Without question, conscious experience (aka qualia, phenomenal experience, etc.) presents special problems of interpretation and explanation. On the one hand, we can't doubt that it exists (despite some philosophical quibbling over exactly what that's supposed to mean), nor does anyone seriously doubt that it's a characteristic of other human beings than oneself. Virtually all ordinary people (i.e., non-philosophers), in fact, also think it's a characteristic of a number of other animal species as well, but those same people are also likely to want to draw a line somewhere down the phylogenetic chain, and pretty certainly will wish to exclude things like rocks and machines from the class of conscious entities. So from a scientific (i.e., physicalist or naturalist) perspective, in other words, conscious experience appears to be an entirely natural phenomenon, that's evolved in certain organisms but not others, that's localized in time and space, and that's as subject to cause and effect as any other phenomenon. Yet on the other hand, out of all phenomena, and in a very odd sort of way, it seems to be alone in being inherently unobservable -- not unobservable because it's too small or too quick or too slow, in other words, but because it's not something that can be observed, even in principle. We can see the effects of the phenomenon, in the sense of the behavior it generates, and we can see something of the underlying mechanisms that themselves generate the phenomenon, but we can't see "seeing" itself ... or see "hearing", or "tasting", or "hurting", etc. Experience itself, in other words, can only be experienced, rather than observed, and each conscious entity can only experience its own experience.
Little wonder, then, that all attempts at an explanation of conscious experience have left at least an appearance of an "explanatory gap" -- as David Chalmers says, in his seminal paper on this topic:
... even when we have explained the performance of all the cognitive and behavioral functions in the vicinity of experience - perceptual discrimination, categorization, internal access, verbal report - there may still remain a further unanswered question: Why is the performance of these functions accompanied by experience? A simple explanation of the functions leaves this question open. [emphasis his]
This sense of a gap or inadequacy, that remains even after all attempts at explanation, is a persistent one, to an almost surprising extent, and in what follows I want to look at some of the reasons for that. A start would be to notice that not all gaps are explanatory gaps -- some "gaps" may be a sign not so much of a lack or absence but rather simply of a difference, in the same ordinary way, for example, that categories are different (failing to recognize such difference leading to the familiar notion of the "category mistake"). Here are some examples of simple differences that might appear, wrongly, as an "explanatory gap":
- There's a difference between an explanation of function -- which is an answer to the "why" question -- and an explanation of mechanism -- which answers the "how". In particular, it may be possible to answer why there is experience -- because experience just is the information necessary for behavior control, for example -- without, yet, being able to answer how there is experience.
- There's also a difference between any sort of explanation of a phenomenon and the phenomenon itself. This may seem obvious, and indeed it is in almost any other instance, but there often seems to be an element of this difference implicit in complaints along the lines of: "but that explanation still doesn't give us the experience of red, say", even if both the function and the mechanism of experience had been explained. Part of the problem may be that both explanation and experience are phenomena of consciousness, and we may have an expectation that the latter should be contained somehow in the former (partly at least for reasons given in the next point).
- And then there's a difference in perspective, between the view of a phenomenon from the outside, as it were, and the view from inside -- the view you get when you're not just a part of the phenomenon yourself, but when the "view" itself is the phenomenon. With this difference in perspective, of course, we're getting closer to the nub of the real problem here -- it's as though explanation, in the unique case of this particular phenomenon, is trying to wrap back on its own origins, and baffling itself with its own reflection.
Now, I don't expect any of this to dispel the appearance, at least, of an "explanatory gap", an appearance that has a very powerful grip on our intuitions. But what I hope these kinds of reflections might begin to suggest is that much of the philosophic problem of conscious experience is located not necessarily in the phenomenon itself but rather in the particular, and peculiar, nature of that "gap".
UPDATE: Here's the conclusion to this series [see "The 'explanatory gap' series: a summary and a Q and A" above].