Hasker on the divide and conquer strategy
Typically in the philosophy of mind we hear that there are two kinds of problems for naturalists. One is to account for raw experience or raw feels. Given physicalism, can we have the sorts of experiences that we would ordinarily think we have. The other concerns our intentional states.
Now many philosophers have suggested that the latter problem is less of a serious problem for physicalism than the former problem. The argument from reason deals primarily with the latter problem, and so in some sense it might be thought to be superfluous in this sense: if physicalists can get around the problem of qualia, dealing with intentionality or reasoning should be pretty easy.
Steven Stoljar in the essay on Physicalism for the Stanford Encyclopedia of Philosophy puts it this way:
As with the knowledge argument, the issues surrounding Kripke's argument are very much wide open. But it is important to note that most philosophers don't consider the issues of intentionality as seriously as the issue of qualia when it comes to physicalism. In different vocabularies, for example, both Block (1995) and Chalmers (1996) distinguish between the intentional aspects of the mind or consciousness, and the phenomenal aspects or qualia, and suggest that it is really the latter that is the central issue. As Chalmers notes (1996; p. 24), echoing Chomsky's famous distinction, the intentionality issue is a problem, but the qualia issue is a mystery.
William Hasker, however, does not seem to see it quite this way. He writes:
A maneuver that has recently become somewhat popular needs to be taken account of here. Some philosophers have thought it plausible to accept a functionalist account specifically for intentional states, while conceding the "phenomenal properties" objection for qualia and giving some other account (e.g., token identity) for those states. Once again let us concede, for the sake of argument, that th functinoalisty can successfully identify intentional states in causal-functional terms. Even so, ther eare at least two reasons why this maneuver does not succeed in disposting of the materialist's problem with intentional states. For one thing, some intentional stattes do involve qualitative "feels"; being embarrassed about one's appearance is an example of such a stae. In general, emotional states involve both a particular qualitative feel and also an intentional reference to whatever it is that one is happy, sad, proud, indignant, or embarrassed about. For these particular states, the "divide and conquer"strategy can't succeed.
An even more fundamental problem, however, is encountered in the "aboutness"which is the very essence of an intentional state. There just is such a thing as thinking about something, worrying or hoping that something may happen, believing that so-and-so is the case, deciding on a certain course of action--and in such cases one ordinarily has a distinct, conscious awareness of the "intentional object" of one's mental state. This sort of mental state is utterly familiar to each one of us, and if anyone were to claim not to understand what is meant, such a claim would be entirely lacking in credibility. Furthermore, the claim that a person is in such an intentional state is clearly not equivalent, logically or conceptually, to any causal-functional description of the person. The causal-functional properties of the sate identified by functionalism can be completely described and explained in terms of the physical structure and behavior of the state in question and its relations to other physical states. There is simply no place in such a description for the "aboutness which is essential to intentional states as such. And so we can pose a question parallel to he one asked previously: Are these causal-functional states such that they essentially involve "aboutness"? If the do not involve "aboutness" then they just are not intentional states--once again, the subject has been changed. If they do, then a crucial, and logically essential, aspect of those states has been left unexplained; we still have no idea how "aboutness" is to be incorporated into a materialist world-view.