er psychological disability, she is incapable of having this desire, and so cannot perform this action intentionally. For this reason it does not seem that Davidson’s proposal successfully overcomes the sufficiency problem, at least not on Lehrer’s way of developing that problem.
A second and rather different approach to modifying (CA) has been taken in recent work by Christopher Peacocke. Peacocke accepts that (CA) is insufficient in light of counterexamples like Lehrer’s. But he argues that we might supplement (CA) in order to overcome these difficulties. In the terms of the present discussion, Peacocke’s proposal is: S has the ability to A just in case: (i) (CA) is true of S and (ii) the possibility in which S tries to A is a ‘close’ one. The closeness of a possibility as it figures in (ii) is to be understood, at first pass, in terms of what we can reasonably rely on: a possibility is a distant one just in case we can reasonably rely on it not obtaining; otherwise it is a close one (Peacocke 1999, 310). To modify one of Peacocke’s examples, the possibility of toxic fumes being released into a train car that is safely insulated is a distant one; on the other hand, the possibility of toxic fumes being released into a train car where they just happen to be blocked by a fortuitous arrangement of luggage is a close one.
Peacocke’s thought is that this suffices to overcome the sufficiency objection: though Lehrer’s agent satisfies (i), she does not satisfy (ii): given the facts about his psychology, the possibility that he tries to A is not a close one. The trouble, however, is that Peacocke’s proposal is subject to modified versions of Lehrer’s counterexample. Consider an agent whose aversion to red candies is not a permanent feature of her psychology, but an unpredictable and temporary ‘mood’. Consider the agent at some time when she is in her aversive mood. This agent satisfies (i), for the same reason as above, and she also satisfies (ii): given the fragility of her mood, the possibility of her trying is a close one in the relevant sense. Yet such an agent lacks the ability to eat a red candy, in precisely the same way as she does in Lehrer’s original example.
It is an interesting question how we might develop other ‘supplementation’ strategies for (CA) (such strategies are also suggested by Ginet 1980), though the track record of this method of analysis in other domains (for instance, the project of ‘supplementing’ the analysis of knowledge in terms of justified true belief, in response to (Gettier 1963)) does not inspire confidence.
There is a surprising disconnect between the way abilities have been discussed in the philosophical literature in the tradition of Hume and the way that they have been approached in more recent work in logic and linguistics. Here, ability claims are understood as categorical possibility claims: claims about what some agent does in some non-actual state of affairs (or ‘possible world’). Let a modal theory of ability be any theory on which claims about an agent’s abilities are understood in terms of claims about what that agent in fact does at some possible world (or set of worlds). The idea that some such modal theory of ability must be true is a presumption of much formal work on ability and ability-ascriptions. Yet there are serious challenges to the idea that ability is in this sense a modality.
Intuitively, claims about ability are claims about possibility. It is in some sense a truism that someone is able to perform some act just in case it is possible for her to perform it.
To develop this purported truism, begin with the thought that for S to have an ability to A it is necessary, but not sufficient, that it be possible that S does A. This claim will be contentious for various more specialized sorts of possibility, such as nomic possibility. But if we may help ourselves to the idea of possibility simpliciter (‘metaphysical possibility,’ on at least one reading of that phrase), then this claim appears plausible. (We will survey some historical and contemporary challenges to it below i