Utilitarianism and prioritarianism make a strong assumption about measures of how good lotteries over histories are for individuals, or for short, individual goodness measures. Given some idealizing assumptions about interpersonal and intrapersonal comparisons, they presuppose that any individual goodness measure can be transformed into any other individual goodness measure by a positive affine transformation. But it is far from obvious that the presupposition is correct, so both theories face the threat of presupposition failure. The usual response to this problem starts by assuming that what implicitly determines the set of individual goodness measures is independent of our discourse about utilitarianism and prioritarianism. I suggest reversing this response. What determines the set of individual goodness measures just is the body of platitudes we accept about utilitarianism and prioritarianism. This approach vindicates the utilitarian and prioritarian presupposition. As a corollary, it shows that individual goodness measures are expectational, and provides an answer to an argument due to Broome that for different reasons to do with measurement, prioritarianism is more or less meaningless.
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