Prioritarianism and the Measure of Utility

H ERE I present a challenge to prioritarianism, which is, in Derek Parfit's words, the view that 'we have stronger reasons to benefit people the worse off these people are'. 1 We have such reasons, according to this view, simply by virtue of the fact that a person's 'utility has diminishing marginal moral importance' 2 -i.e., that equal improvements in a person's well-being matter less, morally speaking, the better off she is in absolute terms.It follows, from this view, that one might have stronger reason to benefit someone who is less well off rather than someone who is better off, even when this benefit would amount to a lesser increase in utility than a benefit to the better off person.3 In discussions of prioritarianism, it is often left unspecified what constitutes a greater, lesser, or equal improvement in a person's utility.In his own defence of prioritarianism, for example, Parfit explicitly prescinds from 'difficult questions . . .about what it would be for some benefits to be greater than others' and 'simply assume[s] that we can distinguish between the size of different possible benefits'.4 Parfit just stipulates numerical benefits of different magnitudes that