The standard philosophical model of intentional action-explanation appeals to states of belief and desire to do the explaining. This chapter evaluates what philosophers have had to say about the nature of desire. Chapter 5 showed that the ordinary notion of desire encompasses two very different kinds of mental state: goals and intentions, on the one hand, and affective or emotion-like forms of desire, on the other. The focus here is on the latter. The chapter shows that desires of this sort always incorporate anticipatory pleasure, and that pleasure itself is an analog-magnitude representation of value. The chapter begins with what the science can tell us about the respective natures of pleasure and desire, before comparing the results with claims made by armchair-philosophers. Many of the latter are false, albeit sometimes containing partial insights.