The mind-body problem divides into several interconnected subproblems. One concerns the relation of consciousness to its material substratum in the brain and central nervous system. A second concerns the aboutness or intentionality of (some) conscious states. A third problem is how a physical organism can be subject to the norms of rationality: How does an abstract argument-pattern such as Modus Tollens 'find purchase in' and 'govern' the transitions from one brain state to another? A fourth subproblem has to do with mental causation. Obviously, mental states are causally efficacious in bringing about physical states and other mental states. My desire for another cup of java is part of the causal chain that eventuates in the physical process of ingesting caffeine. Note also that knowledge of the physical world would presumably not be possible unless physical states could enter into the etiology of mental states. (I say 'presumably' because my formulation begs the question against idealism. And don't let anyone tell you that idealism is not a live option! The fact that it is not much discussed these days doesn't mean anything. Academic philosophers can be as fashion-conscious as teenage girls, and as worried about how they appear; idealism is currently not discussed in the more fashionable salons.)
Divide and conquer is one approach to any complex problem: separate out the subproblems and try to solve them separately. For example, separate the 'qualia' problem — which is part of the first subproblem mentioned — from the intentionality problem.
It might be that there is nothing specifically mental about intentionality at all. Perhaps intentionality is to be found in nature and in artifacts below the level of mind. If so, it may be possible to understand intentionality at the level of mind by working up to it 'from below.' It may be possible to build a 'gradualist bridge' from mindless intentionality to minded intentionality. One might then come to understand how intentionality in us has 'evolved.'
Now one very serious question is whether intentionality can be prised apart from consciousness and treated separately. This is a question Colin McGinn raises with great skill. It deserves a separate post. In this post, however, I will examine a passage from Daniel Dennett in which our man, having separated the qualia and intentionality problems, tries to get from mindless intentionality to the minded variety. The passage is from Kinds of Mind, p. 35:
Intentionality in the philosophical sense is just aboutness. [. . .] A lock and key exhibit the crudest form of intentionality; so do the opioid receptors in brain cells — receptors that are designed to accept the endorphin molecules that nature has been providing in brains for millions of years. [. . .] This lock-and-key variety of crude aboutness is the basic design element out of which nature has fashioned the fancier sorts of subsystems that may more deservedly be called representation systems, so we will have to to analyze the aboutness of these representations in terms of the (quasi?) aboutness of locks-and-keys in any case.
If I am thinking about Jude Acers, my thought is about him: he is not about my thinking. Generalizing, we can say that intentionality is an asymmetrical relation: if X stands in the intentional relation to Y, then Y does not stand in the intentional relation to X. (Brentano rightly pointed out long ago that intentionality is not a relation, strictly speaking, but ein Relativliches, something relation-like; but this nuance does not harm my point.)
Now in Dennett's example, is the lock about the key or the key about the lock? Well, there is a sense in which each is about the other. By studying the key, I can infer something about the lock, and by studying the lock I can infer something about the key. Each provides information about the other, and to a locksmith, a great deal of information.
There are many cases like this. Animal droppings on the trail provide information about what manner of critter has been by recently. Bear scat 'means' bears have been around. One sort of footprint 'indicates' that a coyote has passed by, another sort a mountain lion. The paw of a coyote provides information about the type of print it would leave if it were to leave a print, and a footprint provides information about the design of the paw. (Here 'design' just means pattern.)
So in the coyote case as in the lock and key case we have symmetrical aboutness: lock is about key, and key about lock; paw is about footprint, print is about paw. Or consider a compass needle. It is about magnetic North in the sense that one can infer where magnetic North is from the direction in which the the needle is pointing. But equally, one can infer from the location of magnetic North where a properly functioning compass needle will point.
The symmetry of this sort of aboutness — call it aboutness1 — gives us excellent reason to distinguish it from intentionality, or aboutness2, which is asymmetrical.
From this one can see that Dennett is completely mistaken in his claim that lock-and-key aboutness is a "form of intentionality." It is not a form of intentionality, and to think that it is is to confuse the the two senses of 'aboutness' lately distinguished. Dennett himself seems to be aware of this since at the end of the passage quoted he shifts his ground and speaks of "quasi-aboutness." This fudge is very telling. No doubt there is some likeness as between lock-and-key aboutness and intentional aboutness, but that proves nothing since everything is like everything else in some respect.
The point is that one gains no insight at all into how intentionality emerges — if it does emerge — by having it compared with locks and keys. Note also that to infer something about the lock from the key presupposes genuine intentionality on the part of the locksmith.
To sum up. To build his gradualist bridge, Dennett looks for a form of primitive intentionality below the level of mind or consciousness. He thinks he has found it in his lock and key example. But what I have just shown is that the symmetrical aboutness in the lock and key case is not, and cannot be, a form or type or species of intentionality — which is asymmetrical. The former merely resembles the genuine article. But if A resembles B, it does not follow that A is a form of B. A decoy duck resembles a duck but is not type of duck.