  Those who interpret utilities in terms of personal preference face a special challenge: the so-called problem of interpersonal utility comparisons. When making decisions about how to distribute shared resources, we often want to know if our acts would make Alice better off than Bob—and if so, how much better off. But if utility is a measure of individual preference, there is no clear, meaningful way of making these comparisons. Alice's utilities are constituted by Alice's preferences, Bob's utilities are constituted by Bob's preferences, and there are no preferences spanning Alice and Bob. We can't assume that Alice's utility 10 is equivalent to Bob's utility 10, any more than we can assume that getting an A grade in differential equations is equivalent to getting an A grade in basket weaving.