John J. Tilley

A common and plausible assumption about the relation between desires and practical reasons—namely, that if øing is an optimal way (or even just a way) for a person, P, to satisfy one of his or her desires, then P has a (normative) reason to ø. This paper discusses that assumption. Although it does not deny that desires are a source of practical reasons, it shows that in some situations, rare though not impossible, P can lack a reason to ø despite having a desire that he or she could satisfy optimally by øing.

In a recent issue of this journal, C. L. Sheng claims to havesolved andexplained the Prisoner's Dilemma (PD) by studying it ‘from a moral point of view’ - i.e., by assuming that each player feels sympathy for the other. Sheng does not fully clarify this claim, but there is textual evidence that his point is this: PD's arise only for agents who feel little or no sympathy for each other; they cannot arise in the presence of a high degree of reciprocal sympathy. A high degree of such sympathysolves the PD in that it prevents PD's from arising, and a low degree of itexplains the PD in that it provides an essential condition for the occurrence of that game. This thesis is false, as some examples show. These examples are important; they prevent us from underestimating the problem posed by the PD.

This thesis clarifies and defends the view of practical reason often dubbed "Humean", "instrumental", or "preference-based". Three familiar charges against this view are addressed, and claimed to be ineffective. They are: first, that the Humean view entails the easily refuted theory that all reasons for action have their source in individual desires; second, that it brings with it an extreme version of ethical relativism; and third, that it presupposes a view of motivation which has been shown to be false, or at least highly doubtful--the view, namely, that a desire is among the causal antecedents of any action. Against these charges I argue, first, that the Humean view does not entail that all reasons for action are desire-dependent; second, that it does not bring with it a version of moral relativism; and third, that although it does carry the implication that motivation has its source in desires, that implication is not threatened by standard arguments used against it.