[By Neil Sinhababu]
My last post was about what desire isn't, necessarily. (Namely, a representational capacity contributing to a reward or punishment signal.) Now I'm going to tell you what necessarily is. I've got a conceptual analysis that offers two conditions on something's being a desire, individually necessary and jointly sufficient. Here goes:
1> If someone desires B, and she occurrently believes that doing some action A can bring about B, she will do A.
2> If someone desires B, at least one of the following four relations between her beliefs regarding B and her hedonic state holds:
a. Increases in the subjective probability of B will cause her some pleasure.
b. Decreases in the subjective probability of B will cause her some displeasure.
c. Vividly imagining B coming about will cause her some pleasure.
d. Vividly imagining a state of affairs incompatible with B will cause her some displeasure.
So that's the analysis. The necessity of 2 is more controversial than the necessity of 1, so let me offer the case that inspires me to include it. It's a case I blogged about some time back:
On another planet, there exist the Neutrals -- intelligent creatures who are exactly like us, except that they are psychologically incapable of ever experiencing pleasure or displeasure. They engage in many motions similar to ours. Like a human, a Neutral would move quickly and suddenly towards his baby if he saw that the baby was about to crawl into a busy street. But while a human father might have an unpleasant experience of fear just as he began to move, a Neutral would not. Though the Neutral's attention would be intensely focused on the baby as he began to move and he would have lots of visual and auditory sensations, he would feel nothing unpleasant at all. Even if, in the future, he imagined what could've happened if he hadn't seen the child in time, he wouldn't feel the unpleasantness of horror in imagining. To an observer, Neutrals are indistinguishable from normal human beings. When you do things to one of them that would make a person laugh or cry, they show the outward behaviors of laughter and crying. But they don't feel the pleasure of laughter or the pain of sadness that we usually do when crying.
There are two questions I like to ask after giving this example: First, do any of the Neutrals' motions count as actions? (This becomes important for assessing questions about the relation between desire and motivation.) Second, (and more importantly for the topic of this post) do any of the Neutrals' mental states count as desires? I'd say that the Neutrals act, but the states motivating them aren't desires. Certainly, the Neutrals have some conative mental state. But I don't want to call this mental state a desire, since desire has to feel a certain way, and this way involves feelings of pleasure and displeasure. There's disagreement on this question, though (see the linked comments). Perhaps the word "desire" expresses two concepts -- one that applies to any old conative state, and one that only applies to states with a certain affective character. In that case, it's the latter concept that I'm analyzing.