ects. Abilities are properties of agents, rather than of things that are not agents. Objects have dispositions and affordances — as a glass is disposed to break when struck, or affords the drinking of liquid — but they do not have abilities. Being a power of an agent is not, however, a sufficient condition for being an ability. This is because agents have powers that are not abilities. Therefore, second, abilities need to be distinguished by their objects: abilities relate agents to actions.
Some examples may make the need for this second condition clear. Some powers, though properties of agents, do not intuitively involve any relation to action. Consider the power of understanding language. Understanding a sentence, while it is not wholly passive or arational, is not typically an action. In contrast, speaking a sentence is. Thus the power to understand French will not be an ability, on the present taxonomy. In contrast the power to speak French will be an ability, since it involves a relation to action. (See van Inwagen 1983, 8–13.)
So, as the term will be understood here, an ability is a power that relates an agent to an action. This way of demarcating abilities, while serviceable for our purposes, is not unproblematic. For it inherits the problems involved in drawing the distinction between actions and non-actions. First, there is the problem that the domain of action is itself a contentious matter. Second, there is the problem that, even if we have settled on an account of action, it is plausible that the domain of action will be vague, so that there are some events that are not definitely actions, but that are not definitely not actions either. Arguably both of these points about action apply, also, to the property of being an agent. If this is right, then the present account of ability, which is cashed out in terms of agency and action, will be correspondingly contentious and vague. Borderline cases may, in the end, generate problems for the theory of ability. But such problems will not be central here. For giving such a theory will be difficult enough even when we focus on paradigm cases of agency and action, and so on paradigm cases of ability.
Note there is a similarity between the present category of ability, as distinct from other powers, and the traditional category of active powers, where active powers are those that essentially involve the will (Reid 1788/2000). But it is not clear that these distinctions overlap exactly. For example, the power to will itself will clearly be an active power. It is less clear whether it will count as an ability, for the answer to that question will turn on the contentious question of whether willing is itself an action.
Some will expect that an account of ability would also be an account of what it is to know how to perform an action, on the supposition that one knows how to perform a certain action just in case one has the ability to perform that action. This supposition, which we may call the Rylean account of know how (since it is most explicitly defended in Ryle 1949, 25–61), has been called into question by Jason Stanley and Timothy Williamson (Stanley and Williamson 2001). Let us briefly consider Stanley and Williamson’s argument and how it bears on the theory of ability.
Stanley and Williamson argue, on broadly linguistic grounds, that our default view of know how ought to be rather different from Ryle’s. Part of the argument for this is that standard treatments of embedded questions (‘know who’, ‘know where’, and so forth; see Karttunen 1977) suggest a rather different treatment. On this treatment, to know how to A is to know a certain proposition. At first pass, in Stanley and Williamson’s presentation, for S to know how to A is for S to know, of some contextually relevant way of acting w, that w is a way for S to A. Stanley and Williamson develop and defend such a treatment, and offer independent considerations for rejecting Ryle’s own arguments for the Rylean view. On their view, then, to know how to A is not to have an ability.
Stanley and Williamson’s arguments 