In their discussions of action, many philosophers reject or ignore mental activity and consider only physical or bodily action. For example, Frankfurt writes, 'The problem of action is to explicate the contrast between . . . bodily movements that . .. [an agent] makes and those that occur without his making them.'1 Some philosophers discuss our control over beliefs by asking, as does Williams, whether we can believe at will in the way we can hold our breath at will.2 Other philosophers reject the very idea of intellectual activity. Here we might think of Ryle and the later Wittgenstein, and with perhaps more justice of their followers, who would seem to agree with Thalberg's claim that 'we would avoid gratuitous mysteries if we confine [the notions of] activity and passivity to the physical world'.3 These treatments of mental activity are inadequate. They are particularly strange coming from philosphers whose professional life is caught up in mental activity. Indeed, were there no mental activity, were people not active and responsible for what they think and believe, then what possibly and what in good conscience are we doing teaching, writing, discussing, and the like-in doing philosophy? But there is an attractive line of argument against the possibility of mental activity and responsibility. It can be presented by examining the philosophically typical cases of activity and responsibility. So it is asked what differentiates my arm's going up and my raising my arm, where the latter is a clear case of activity and responsibility, and the former is something else, perhaps something