Frankfurt on Freedom of the Will V
Let's make a final pass over this issue of reasons for action. Frankfurt thinks that the concept of a person is of beings "capable of wanting to be different, in their preferences and purposes, from what they are." But it is impossible to make sense of what would count as reasons for wanting to be different in that way. One might wish that some of one's desires, a small subset radically inconsistent with the vast majority of ones desires, would simply go away in order to liberate one from the irrationality of an inconsistent set of desires. Such is the wish of the unwilling drug addict, for example. But this wish is a desire generated by the set of first-order desires. In fact, it supervenes on them. It even supervenes logically, given a the simple recipe for prudential rationality I've proposed in the earlier posts. In other words, there is nothing to this wish other than the first-order desires themselves.
The picture Frankfurt offers, then, commits itself to externalism about reasons for action: that they are independent of one's first-order desires. This he does in order to rescue free will from obscurity. However, externalism is an inscrutable notion. No one has any idea of a reason to desire that is independent of one's antecedently held desires. Reason is, as Hume said, the slave of desire. Furthermore, as we've seen, the commitment to externalism is not necessary in order to explain free will.