QuestionsIs the mind the brain?If pain were a brain state it would be so necessarily: yet we can conceive it without one
Is the mind the brain?The mind is not matter

If pain were a brain state it would be so necessarily: yet we can conceive it without one

Kripke's modal argument against the identity theory

Saul Kripke 1940 · 2022If pain were identical to a brain state, it would be so necessarily; yet one can conceive one without the other.
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What it claims

Pain is not identical to a brain state (the type-type identity theory is false). For Kripke, this tells heavily against the usual forms of materialism, without proving that no other version works.

Why

If pain and a brain state were identical, they would be so necessarily; yet we can conceive one without the other, and not as an illusion.

The same idea through history
René Descartes1641Descartes holds that what we can clearly conceive without something else can exist without it. He concludes that the mind is distinct from the body. Kripke takes up this form of argument, but only against the identity of pain with a brain state.
Saul Kripke1980Kripke (lectures of 1970, published in 1972 and as a book in 1980) shows that the identity of pain with a brain state, if true, would be necessary. He remains careful: he does not assert dualism, he says the usual analogies do not save the identity theory.
In short

"If pain were a brain state it would be so necessarily: yet we can conceive it without one" is an argument by Saul Kripke (Naming and Necessity, 1980, Lecture III, 1980) on the question "Is the mind the brain?" (answer: the mind is not matter). Its claim: Pain is not identical to a brain state (the type-type identity theory is false). For Kripke, this tells heavily against the usual forms of materialism, without proving that no other version works. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 4 premises. AskPhilosophy presents 2 objections, 0 of them with a documented reply, and the original text behind each premise, checked word for word.

Naming and Necessity, 1980, Lecture III
Valid

Water is H2O and lightning is an electric discharge: these are discoveries of science, and yet, says Kripke, they could not have been otherwise. If pain were identical to a brain state, the same would hold: necessarily. Yet it seems quite possible to be in pain without that state, or to be in that state without pain. For water, this impression of possibility can be explained as an illusion. For pain, says Kripke, it cannot. Note: Kripke does not claim that the mind is immaterial. He rejects the identity of pain with a brain state, and says this tells heavily against the usual forms of materialism.

P1The words "pain" and "C-fiber stimulation" (a brain state) are rigid designators: they designate the same thing in every possible situation. A pain is essentially a pain.
P2If two rigid designators designate the same thing, the identity is necessary. So if pain is identical to that brain state, there is no possible situation where one exists without the other.
P3Yet it seems possible for one to exist without the other: the correspondence between a brain state and a mental state seems to have an obvious element of contingency.
P4This appearance of possibility cannot be explained away as it is for heat or water. In those cases, what seems possible is that the phenomenon exists without being felt as heat (or without the appearance of water). For pain, it would be a brain state existing without being felt as pain, that is, without pain at all, which contradicts the identity. Pain is picked out by its felt quality itself, which is an essential property.
P5 · implicit premiseIf something seems possible and this appearance cannot be explained away as an illusion, then it really is possible. (Hill, summing up the argument, presents it as a premise of Kripke's.)
Therefore pain is not identical to a brain state (the type-type identity theory is false). For Kripke, this tells heavily against the usual forms of materialism, without proving that no other version works.

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 P5, one could accept that it seems possible without concluding that it is possible. One would say that our imagination is a poor judge, like someone imagining that a chair could be made with no matter. This is exactly the position of Hill and Loar.
The argument is valid. Suppose pain is identical to the brain state: by P1 and P2 the identity is necessary, so no possible situation separates them. But P3, P4 and P5 say that such a situation is possible. Contradiction: the identity is therefore false. The objections target P4 (can the appearance be explained otherwise?) and P5 (is conceiving enough to say it is possible?).
Analogy. We can imagine a world where a clear drinkable substance fills the lakes but is not H2O: this world is possible, but it is not water. For pain, says Kripke, this kind of distinction does not work: a "fake pain" that does not hurt is not a pain.

Objections

2

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

C
Christopher Hill 1997 · attacks premise 4

Hill accepts the reconstruction of the argument, but says Kripke nowhere defends the idea that the water and heat model is the only way to explain an appearance of possibility. According to him, the impression that we can imagine pain without a brain state comes from two kinds of imagination working separately: the "sympathetic" imagination, which puts us in a state like the one we have when we feel pain, and the "perceptual" imagination, which can form the image of a situation with no brain process. We can splice them together without incoherence, but that does not show it is objectively possible.

no reply
We have not yet found a direct reply by Kripke in the texts.
The debate goes on (our summary) The debate goes on (our summary). Hill himself notes that Kripke's argument still has serious supporters (he names Hart, Yablo and Chalmers).
B
Brian Loar 1990 · attacks premise 4

Loar grants that the identity between a sensation state and a brain state is an a posteriori identity, but denies that it must be explained as for water. Sensation concepts ("this pain") are recognitional concepts that refer directly to their physical property, without going through an appearance that could come apart from it. The identity is true and necessary, yet it does not seem obvious, because we have two kinds of concepts of the same state. The appearance of possibility comes from that.

no reply
Kripke did reply, but that text is not yet in our corpus.
The debate goes on (our summary) The debate goes on (our summary, second-hand: Loar's article could not be consulted). Supporters of Kripke and Chalmers answer that this "phenomenal concepts" strategy only moves the problem: we still need to explain why the identity remains so surprising to us, when water and H2O no longer are.