Hilary Whitehall Putnam was born in Chicago, Illinois, in 1926. He was politically progressive throughout his life, an active supporter of the American Civil Rights movement and an opponent of American military intervention in Vietnam. As a matter of principle, he maintained that academics have a particular ethical responsibility to society at large, a view that is evident in his social and political writings. Through his academic work, he made significant contributions to philosophy, mathematics and computer science. In 2011 he was awarded the Rolf Schock Prize in Logic and Philosophy and in 2015 he was awarded the Nicholas Rescher Prize for Systematic Philosophy. At the time of his death, in 2016, aged eighty-nine, he was Cogan University Professor Emeritus at Harvard University, where he had spent most of his career.
Putnam’s work ranges over an exceptionally diverse set of philosophical issues, but it is his work in the philosophy of language that has arguably had the greatest effect on the discipline. Putnam argues against a traditional, “individualist” understanding of language, according to which what you mean by a word depends on how you, as an individual, use that word. In “Meaning and Reference” (1973), he claims that traditional semantic theory ignores two elements that are fundamental to a proper account of language – “the contribution of society and the contribution of the real world”.
The contribution of society provides a stability to word-meaning across a linguistic community whose individual members have varying degrees of linguistic competence. Putnam illustrates the point when he says that although he cannot distinguish an elm from a beech, he still means elm by “elm” and beech by “beech” because he is part of a linguistic community with other people (the experts) who can distinguish elms from beeches. This is the phenomenon of linguistic deference. Different people count as the relevant experts for different terms (“typhoon”, “atomic mass”, “hip-hop”, “software”, “soufflé”), and the rest of us, without being consciously aware of doing so, defer to the relevant experts in order to secure our meanings. The phenomenon is widespread and is crucial for language-learning.
The contribution of the real world is illustrated by Putnam’s influential “Twin Earth” thought experiment. Twin Earth is a place just like Earth, except for the fact that the watery stuff that runs in the rivers and fills the lakes and seas is not water (H2O) but “twin water”, a superficially similar liquid with a different molecular structure (XYZ). We are asked to imagine two ordinary individuals in 1750 – Oscar, on Earth, and his doppelgänger, Twin Oscar, on Twin Earth, before the molecular structure of water (or twin water) was discovered. Twin Oscar is Oscar’s doppelgänger in the strong sense that he has the same experiences and feelings, he has the same capacities to discriminate between different objects and kinds, and he makes the same gestures, movements and sounds. Effectively, Oscar and Twin Oscar live out the same lives in different places. The only difference between them is that Oscar lives in a world with water (H2O), whereas Twin Oscar lives in a world with twin water (XYZ). This difference in their environments is enough, says Putnam, to affect what they are talking about. When Oscar uses the word “water” he is talking about water, whereas when Twin Oscar uses the word “water” he is talking about twin water. As a result, what you mean depends in part, but crucially, on the world around you.
As Putnam famously writes in “The Meaning of ‘Meaning’” (1975), “cut the pie anyway you like, ‘meanings’ just ain’t in the head”. The view is known as “semantic externalism”, because the meanings of an individual’s words depend on relations between her and her social and physical environment, both of which are traditionally seen as “external” to her as an individual. Because of the intimate connection between language and thought, the view has straightforward implications for the philosophy of mind. If what you mean by your words depends on your social and physical environment, then what you think will also do so: Oscar thinks that water is refreshing; Twin Oscar thinks that twin water is refreshing. The externalist view applied to the contents of thought is known as “content externalism”.
There are some who reject the implications of Putnam’s Twin Earth thought experiment, but I doubt there is a single philosopher in the analytic tradition who has not heard of Twin Earth, and the impact of the externalist view of language and mind both within philosophy and beyond is undeniable. Its influence has been felt in metaphysics, epistemology and moral theory, with the subsequent creation of “Moral Twin Earth”, and it has undoubtedly laid the groundwork for one of the most exciting and innovative research programmes in cognitive science: embodied, embedded, extended and enactive (4E) cognition. What is significant about the research programme in cognitive science is the rejection of the apparently-clear divide between us as individual cognizers and the world around us.
