What role do desires play in free will?
There have been many accounts of free will in terms of desires, from the basic Humean account to more sophisticated accounts from Frankfurt and Watson. However, none seem satisfactory because of important questions they leave unanswered and because of counter-examples which can be raised against them. It is because of this that, at least on these accounts, there is not a good enough justification for the claim that desires play a critical role in free will.
Frankfurt (Free Will ed. Gary Watson 1982, 81-95) proposed a theory that our freedom comes from our enjoyment of our second order desires. A first order desire is simply a 'want,' -- the desire for food, for example. It can come in many forms: it can be a desire of which we are unaware, which we do not wish to have, which we are apathetic to, and so on. It can either be one of many desires and not play the main role in what a person does, or it can be the sole motivating force in what a person does. Frankfurt defines the will as a desire which motivates the agent to act upon that desire: if I desire to eat a cream cake and, because of that desire I am motivated to eat a cream cake then my will, in Frankfurt's definition, is identical with that desire, that is, my will is to eat a cream cake. Second order desires are those desires we have which concern our first-order desire: we can desire to desire. For example, though I may desire a cream cake I may not desire to desire a cream cake; likewise, though I may not desire to work, I may desire to desire to work. In general, second-order desires entail first order desires: if I desire to desire to work, then that generally entails I have a desire to work, even if I do not work; this desire may simply be outweighed by other desires, like the desire to stay in bed; it is unlikely that I could desire to desire to work, but still have absolutely zero desire to work. It is possible, however, to desire to desire something, but also to wish that that desire is not satisfied. Frankfurt gives the example of a doctor who wishes to experience what it is like for a drug addict to crave a drug, yet at the same time does not wish that craving to be satisfied: he does not wish to actually get the drug (1982, 84-5). At heart, Frankfurt's theory is that we enjoy freedom of the will if our motivating first-order desires, i.e. our will, are in conjunction with our second-order desires. So, for example, a man who desired not to desire cream cakes but yet still kept eating them would not be enjoying freedom of the will in this circumstance: he is bound by desires he does not wish to have.