Monday, November 2, 2020

Pain and water

One way for physicalists to handle the apparent differences between mental and physical properties is to liken the difference to that between water and H2O. It is a surprising a posteriori fact that water is H2O. Similarly, it is a surprising a posteriori fact that pain is physical state ϕ135 (say).

Now, a posteriori facts are facts that are knowable by observation. But it is not clear that the proposition that pain is physical state ϕ135 is knowable by observation.

Here is why. There are two main candidates for what kind of a state ϕ135 could be: a brain state or a functional state. The choice between these two candidates depends on how strongly one feels about multiple realizability of mental states. If one is willing to say that only beings with brains like ours—say, complex vertebrates—feel pain, one might identify ϕ135 with a brain state. If one has a strong intuition that beings with other computational systems anatomically different from those of complex vertebrates—cephalopods, aliens, and robots—could have consciousness, one will opt for identifying ϕ135 as a functional state.

But in fact, assuming pain is a physical state, there is a broad spectrum of physical state candidates for identifying pain with, depending on how far we abstract from the actual physical realizers of our pains while keeping fixed the broad outlines of functionality (signaling damage and leading to aversive behavior). If we abstract very little, only brain states found in humans—and perhaps not all humans—will be pain. If we abstract a bit more, but still insist on anatomical correspondence, then brain states found in other complex vertebrates will be pain. If we drop the insistence on anatomical correspondence but do not depart too far, we may include amongst the subjects of pain other DNA-based organisms such as cephalopods. Further abstraction will let in living organisms with other chemical bases, and yet further abstraction will let in robots. And even when talking of the fairly pure functionalism applicable to robots, we will have serious questions about how far to abstract concepts such as “damage” and “aversive behavior”.

The question of where in this spectrum of more and more general physical states we find the state that is identical with pain does not appear to be a question to be settled by observation. By internal observation, we only see our own pain. By external observation, however, we cannot tell where in the spectrum of more and more general (perhaps along multiple dimensions) physical states pain is present, without begging the question (e.g., by assuming from the outset that certain behaviors show
the presence of pain, which basically forces our hand to a functionalism centered on those behavior).

Objection 1: An experimenter could replace the brain structures responsible for pain in her own brain by structures that are further from human ones, and observe whether she can still feel pain. Where the feeling of pain stops, there we have abstracted too far.

Response: There are serious problems with this experimental approach. First, mere replacement of brain pain centers will not allow one to test hypotheses on which what constitutes pain depends on the larger neural context. And replacement of the brain as a whole is unlikely to result in the experimenter surviving. Second, and perhaps more seriously, if replacements of the brain pain centers commit the same data to memory storage as brain pain centers do, after the experiment the agent will think that there was pain, even if there wasn’t any pain there, and if they have the same functional influence on vocal production as brain centers do, the agent will report pain, again even if there wasn’t any pain there.

Objection 2: We could know which physical state pain is identified with if God told us, and being told by God is a form of a posteriori knowledge.

Response: It seems likely that God’s knowledge of which physical states are pains, or of the fact that water is H2O, would be a priori knowledge. God doesn’t have to do scientific research to know necessary truths.

Objection 3: We can weaken the analogy and say that just as the identity between water and H2O is not a priori, so too the identity between pain and ϕ135 is not a priori, without saying that both are a posteriori.

Response: This is probably the move I’d go for if I were a physicalist. But by weakening this analogy, one weakens the position that it defends. For it is now admitted that there is a disanalogy between water-H2O and pain-ϕ135. There is something rather different about the mental case.


Michael Gonzalez said...

What does it mean for pain to be a "physical state"? Pain is not a substance of any kind, so the comparison to water (which is a substance) being identified with a certain chemical construction seems out of place. If we assemble hydrogen and oxygen atoms in a certain way, these assemblages themselves start to flow and behave as water is known to do. They just are small pieces of water. But, even if assembling a brain or nervous system in such a way that the being is immediately in pain were possible, neither the brain nor the nervous system would exhibit the behavioral criteria for ascribing pain to a creature. The living animal might, but that is a further fact. And the nervous tissue we put together can certainly not being called "pieces of pains". That's nonsense.

To me, this question of whether pains are identical with brain states is similar to asking if flight is identical with engine states. Perhaps you couldn't have one without the other, but the question is still conceptually muddled beyond comprehension.

Also, I have to object to statements like "we see our own pain by internal observation". We cannot see inside our bodies, and we wouldn't find "pains" there if we could. We feel pains on our sensitive bodies, and we can say when we are in pain, but that doesn't require us to "see" or or to know by introspection. It is not a matter of knowing or perceiving.

Alexander R Pruss said...

I do not think that the difference between substances and states is relevant to this argument. I could have--and perhaps should have--replaced the substance water/H2O example with a state example like heat / molecular-motion.

Flight is not a state of the engine, but it is a state of the airplane.

Michael Gonzalez said...

Is flight a "physical state"? And is it a state of the airplane, in the same sense that the Physicalist is supposed to take pain to be a "physical state of" something?