Desire, preference, and utilitarianism

Desire-satisfaction utilitarianism (DSU) holds that the right thing to do is what maximizes everyone’s total desire satisfaction.

This requires a view of desire on which desire does not supervene on preferences as in decision theory.

There are two reasons. First, it is essential for DSU that there be a well-defined zero point for desire satisfaction, as according to DSU it’s good to add to the population people whose desire satisfaction is positive and bad to add people whose desire-satisfaction is negative. Preferences are always relative. Adding some fixed amount to all of a person’s utilities will not change their preferences, but can change which states have positive utility and which have negative utility, and hence can change whether the person’s on-the-whole state of desire satisfaction is positive or negative.

Second, preferences cannot be compared across agents, but desires can. Suppose there are only two states, eating brownie and eating ice cream (one can’t have both), and you and I both prefer brownie. In terms of preference comparisons, there is nothing more to be said. Given any mixed pair of options i = 1, 2 with probability p_i of brownie and 1 − p_i of ice cream, I prefer option i to option j if and only if p_i > p_j, and the same is true for you. But this does not capture the possibility that I may prefer brownie by a lot and you only by a little. Without capturing this possibility, the preference data is insufficient for utilitarian decisions (if I prefer brownie by a lot, and you by a little, and there is one brownie and one serving of ice cream, I should get the brownie and you should get the ice cream on a utilitarian calculus).

The technical point here is that preferences are affine-invariant, but desires are not.

But now it is preferences that are captured behavioristically—you prefer A over B provided you choose A over B. The extra information in desires is not captured behavioristically. Instead, it seems, it requires some kind of “mental intensity of desire”.

And while there is reason to think that the preferences of rational agents at least can be captured numerically—the von Neumann–Morgenstern Representation Theorem suggests this—it seems dubious to think that mental intensities of desire can be captured numerically. But they need to be so captured for DSU have a hope of success.

The same point holds for desire-satisfaction egoism.