The differences Block attempts to capture with his putative distinction between P-consciousness and A-consciousness are more directly and perspicuously handled in terms of differences in richness of content and degree of influence. Block's critiques, based on his misbegotten distinction, evaporate on closer inspection.
Block amply demonstrates that there is ubiquitous confusion among researchers about consciousness, and he is right to locate a major source of the confusion in the spectrum of differences he attempts to tame with his purported distinction between P-consciousness and A-consciousness. That distinction may start out seeming quite intuitive. Indeed, Block relies heavily on appeals to our intuitions to hold it in place until he can get it properly defined and defended, but once that effort gets underway, he runs into a swarm of difficulties from which there is apparently no escape. I for one found it difficult to keep track of the tangle of objections and counterobjections, exemptions, caveats and promissory notes, and will be interested to see if other commentators can find their way into, and back out of, the maze Block has created.
There is an alternative, much more direct path which he ignores, perhaps because it is deeply counterintuitive at first blush: the varieties of consciousness he thinks he sees falling under P-consciousness and A-consciousness can all be accommodated under the two rough quantitative headings of richness of content and degree of influence. Some episodes of mental life have impoverished contents, while others are so rich in content--so full of information about the perceived world, for instance--that one has the sense that no practical description or catalogue could do justice to them. The latter--and they are the normal, everyday episodes of consciousness--Block would declare to be instances of P-consciousness because they are, shall we say, phenomenologically impressive. The former, such as actual (as opposed to imaginary) cases of blindsight, have such vanishingly little content that subjects standardly deny that they are conscious of any content at all, though forced-choice guessing famously demonstrates that there was some content at work there after all, capable of influencing some choices, but unable to serve as the cue or prompt for rational action. Can such simple differences of quantity, not quality, do justice to the variety of phenomena? Don't we need something altogether different--qualia (or their absence)--as well? I have said No, and have defended this claim at length (Dennett, 1991), but it was apparently too drastic a stroke for some readers to accept--or in the case of Block, to be recognized as a serious alternative to be dealt with at all. But now Block has done my theory a fine service: nothing could make my admittedly counterintuitive starting point easier to swallow than Block's involuntary demonstration of the pitfalls one must encounter if one turns one's back on it and tries to take his purported distinction seriously.
The main trouble with Block's attempt to motivate two independent dividing lines (where I would put differences in degree) is that in the normal run of things, his two kinds of consciousness run together, as he himself acknowledges several times. He cannot provide clear examples of A-consciousness without P-consciousness or P-consciousness without A-consciousness, and while he claims that both are "conceptually possible," it is unclear what this comes to. Moreover, if these two sorts of consciousness are conceptually independent, as Block insists, then he is not entitled to several claims he makes about P-consciousness. Consider, for instance, his discussion of the phenomenon in which the solution to a difficult problem suddenly comes to you without conscious thought. He surmises that the "high level reasoning processes" by which you solve such a problem are not P-conscious (in addition to not being A-conscious). How does he know this? How could he know this, or even deem this more probable than not? He notes--but is apparently not embarrassed by--a similar problem with his account of blindsight. "Note that the claim that P-consciousness is missing in blindsight is just an assumption. I decided to take the blindsight patient's word for his lack of P-consciousness of stimuli in the blind field." (ms, p.27-8) But taking the subject's word is using the best criterion for A-consciousness as one's sole evidence of P-consciousness. Block himself demonstrates thereby that the very idea of a sort of consciousness independent of access is incoherent.
Although Block discusses my theory of consciousness at some length, his discussion always leans on the presupposition that his putative distinction is in place. My theory of consciousness is stranded, he concludes, between being trivially false (if a theory of P-consciousness), non-trivially false (if a theory of "just" A-consciousness) and banal if a theory of "a highly sophisticated version of self-consciousness." (ms. p22) But since I not only decline to draw any such distinction, but argue at length against any such distinction, Block's critique is simply question-begging. I may be wrong to deny the distinction, but this could not be shown by proclaiming the distinction, ignoring the grounds I have given for denying it, and then showing what a hash can then be made of ideas I have expressed in other terms, with other presuppositions. If Block thinks his distinction is too obvious to need further defense, he has missed the whole point of my radical alternative. This is a fundamental weakness in the strategy Block employs, and it vitiates his discoveries of "fallacies" in the thinking of other theorists as well. Those of us who are not impressed by his candidate distinction are free to run the implication in the other direction: since our reasoning is not fallacious after all, his distinction must be bogus.
