Chicago 1926 – Arlington, Massachusetts 2016

Hilary Putnam

What makes a state a pain is not what it is made of but what it does: caused by damage, causing distress and avoidance, linked to other states in a characteristic pattern. Anything with that pattern would be in pain, whether its parts were neurons, silicon chips or something stranger.

The view

Putnam was one of the most wide-ranging philosophers of the twentieth century, working on mathematics, logic, language and science, and he had a habit of changing his mind in public. In the 1960s he set out the theory that became the dominant view of the mind for a generation: functionalism. Its classic statement is "Psychological Predicates" (1967), later reprinted as "The Nature of Mental States".

Putnam compared minds to computing machines. A computer program can be described abstractly, as a table of states and transitions, without saying anything about the hardware that runs it: the same program can run on valves, transistors or gears. Mental states, he proposed, are like the states of such a program. To be in pain is to be in a state defined by its causal role: typically caused by bodily damage, typically causing distress, a wish for it to stop, wincing and avoidance, and related in characteristic ways to other mental states.

The argument

An octopus can feel pain, though its nervous system is built very differently from ours. After Putnam, "Psychological Predicates" (1967)

Putnam's argument against the identity theory was simple and influential. If pain were identical to one kind of brain process, say the firing of certain fibres, then any creature without those fibres could not feel pain. But mammals, birds, reptiles and octopuses have very different nervous systems, and it is implausible that none but us can feel pain. A Martian or a robot might too. Mental states are multiply realisable: the same state can be realised in different physical stuff. So pain cannot be one physical state; it must be a functional one. Swap the hardware in the figure and watch what stays the same.

Putnam later turned against his own theory. In Representation and Reality (1988) he argued that functional organisation is too abstract to fix what a mind is about. His "Twin Earth" thought experiment (1975) had already suggested that meanings "ain't in the head": what your words refer to depends partly on your environment, not just your inner organisation. Functionalism outlived its founder's doubts and became the working assumption of much of cognitive science.

Where he meets Dennett

Dennett is a functionalist through and through. His intentional stance, his multiple drafts and his illusionism all assume that a mind is defined by what it does, not by its material. He agreed with Putnam that a machine with the right organisation would have a mind, and that nothing about carbon is magic.

Where they part

Putnam's early functionalism was neat: a mind is a machine table, a definite list of states and transitions. Dennett thought real minds were much messier. They are evolved, improvised, full of competing subsystems and half-finished drafts, more like a crowd than a program. He also refused to put a sharp boundary round "the functional level". Function goes all the way down, he said, and how much hardware detail matters depends on what job you are describing. And where Putnam came to doubt that functional organisation could fix meaning, Dennett accepted the point cheerfully: meaning was always a matter of interpretation from the intentional stance, never something stamped inside the head.

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Further reading

• Hilary Putnam, "The Nature of Mental States" (1967), in his Mind, Language and Reality: Philosophical Papers, vol. 2 (Cambridge, 1975).
• Peter Godfrey-Smith, Other Minds: The Octopus and the Evolution of Intelligent Life (William Collins, 2016): the octopus in the flesh.
• Hilary Putnam, Representation and Reality (MIT Press, 1988): the founder's second thoughts.
• Functionalism, Stanford Encyclopedia of Philosophy.