Mind/Brain Identity Theories and Rigidity

 RD stands for rigid designator

We now know, assuming Kripke is correct, that if RD1 = RD2 is true, then it is necessarily true. That is, we know true identity statements that have rigid designators on both sides of the identity are true no matter what. They are true in all possible worlds. They are true in all possible histories of our world. No matter how our world could be, such statements cannot be false. 

Example 1: Water = H2O. Both sides are RDs. Hence, if that statement is true it is true in all possible worlds. There is no way our world could be such that Water is not H20. Water just is H2O. Since, the term ‘water’ (as we use it here and now) picks out the same stuff in every possible circumstance, and since the term ‘H20’ (as we use it here and now) picks out the same stuff in all possible circumstances, if Water = H2O, then that statement is true in all possible circumstances. We might associate all sorts of things with water—it falls from the sky, fills rivers and lakes, is drinkable, etc—but those things are simply reference-focusers. They are used by us to help direct our attention to WATER. But they are not to be confused with WATER. There are possible circumstances in which nothing falls from the sky, fills rivers and lakes, and is drinkable. There are possible histories of our world in which the stuff that falls from the sky, fills rivers and lakes, and is drinkable is not WATER. Water need not have done any of those things. But since we discovered that water is in fact H2O, that the nature of water is H20, then it simply cannot exist without H2O. It could exist without a bunch of the features we use to pick it out, to fix our attention on it, but it could not exist without being H2O.

Example 2: Heat = Molecular Motion. Both sides are RDs. Hence, if that statement is true it is true in all possible worlds. There is no way our world could be such that Heat is not molecular motion. Heat just is molecular motion. Since, the term ‘heat’ (as we use it here and now) picks out the same phenomena in every possible circumstance, and since the term ‘molecular motion’ (as we use it here and now) picks out the same phenomena in all possible circumstances, if Heat = Molecular Motion, then that statement is true in all possible circumstances. We might associate all sorts of things with heat—it causes a certain sensation in us, it is loved by those from the desert, hated by those from cold climates, etc—but those things are simply reference-focusers. They are used by us to help direct our attention to HEAT. But they are not to be confused with HEAT. There are possible circumstances in which nothing causes that kind of sensation, etc. There are possible histories of our world in which the phenomena that causes that type of sensation is not HEAT. Heat need not have done that. But since we discovered that heat is in fact molecular motion, that the nature of heat is molecular motion, then it simply cannot exist without molecular motion. It could exist without a bunch of the features we use to pick it out, to fix our attention on it, but it could not exist without being molecular motion.

In the philosophy of mind (and the cog and neurosciences and related disciplines) a widespread theory is that mental states or events are identical with brains states or events. This theory is popular in part because the more global theory of materialism is popular, namely, that everything that exists is a material state or event. If S thinks that materialism is true in the global sense (everything is material), then S had better think that materialism is true with respect to mental events. There are varieties of materialist identity theories, but I am going to ignore them in this post. 

The term ‘pain’ appears to be an RD (focus on physical pain, but any kind of pain should work, so long as it really is a pain). It refers to the same event in every possible circumstance. If something does not have the feel of a pain, it is not a pain, and if something feels like a pain, then it is a pain. Hence, ‘pain’ is an RD. 

The term ‘C-fibers firing’ appears to be an RD (this is just a stand-in for whatever it is that scientists discover is the actual brain event that is correlated with pain). It refers to the same event is every possible circumstance. If something is a C-fiber but is not firing then it is not a C-fiber firing event, and if something is a C-fiber and is firing, then it is a C-fiber firing event.

Brief Detour: Suppose that ‘C-fiber firing’ is not an RD. That is, suppose that it is actually a disguised description. In this case ‘C-fiber firing’ is really just short for something like ‘the immediate cause of pain’ or ‘the thing that is identical to pain’ or … If this were true—if ‘C-fiber firing’ were just an abbreviated description, then the statement “Pain is C-fiber firing” would be just like the statement “Ben Franklin is the inventor of bifocals.” And just like that latter statement is not necessarily true, the former would not be either. In other words, just as it is possible for Ben Franklin to exist without ever having invented the bifocal, it is possible for pain to exist without being a C-fiber firing. So, on the assumption that ‘C-fiber firing’ is really a disguised description, the identity theory is false. So, Kripke’s claim that ‘C-fiber firing’ is an RD does not beg any questions against the identity theorist. Indeed, it makes his job harder for him. 

So, if the statement “Pain = C-fiber firing” expresses a truth, then it must be a necessary truth. That is, there is no possible world, no possible history of our world, where a pain occurs and C-fiber firing does not, and there is no possible world, no possible history of our world, where a C-fiber firing occurs and a pain does not. 

But, says Kripke, that just seems false. At the very least, it seems quite easy to imagine a circumstance in which I am in pain and there are no C-fibers firing or a circumstance in which C-fibers are firing and I am not in pain. 

