Against Identity Theories

Against Identity Theories

Would it shock you to learn that so-called identity theories are not identity theories? If so, prepare to be shocked (I was). Proponents of these theories called them identity theories, but they were mistaken about their true import. This puts them in a new light. Consider the following statements: “water is H2O”, “heat is molecular motion”, “light is a stream of photons”, “gravity is curved spacetime”, “air is a collection of gases”, “genes are DNA molecules”, “colors are dispositions to produce color experiences”, “thought is inner speech”, “sensations are brain processes”. Suppose, for the sake of argument, that these statements are all true. The question is what do they say—their logical form, semantic analysis, conceptual content. The standard view is that they are identity statements like “Hesperus is Phosphorus”, “Clark Kent is Superman”, “lifts are elevators”, “I am Colin McGinn”, “Tuesday is the day before Wednesday”, “hombres are men”, etc. These can all be paraphrased by inserting “identical to” after “is” or “are”. They all have the logical form “A = B”. You can invert the flanking terms and preserve truth. They are typically a posteriori but can be a priori. They obey Leibniz’s law. They are not explanatory or explicative: they don’t purport to tell you the nature of anything. They are not theoretically interesting or speculative. The “is” in them is the “is” of identity not of predication or composition. They form the class of identity statements, expressing a distinctive type of proposition (this is identical to that). The question is whether the list of sentences I first mentioned belongs to this class: do they say, and say only, that this is identical to that? Let us first pay attention to a curious linguistic fact: we don’t usually invert the terms in the sentences in question. We don’t normally say “H2O is water” or “molecular motion is heat” or “inner speech is thought” or “brain processes are sensations” (when was the last time you heard somebody say “C-fiber firing is pain”?). It sounds a bit off, a bit point-missing; yet true identity statements permit it smoothly. The reason for this is not a mystery: such statements are intended to say that something already identified has a certain nature. You designate a specific stuff or kind and then say what its nature is—its essence, its underlying reality. You don’t say “the nature of H20 is water” or “the nature of brain processes is sensation”. These statements are asymmetrical specifications of nature or essence, not (merely) statements of symmetrical identity. The “is” is the “is” of explication, essence-specification. It is not logically required that the kind be identical to its essence; indeed, it sounds funny to say “water is identical to its essence H2O”. It hasthat essence but it isn’t that essence. Does the essence or nature of water come out of taps or form lakes? We have discovered the nature of a certain kind of thing and we give voice to such discoveries by enunciating sentences of this form; we are not merely announcing a discovery of simple identity. We aren’t reporting that two modes of presentation converge; we are saying what the nature of something is. Even if the proposition in question entails a correlated identity proposition (which I doubt), the main point of the statement is to say something not merely informative but explicative—illuminating, penetrating. The chemist or physicist is not just assembling a list of brute identities but a series of substantive theoretical discoveries. We should therefore not describe these as “theoretical identities” but “theoretical explications”. The scientist is not saying anything like “water is aqua” or “heat is thermal” or “thought is cognition” or “pain is suffering”. Nor is it a mere matter of a posteriori discovery like Hesperus and Phosphorus: we could have two names for heat that have different senses, thus allowing for an a posteriori statement, but that is not the same as discovering the essence of heat by scientific investigation (using a microscope etc.). I suggest giving up labeling the discoveries in question “theoretical identities” and replacing it with “theoretical explications”; it aids clarity. The statements in question really mean “the nature of X is Y”, as in “the nature of water is H2O”.

Why does it matter? First, it is quite wrong to say that brain scientists have discovered an identity between mind and brain; they have discovered a correlation which philosophers claim to be an identity. It isn’t at all like discovering that Hesperus is Phosphorus or Clark Kent is Superman, in which you can trace the object through space and time and observe its different appearances. But second, and more important, once we see what the claim really is its plausibility tends quickly to evaporate. Suppose I assert “the nature of pain is C-fiber firing”: that bold claim is apt to be met with a resounding “No, it’s not!”. There is something mumbo-jumbo-ish about “pain is identical to C-fiber firing” (only a philosopher would say it), whereas “the nature of pain is C-fiber firing” is creditably straightforward—there is no hanky-panky going on. We know just what is being claimed, and it is not remotely symmetrical (“the nature of C-fiber firing is pain”). In the case of water and heat such statements are clearly true, but in the case of pain this is not so—we have been given no cogent reason to accept that the nature of pain is C-fiber firing. Is the nature of thought neural activity in the pre-frontal cortex? Is that its real essence? Hardly. The so-called identity theorist needs to put his cards on the table so that we can see what he has, and when he does his hand looks decidedly weak. We know what he wants to say—what a genuine materialist believes—but he cloaks it in talk of “theoretical identities” based on misdescriptions of what goes on in science. He derives spurious support from this sketchy maneuver. Better to come right out with it in plain language—“sensations have a neurological essence” or “thoughts have an axon-dendrite nature”. Then at least we know what exactly is being claimed. And we are apt to respond with incredulity, since we intuitively suppose that pain’s essence is a certain type of feeling (and we definitely don’t naturally take to the idea that feelings have a molecular nature). When the position is stated in terms of identity, we easily fall into the picture of two modes of presentation of the same thing, but that model does not work in the present case (since the appearance of pain is pain). So-called identity theorists have traded on these confusions for a long time; they would serve us better by owning up to the actual content of their doctrine, viz. that consciousness and all its contents have a bodily-physical essence involving biological cells. That sounds preposterous to most people, while the corresponding claims about water, heat, gravity, color, thought and inner speech, etc. seem eminently reasonable. The truth is that there is no such thing as the identity theory: that is a misnomer for something else entirely, i.e., a claim about essence or nature. By all means carry on saying “heat is molecular motion”, but don’t gloss this as “heat is (strictly) identical to molecular motion” while thinking the while about the model of “Hesperus is identical to Phosphorus”.[1]

[1] If I were to make a list of all the types of “is” I would say: the “is” of predication, the “is” of identity, the “is” of composition, the “is” of essence or nature, and the “is” of definition (there may be others). Part of the problem has been that philosophers have only thought about the “is” of predication and the “is” of identity (sometimes adding the “is” of composition); but sometimes we use this little word to convey what we have impressively discovered (or think we have) about something. If anything, this is the “is” of predication. And it is really not plausible that we have discovered materialism to be true of the mind, as we have discovered atomism to be true of matter. It’s a philosophical theory not a scientific fact.