QuestionsIs the mind the brain?Pain can be realized by very different bodies: it is therefore not a particular brain state
Is the mind the brain?The mind comes from matter

Pain can be realized by very different bodies: it is therefore not a particular brain state

Multiple realizability (Putnam's functionalism)

Hilary Putnam 1926 · 2016The same mental state can be realised by very different brains: the mind is a function, not a stuff.
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What it claims

Pain is not a physical-chemical state of the brain: it is a functional state of a whole organism.

Why

Octopuses, humans, aliens or machines can suffer without sharing one brain state: pain depends on function, not on matter.

The same idea through history
Hilary Putnam1967Putnam proposes that pain is a functional state of the whole organism. He notes that this thesis, which is "mechanistic" in inspiration, is nevertheless not incompatible with dualism: it says what a mental state does, not what it is made of. We file it under materialism because, in common use, its defenders think the systems that realize mental states are physical.
In short

"Pain can be realized by very different bodies: it is therefore not a particular brain state" is an argument by Hilary Putnam ("Psychological Predicates" ("The Nature of Mental States"), 1967, 1967) on the question "Is the mind the brain?" (answer: the mind comes from matter). Its claim: Pain is not a physical-chemical state of the brain: it is a functional state of a whole organism. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 5 premises. AskPhilosophy presents 3 objections, 1 of them with a documented reply, and the original text behind each premise, checked word for word.

"Psychological Predicates" ("The Nature of Mental States"), 1967
Valid

The identity theory says that pain is a certain brain state. But an octopus, whose brain is very different from ours, also seems to suffer. And if we ever meet extraterrestrials or build machines that suffer, their "brain" will again be something else. In 1967 Hilary Putnam concludes that pain cannot be one precise physical state: it is a functional state, defined by what it does (what causes it, what it brings about, its links with other states). This idea, functionalism, became the dominant theory of mind. It is compatible with physicalism (any system that realizes pain is physical) but does not require it by itself.

P1Pain is felt by organisms of very different kinds: mammals, reptiles, molluscs such as the octopus, and perhaps beings from elsewhere or machines.
P2It is extremely probable that these systems are not all, when in pain, in the same physical-chemical brain state. It is enough to find a single psychological state, for example being hungry, shared by a mammal and an octopus but whose physical correlate differs.
P3If pain were identical to a type of physical-chemical brain state, that state would have to be a possible state of a mammalian, a reptilian and a mollusc's brain, and not be possible in any creature that cannot feel pain. Pain would then have the same physical state in all of them.
P4Identity cannot be saved by calling the mere list of all these different states "a single physical state": this is an ad hoc move, which does not have to be taken seriously.
P5It is more likely that the functional state (defined by its causes, effects and links with other states) is always correlated with pain, whatever the species, than a physical-chemical brain state or a behavior disposition.
Therefore pain is not a physical-chemical state of the brain: it is a functional state of a whole organism.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P4, a defender of identity could say that pain is the "disjunctive" state: C-fibers in humans, something else in the octopus, something else in the machine. This is the strategy Putnam considers ad hoc and that Kim discusses at length.
The argument is valid: P1 and P2 say that pain exists in beings whose physical states differ; P3 and P4 say that identity with a single physical state would require the opposite; so identity is set aside; P5 adds that the functional solution is the best remaining one. The debate is about P2 (are the differences as large as claimed?), the scope of the conclusion (does it refute all reduction?) and P5 (is a state defined by its effects alone enough?).
Analogy. A corkscrew can be made of metal, plastic or wood, in many shapes. Being a corkscrew is not being made of one particular material, it is serving to open bottles. Putnam says the same of pain: what matters is its role, not the stuff.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

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Jaegwon Kim 1992 · attacks the conclusion

Kim does not dispute multiple realizability, but denies that it refutes the reduction of the mental to the physical. If pain is realized differently in humans, reptiles and Martians, the psychology of each species (or structure type) can be reduced to its own physics: a "local" reduction. Bridge laws restricted to a species are enough.

Putnam replies
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Jaegwon Kim 1992 · What Kim himself concedes
Kim admits the price of his position: after several local reductions, pain as a kind common to all species does not survive. He asks whether this is so bad, comparing with jade (which turned out to be two different minerals).
The debate goes on (our summary) The debate goes on (our summary). Putnam thought pain is a single kind, useful to the science of mind; Kim replies that, if it is realized in very different ways, it is not a genuine scientific kind. Functionalists hold that psychology keeps its explanatory value even if it does not reduce to the physics of one species.
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William Bechtel and Jennifer Mundale 1999 · attacks premise 2

Multiple realizability is overstated. It is obtained by comparing psychological states described coarsely ("being in pain") with brain states described very finely. If one uses the same degree of precision on both sides, as neuroscientists do when they identify brain areas by comparing species, many similarities appear. According to them, neuroscience therefore keeps a role in understanding cognition.

no reply
We have not yet found a direct reply by Putnam in the texts.
The debate goes on (our summary) The debate goes on (our summary). Kenneth Aizawa replied to this article in 2009 (Synthese), and the literature on the point is large. Defenders of multiple realizability hold that one can always find a species or a possible machine where the same function rests on another structure; their opponents hold that this possibility remains science fiction.
Hilary Putnam himself 1988 · attacks the conclusion

Putnam later abandons functionalism. In Representation and Reality (chapter 5, "Why Functionalism Didn't Work"), he explains why, in his view, functionalism did not work as a theory of mind. His argument against identity with a precise brain state remains famous, but he no longer defends the positive thesis he drew from it, pain as a functional state.

no reply
We have not yet found a direct reply by Putnam in the texts.