Putnam, of all people

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Hilary Putnam Philosopher who revolutionised the philosophy of mind
 Hilary Putnam was constantly critical of his own theories
 Hilary Putnam was constantly critical of his own theories
The American philosopher Hilary Putnam, who has died aged 89, transformed the philosophy of mind, the philosophy of language, metaphysics and epistemology. By focusing on the role, rather than substance, of mental states, his theory of functionalism offered a plausible solution to the mind-body problem. With his theory of externalism – “meanings just ain’t in the head” – he dislodged the subjective starting point that had ruled philosophical theories of meaning since Descartes. And he made huge contributions to the philosophy of science, philosophy of mathematics, and to maths itself.

But he was famous, too, for forever changing his mind. Constantly critical of his own theories, he repudiated functionalism in the 1980s, and went through a gamut of views on metaphysics, as he did in his personal life on politics, although always remaining on the left. The one constant in his fertile fluctuations was his agility in thinking outside the set boundaries of any topic he tackled, and in resetting those boundaries. As a professor at Harvard from 1965 onwards, he was determined to accommodate both a scientific and a human, commonsensical viewpoint, and his numerous papers and books were full of vivid thought-experiments.

Hilary was born in Chicago. His father, Samuel – a scholar of Romance languages, who translated Rabelais and Don Quixote – was a Communist until 1956, and wrote a column for the Daily Worker. Hilary’s mother, Riva (nee Sampson), was Jewish, but the family were secular. Having moved to France – Putnam’s first language was French – they returned to live in Philadelphia in 1934. One of Putnam’s fellow pupils at school was Noam Chomsky, who remained a friend and sparring-partner throughout his life.

After graduating in philosophy and mathematics at the University of Pennsylvania in 1948, Putnam began a PhD at Harvard, under Willard Van Orman Quine. He finished it at UCLA in 1951, taught by Hans Reichenbach and Rudolf Carnap, whose Logical Positivism had dominated American philosophy for the previous 15 years. Putnam attacked their scientism – giving primacy to empirical science, to the exclusion of other viewpoints – while forever acknowledging his debt to Reichenbach and remaining close friends with Carnap. He also combated Quine’s views in his 1957 paper The Analytic and Synthetic, but collaborated with him to produce the Quine-Putnam indispensability thesis in mathematics. Putnam’s first teaching posts were in maths and philosophy, at Northwestern University (1952-53) and Princeton (1953-61) and then as professor of the philosophy of science at the Massachusetts Institute of Technology (MIT, 1961-65) until his move to Harvard as professor of philosophy.

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In a series of brilliant papers, beginning with Minds and Machines (1960), Putnam disputed both Behaviourism and Type-Identity theory, each of which seeks, in line with scientific respectability, to reduce mental states – pain, beliefs, thoughts – to something physical. Behaviourism claims that mental states are simply what we do, or are inclined to do, in certain circumstances (being in pain, for instance, is the way we typically react to physical injury by flinching from its cause, crying out, and seeking respite), and Putnam had great fun at this theory’s expense with a thought-experiment of poker-faced super-Spartans.

His real fire, however, was reserved for the then-paramount Type-Identity theory, which holds that, in the course of scientific discovery, mental states will “turn out to be” particular types of brain states, just as heat has transpired to be molecular motion and water to be H2O. What this entails, said Putnam, is that only creatures with our type of brain have conscious experience. Yet surely mental states like pain and believing are “multiply realisable” – in rats, octopuses, snakes and (in principle) Martians.

“The all too old question of matter or soul-stuff” is the wrong question, he maintained. The essential thing to look at is not whatever constitutes mental states, but how they function as part of an overall system. In fact what they are is what they do – they are “simply our organisation-to-think, feel, desire, need …”. So forget the hardware, look at the software, which can “be realised in a bewildering variety of different ways” – silicon, neurons or tentacles. “We could be made of Swiss cheese and it wouldn’t matter.”

Pain, for instance, is the same functionally, though different physically, in a human, a dog and an octopus – whatever induces each of them to register, avoid and ameliorate any damage that that particular organism incurs. Putnam’s machine-state functionalism seemed to combine the most cogent features of Behaviourist and Identity theories, while apparently avoiding their pitfalls. It was hugely acclaimed (and of course attacked), and was seminal in modern cognitive science.

While revolutionising philosophy of mind, Putnam was involved with revolutionary politics. At MIT in 1963, he organised one of the first faculty and student committees against the Vietnam war, and at Harvard he organised campus protests, publicly burned draft cards, and acted as official faculty adviser to Students for a Democratic Society (the main anti-Vietnam war organisation). In 1965 he became a member of the Progressive Labor party (promoting, in his own words, an “idiosyncratic version of Marxism-Leninism”), and would stand outside factory gates at 7am to sell the magazine Challenge and discuss politics with the workers.