Putnam also made significant contributions to the mind–body problem, a fundamental philosophical question: how does the mind, understood as the locus of thought and conscious experience, relate to the body, understood as a physical organism governed, ultimately, by the laws of physics? By the time Hilary Putnam focused on the problem in the 1960s, three alternative solutions had emerged: dualism, behaviourism and materialism. According to dualism, the mind is an immaterial substance that “inhabits” the body, causing it to move, rather as a puppeteer moves an otherwise inanimate puppet; according to behaviourism, mental states, such as experiencing pain, are really just behavioural states such as wincing and limping; and according to materialism, mental states are really just physical states, typically understood as states of the brain or central nervous system. Putnam argued against all three, and in so doing introduced a far more plausible alternative that continues to dominate philosophy of mind in one form or another to this day.
The fundamental problem with dualism has been well known since Princess Elisabeth of Bohemia articulated it in her correspondence with Descartes: how can a mind, conceived of as an immaterial substance with no physical properties – no spatial dimensions, no mass – cause a physical body to move? Descartes had no plausible answer, and the general consensus, at least among philosophers, is that there is no plausible answer to be had – that there is little sense to be made of the claim that mental states, such as thoughts, feelings and emotions, are states of an immaterial substance.
The fundamental problem with behaviourism, as Putnam pointed out, is that it identifies mental states with behaviour when it is clearly more plausible to think of mental states as the causes of behaviour. In his “Brains and Behavior” (1963) Putnam illustrates this point through an instructive analogy with diseases. A disease, such as polio, is not to be identified with a collection of symptoms, but is, rather, an underlying virus that causes those symptoms. So too, the state of pain that is induced when I stub my toe is not to be identified with my wincing and limping, but is, rather, a distinct state that causes my wincing and limping. Mental states are therefore not behavioural states.
The most influential aspects of Putnam’s reflections on the mind–body problem, however, come from his argument against materialism, coupled with his positive proposal that a mental state is, as he says in “The Nature of Mental States” (1967), “not a brain state, in the sense of a physical-chemical state of the brain (or even the whole nervous system) but another kind of state entirely . . . a functional state of a whole organism”.
The basic point is that different organisms with different physical structures are capable of the same kinds of mental states. As Putnam notes, an octopus is surely capable of feeling pain despite the fact that it does not have the same physical brain structure or central nervous system as a human. The point generalizes. Mental states are defined not by their physical structure, but by their function (their causes and effects). Pain is the state that (under normal circumstances) is caused by bodily damage and causes avoidance behaviour; the desire for water is the state (again, under normal circumstances) that is caused by dehydration and causes one to engage in water-seeking behaviour. Mental states conceived as functional states can accommodate the fact that mental states are, as Putnam’s examples are intended to show, “multiply realizable” across a range of different physical structures. Multiple realization is a common phenomenon in the natural world – plenty of creatures have eyes that have different physical structures; and it is a common feature of artefacts – plenty of bottle openers have different physical structures. So it is, according to Putnam, with mental states.
The view that mental states are multiply realizable functional states is known as “functionalism”, and provides a fourth, more plausible solution to the mind–body problem. Putnam, in “Brains and Behavior”, writes “This fourth alternative is materialistic in the wide sense of being compatible with the view that organisms, including human beings, are physical systems consisting of elementary particles and obeying the laws of physics, but does not require that such ‘states’ as pain and preference be defined in a way which makes reference to either overt behavior or physical-chemical constitution”.
Functionalism renders the relation between the mind and the body directly analogous to the relation between a computer programme and the hardware required to run it: just as the same programme can be run on different machines with different physical structures, the same type of mental state can occur in different organisms with different physical structures. It is a prominent theme in Putnam’s writing that reflection on computers of certain kinds can shed light on the nature of the human mind. Specifically, Putnam thought that such reflection undermines the mystery surrounding the human mind. For example, in “The Mental Life of Some Machines” (1967) he says “the conceptual issues surrounding the traditional mind–body problem have nothing to do with the supposedly special character of human subjective experience, but arise for any computing system of a certain kind of richness and complexity, in particular for any computing system able to construct theories concerning its own nature”. And in “Minds and Machines” (1960) he even dismisses, with characteristic candour, the claim that the mind–body problem raises a substantive issue, contending “for it is quite clear that no grown man in his right mind would take the problem of the ‘identity’ or ‘non-identity’ of logical and structural states of Turing machines at all seriously – not because the answer is obvious, but because it is obviously of no importance what the answer is. But if the so-called ‘mind–body problem’ is nothing but a different realization of the same set of logical and linguistic issues, then it must be just as empty and just as verbal”.
Sarah Sawyer is Professor of Philosophy at the University of Sussex
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