Possible Circumstance 1: Imagine that the famous philosopher Bishop Berkeley is correct and there are no physical objects at all. The only things that exist are minds, their ideas, and God.  He thought that such a thing is actually true of our world. You probably do not. But it seems possible to imagine a world just like ours with all of the same appearances—things appear as trees, and dogs, and planets and molecules and etc—and the same feels and sensations but without there being any actual physical objects that underlie or correspond to those appearances and sensations. After all, it is both possible and sometimes actual that someone appears to see a tree without there being a tree, appears to hear a sound without there being a sound, etc—i.e. cases of perceptual hallucinations. If this is possible, then it is a world with pains but without C-fibers firing. Note that this does not at all require us to think that out world is like Berkeley thought it is. All it requires is that it is possible for our world to be like that. 

Possible Circumstance 2: Imagine that we get to a point where we can replace C-fibers with an artificial mechanism invented by us. Now imagine that such a thing fires. Would you experience pain? If so, then you would be in a pain-state and not in a C-fiber firing state. Note that the thing might be made at first of metal and electrical chips and later made of silicon and later made of something else entirely. In either case, it would be false to say that pain = C-fiber firing. Ah, but you say “but in all those cases we have pain = something x firing. So, the materialist theory is still true. Pain = material thing x firing.” Ok, but note that we have now abandoned the claim that mental events of type T are identical with brain events of type T for the claim that mental events of type T are identical with brain event of type T or T* or T** or… In such a scenario it is not even obvious that mental events are identical with brain events at all. For given the scenario it seems possible to replace the entire brain with something completely artificial. In that case, it is not at all obvious that what we would have is really a brain, because the term ‘BRAIN’ seems like an RD. So, in such a scenario as we are imagining, all we’d be saying is that mental events are correlated with some kind of material event but there is no type of material that is necessary for the mental event. So, we could have the exact same mental event—a pain, for example—and a completely different kind of material event, since the material could be completely different. This seems like a far cry from what the materialist is after, which is to reduce mental events to material events. For the following now seems possible on this scenario: I really could occupy the body of an alligator or a robot or … So, this might be compatible with the claim that I cannot exist without a body, it is also compatible with the claim that I (or my mental states) could be realized in a completely different body. This is not substance dualism (the claim that persons are souls and souls are completely separate substances from material substances and can exist without material substances) it is still a type of dualism. For now, mental events could possibly exist in coke machines J. 

Possible Circumstance 3: Suppose Jake has the following condition: he experiences pain just like you and I do, but his brain is wired quite differently than ours. His C-fibers do not fire at all. Is that possible? If so, then the identity theorist is in trouble. 

Possible Circumstance 4: Zombies. Yes, zombies have been part of the philosophical literature for thousands of years (though not always called that). A philosophical zombie is a being that has the same biochemical composition that you do but is completely lacking in mental states. In other words, while you have mental experiences—the taste of a lemon has a certain quality to it that is quite different from the taste of a banana, and the feeling of tranquility is quite different from the feeling of boredom, and a pain feels quite different from the feeling of an itch, etc—your biochemical twin zombie does not. All of the same material events occur in the body of the zombie but it’s completely dark inside. It is not even conscious. It’s just a zombie. If this is possible, then it is possible for C-fibers to fire without a feeling of pain. Now why think this is even possible. Well, we can imagine it, or at least we seem to be able to. And imagination is a decent, though not a foolproof guide to what is possible. True, some things are possible that we cannot imagine. But that is not relevant. 

Diagnosing a Mistake: At this point, you might be thinking that if all of that stuff above is possible then surely it is possible for heat not to be molecular motion and for water not to be H2O. But, says Kripke, what you are really doing is imagining a scenario where you have the sensation of heat without molecular motion or where stuff has the same look and feel and taste as water without being H2O. But those are not situations where heat is really something other than molecular motion and water is something other than H2O. What you are doing here is confusing the reference-fixing descriptions with the referent itself. Yes, Kripke says, we could be in a qualitatively identical situation—a situation where all of the same appearances occur to us—and there be no molecular motion and no H2O. But those are not a situation where there are heat and water, for heat just is molecular motion and water just is H2O. That’s what the science tells us and we are assuming just for the sake of argument that the science is correct. In other words, science has discovered the natures of water and heat. Those are H2O and molecular motion respectively. So, any situation without H2O is a situation without water and any situation without molecular motion is a situation without heat. But those situations—without H2O and without molecular motion—need not be situations without heat-like sensations or water-like appearances. 

But the same simply cannot be said for pain. A situation where you feel pain just is a pain-situation. This is what makes the claim that pain = C-fibers firing so difficult to sustain. You can have a heat-like sensation that is caused by something other than heat/molecular motion. But you cannot have a pain sensation without being in pain. They are one and the same, whereas a heat-sensation is not identical with heat itself, a pain sensation is identical with pain. 

So, Kripke says, the identity theorist is up a creek. At the very least she has her work cut out for her, and it looks like it’s going to be one hell of a pain J.