What would a good test of the two different starting points be? Look at their treatment of a particular phenomenon--e.g. blindsight--from a neutral point of view. In my own discussion of blindsight (1991, p.332-43), I argued that if a patient could be trained to treat blindsight stimuli as self-cuing or prompting, this would amount to restoring the patient's consciousness of events in the scotoma, the only remaining difference between such experience and normal vision being the relative poverty of the content of what could be gleaned from the scotoma. Relative poverty of content--not "absence of qualia" or lack of P-consciousness--was a non-optional hallmark of blindsight, I claimed. To drive the point home, I asked, counterfactually, what we would conclude if we encountered someone who claimed to suffer from blindsight of a strange high-content variety--correctly "guessing" not just the words written on a page placed in the putative scotoma, for instance, but their typeface and color, for instance. I claimed this would stretch our credulity beyond the limit; we would not and should not take somebody's word that they were "just guessing" in the absence of all consciousness (all P-consciousness, in Block's terms) in such a case. Block, interestingly, thinks otherwise. He does not refer to my discussion of blindsight, but coins the term "superblindsight" to discuss much the same sort of imaginary case, and supposes without argument that in such a case we would credit the patient: "The superblindsighter himself contrasts what it is like to know visually about an 'X' in his blind field and an 'X' in his sighted field. There is something it is like to experience the latter, but not the former." (p.12)
Now here we have a direct difference of implication between the two starting points--a useful point of contrast even if the cases are not likely to come up for empirical confirmation! But the issue is not yet joined if we imagine the case the way Block invites us to do, with the huge normal difference in richness of content between the sighted field and the scotoma or blind field. If our imaginary patient, like all actual blindsight patients yet studied, can identify the typeface, size, colors and textures of the sighted-field 'X' and its background, but can only identify that there is an 'X' (as opposed to an 'O') in the blind field, this would be a large difference in richness of content that would account, on my view, for the patient's willingness to draw the sort of contrast Block imagines the superblindsighter to draw: it is "like something" to detect the 'X' in the sighted field, and it isn't like anything to detect the 'X' in the blind field.
For Block to put his claim about blindsight in direct competition with my alternative, he must control for richness of content, which I claim is the only other important variable; he must stipulate--in whichever way he chooses--that the richness in content is the same in both fields. The patient can tell us no more about the 'X' in the sighted field than about the 'X' in the blind field--either because the former is bizarrely impoverished, or the latter is bizarrely rich. Take the latter case first: would you "take the subject's word," as Block says, that it wasn't like anything at all for him to come to know, swiftly and effortlessly, that there was a bright orange Times Roman italic 'X' about two inches high, on a blue-green background, with a pale gray smudge on the upper right arm, almost touching the intersection? (That's a sample of the sort of richness of content normally to be gleaned from the sighted field, after all.) I for one would wonder what sort of lexical amnesia or madness had overcome anybody who could gather that much information from a glance and yet deny having any conscious visual experience. Alternatively, if all our imaginary patient can tell us about the 'X' in the sighted field is just that it was an 'X', not an 'O,' I think most people would be baffled about what he could possibly mean by his insistence that nevertheless he had "P-consciousness" of the sighted field, but not of the blind field (in which he made the same discrimination).
Imaginary cases are of limited value in such theoretical explorations, but this time I think the flight of fancy nicely reveals how Block mis-locates the issues. It is not that we others are "conflating" two sorts of consciousness; it is that he is inflating differences in degree into imaginary differences in kind.
Dennett, 1991 (as in Target Article)