On Materialism and Qualia: The Explanatory Gap, by Joseph Levine
1. “When we imagine a possible world in which a phenomenon is experienced as pain but we have no C-fibers, that is a possible world in which there is pain without there being any C-fibers. This is so, argues Kripke, for the simple reason that the experience of pain, the sensation of pain, counts as pain itself. We cannot make the distinction here, as we can with heat, between the way it appears to us and the phenomenon itself.”
2. Here Levine is referring to the difference between statement (1), “Pain is the firing of C-fibers” and statement (2), “Heat is the motion of molecules.” There is a certain way of conceiving of heat that is purely empirical; it is that phenomenon in the world which causes certain events (expansion and excitation of molecular clouds, boiling of water, &c.), on the one hand. On the other hand, heat feels to us in a certain way. There is, however, a way of explaining away the difference between what heat is and how it feels to us, by virtue of the fact that heat or its lack causes sensations in our physical bodies in a certain, predictable way—indeed, in the same way that it causes expansions of gases, and so forth. This is not the case with (1): that we could explain pain in terms of the firing of C-fibers tells us nothing about the subjective experience of pain as such, and because we can imagine a possible world in which the firing of C-fibers is not necessary for pain to exist, pain itself can exist apart from C-fibers. The differentiation between the sensation we call pain, and pain itself, is null: when we have begun talking about the one, we necessarily talk about the other. For this reason, there is an explanatory gap between the materialist way of explaining consciousness and the way in which we subjectively experience pain. Statement (1) seems contingent to us intuitively, whereas one can be disabused of the notion that (2) is contingent by explaining that the same thing that is explained by the motion of molecules is that which causes the sensation of heat to us.
3. Levine’s starting point in this article is Kripke’s argument that, firstly, all statements of identity in which both sides are true are necessarily true in all possible worlds; and secondly, that since a world can be conceived of in which statements of physical activity and psychological activity (viz., consciousness) are different, we must deny the materialistic necessity that psychological activity is reduceable to physical claims. Levine thinks that Kripke’s argument does not so strongly support a metaphysical claim as to the nature of consciousness, but that it does present a troubling epistemological problem. For the sake of argument, Levine essentially accepts a materialistic premise for the nature of the mind, but says that there is an explanatory gap between objective, empirical statements about neurophysiology and how we conceive of and subjectively experience what those statements purport to describe. He goes on to explain that this is a problem not only for strictly physical materialists, but also for functionalists as well, citing Ned Block’s argument that it is conceivable that for statement (3), “To be in pain is to be in [functional] state F,” an organism or even an entire nation of people, could corporately realize state F without actually being in pain. That this is logically possible is, for Levine, a strike against the abstraction of functionalist descriptions; as is the hypothesis that two people could share identical functional states but experience different sensory qualia, the so-called “inverted spectrum” hypothesis. None of this, even the functional description of states, helps us to understand the way something feels subjectively. Indeed, even if we restrict “pain” to being that which is subjectively felt when there is that sort of experience as C-fibers firing, that “makes the way pain feels into a brute fact,” and doesn’t tell us anything about why pain actually feels the way it does. In answer to this problem, Levine suggests that it is only highly organized physical systems that exhibit this kind of ambiguity; nevertheless, since the human mind is one of those systems, that (1) could be metaphysically factual while remaining epistemologically inaccessible. In the addendum to the article, Levine merely reiterates the dichotomy between physical description and subjective experience.
