 (CA) faces serious problems, especially as a sufficient condition for ability, even once we set to one side contentious claims about freedom and determinism. If this is correct, then (CA) must either be modified or rejected outright. Let us first consider the prospects for modification.
The guiding idea of hypothetical accounts is that abilities are to be defined in terms of what someone would do were he in certain psychological conditions. There are a number of ways of developing this idea that do not fit into the form of (CA). At least two such proposals deserve attention here.
Donald Davidson takes concerns about the sufficiency of (CA), especially as developed in Chisholm 1964, to tell decisively against it. More specifically, he takes the lesson of this problem to be is that:
The antecedent of a causal conditional that attempts to analyze ‘can’ or ‘could’ or ‘free to’ must not contain, as its dominant verb, a verb of action, or any verb which makes sense of the question, Can someone do it? (Davidson 1980, 68)
Davidson suggests that we may overcome this difficulty at least by endorsing:
A can do x intentionally (under the description d) means that if A has desires and beliefs that rationalize x (under d), then A does x. (Davidson 1980, 68)
Davidson proceeds to consider a number of further problems for this proposal and for the causal theory of action generally, but he takes it to suffice at least to overcome standard objections to the sufficiency of (CA).
The trouble is that it is not at all clear it does so. For these objections did not essentially depend on a verb of action figuring in the antecedent of the analyzing conditional. Consider Lehrer’s case again. It seems true that if Lehrer’s imagined agent has desires and beliefs that rationalized that action under the description ‘eating a red candy’—namely, adopting the analysis of Davidson 1963, a desire for a red candy and a belief that this action is a way of eating a red candy—she would eat a red candy. But the trouble is precisely that, in virtue of her 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 clos