceptual relativity is not the claim that truth is relative — it is the claim that the question “how many objects exist?” has no scheme-independent answer.

The debate with Donald Davidson. Davidson’s “On the Very Idea of a Conceptual Scheme” (1974) argued that the notion of alternative conceptual schemes is incoherent — that we cannot make sense of a language we cannot translate, and that apparent incommensurability is always resolvable. This is a direct challenge to Putnam’s position. Putnam responded by distinguishing conceptual relativity (different but mutually translatable descriptions) from conceptual incommensurability (untranslatable frameworks). Conceptual relativity does not require untranslatability — it only requires that different schemes carve the world differently and that neither carving is uniquely correct. The debate is unresolved and structurally significant: it turns on whether plurality of description is a genuine feature of reality or an artefact of our notation.

The collapse of the fact/value dichotomy

Putnam’s later work — particularly The Collapse of the Fact/Value Dichotomy (2002) and Ethics without Ontology (2004) — argued that the sharp separation of facts and values inherited from logical positivism is untenable. “Thick” ethical concepts — cruel, courageous, just — are simultaneously descriptive and evaluative; they cannot be factored into a purely descriptive component and a purely evaluative add-on. The entanglement runs deeper: the selection of which facts are relevant, the standards of what counts as a good explanation, the criteria for simplicity and coherence in science — these all involve value judgments. Science is not value-free, and ethics is not fact-free. The dichotomy, Putnam argued, was not a discovery but an assumption of a particular philosophical tradition (logical positivism), and its collapse opens space for a more honest account of both science and ethics.

Where Putnam stops

Internal realism was designed to occupy the ground between metaphysical realism and relativism. Whether the ground is stable has been the central question in Putnam’s reception. Putnam himself abandoned the label “internal realism” in the 1990s, moving toward what he called “natural realism” or “pragmatic realism” — a position closer to the commonsense realism of James and the direct perception of ordinary experience. The shift acknowledged a problem: internal realism, by making truth internal to a conceptual scheme, risked the same scheme-dependence it attributed to metaphysical realism. If truth is what is ideally justified within a scheme, and schemes can differ, then internal realism looks like a sophisticated relativism — exactly the position Putnam set out to avoid.

The model-theoretic argument Putnam deployed against metaphysical realism has been turned back against his own position. If reference cannot be fixed from a God’s-eye view, how does internal realism fix it from inside? The answer — that reference is fixed by our practices, by the way we use words in the world — is pragmatist, and it is the direction Putnam moved. Whether pragmatic realism is a stable resting point or a further way station depends on whether “our practices” can bear the philosophical weight placed on them — a question Rorty answered differently than Putnam did.

Conceptual relativity faces a parallel pressure. If different schemes carve the world differently and neither is privileged, what constrains the schemes? Putnam’s answer is rational acceptability — coherence, simplicity, empirical adequacy — but these criteria are themselves conceptually mediated, which threatens a regress. The question of what makes one scheme rationally superior to another, without invoking either a God’s-eye view or mere convention, is the open problem that runs through all of Putnam’s phases.

Key works

See also: Rorty · Goodman · James