On campus he disrupted the classes of Richard Herrnstein (co-author of the allegedly racist Bell Curve: Intelligence and Class Structure in American Life), and he lived in a commune with students. He was a brilliant, captivating teacher, but for a time his students had to spend his lectures twisted round to look at him because he refused to sit at the front; although, in his more dogmatic Marxist phase, he spoke on a podium and advised students to read Mao Zedong’s Little Red Book. The Harvard establishment was in despair.

To their relief, Putnam left Progressive Labor in 1972. Simultaneously he was beginning to reject scientific realism, which claims that reality is independent of mind and language, and to develop his theory of semantic externalism, which argues that meaning is not a matter of subjective mind-set, nor of an objective match between word and object, but a social phenomenon. A now-famous thought-experiment in his paper The Meaning of “Meaning” (1975) imagined a planet that precisely duplicates ours except that the clear liquid which its inhabitants drink and swim in (and also, in their doppelgänger English, call “water”) is not H2O but has a different chemical constitution, XYZ. Both Oscar on Earth and Oscar on Twin Earth are “molecule for molecule identical”, therefore in exactly the same mental state (whatever that involves psychologically and neurally) when they think, or talk, of “water”. Yet, Putnam argued, Oscar would not mean water if he is thinking and talking about the stuff that Twin-Earthers call “water”. Meaning, then, depends on external states of affairs; but the nature of these, in turn, is relative to language. “Thus the world is both ‘objective’ and not ‘objective’; we cannot ask what is the case without choosing some system of concepts (and no one system is uniquely fitted to describe ‘the world’); but once we have a system of concepts in place, what is true or false is not simply a matter of what we think.”

It is as if “water”, like “tiger”, “elm”, “gold” and other “natural kind terms” in a language, are, for speakers of that language, fixating baptisms, the fixity of which is irrelevant to the original baptisers – and subsequent namers – actually knowing the nature or inner constitution of whatever has been named. Such right-the-way-down knowledge will develop (as with the 18th-century discovery that water is H2O) and can be left to experts, thanks to what Putnam calls “the division of linguistic labour”; which is what also enables Putnam himself, despite his total ignorance of what an elm tree looks like, successfully to talk and think about elms. Externalism both out-relativises the relativists yet also out-objectivises the objectivists. A huge industry has grown up around it, ringing the changes on Putnam’s first exposition.

Putnam’s new position on meaning entailed a new position on metaphysics and outlawed the possibility of total scepticism. In Brains in a Vat (1981), he discussed the modernised version of Descartes’ evil demon thought-experiment, in which the sceptic asks if, although having sense experiences like those of a normally embodied human, she might not just be a brain in a vat. The sceptic’s question, said Putnam, does not even make sense – given that she belongs to no linguistic community, thanks to her envattedness, she would not be referring to a brain when saying “brain”, or to a vat when saying “vat”.

In 1976, Putnam was elected president of the American Philosophical Association, and soon afterwards was made professor of mathematical logic. In the 1980s he became increasingly dissatisfied with functionalism – it conflicted with his theory of externalism, and was, he had come to think, too scientistic. He began to write about ethics and Jewish philosophy, and to pursue his Jewish roots (he learned Hebrew, and had a barmitzvah at the age of 68). Some philosophers were saddened by his turning to pragmatism and also to mainland European philosophy (perhaps in keeping with that, commented an old student, he began to smoke a pipe). Others thought he was doing his best work.

Having taught at Harvard for 35 years, Putnam retired as emeritus professor in 2000. He continued to teach and write, but also devoted himself to tending his vegetable garden with his second wife, Ruth Anna (nee Jacobs, also a philosopher), and creating ratatouille and soups from its products. He held several honorary degrees, and was a fellow of the American Academy of Arts and Sciences and of the American Philosophical Society. In 2011 he was awarded the Rolf Schock prize in logic and philosophy by the Royal Swedish Academy of Sciences, and he continued to publish until 2014.

Putnam always said that the best minds are those that think through a position, get to the other side of it, and then reject it. He certainly did that himself, but the same preoccupations persisted throughout his work, as did his intense pleasure in thought. After reading aloud from some philosopher’s work in a lecture, he would let out a wonderful raucous laugh of delight.

In 1948 he married Erna Diesendruck, and they had a daughter, Erika. That marriage ended in divorce in 1962, and later that year he married Ruth Anna, with whom he had a daughter, Polly (“Max”), and two sons, Sam and Josh. He is survived by Ruth Anna, his four children and four granddaughters.

• Hilary Whitehall Putnam, philosopher, born 31 July 1926; died 13 March 2016

• This article was amended on 15 March 2016. Silicon is the material involved in the discussion of mental states, rather than silicone.