An article by Alex Voorhoeve and me called ‘Why It Matters That Some Are Worse Off Than Others: An Argument against the Priority View’  (Philosophy & Public Affairs) includes a link to this post ‘for remarks by Derek Parfit in reply to this article, plus the authors’ response’. Parfit’s reply, ‘Another Defence of the Priority View’ , has been published in this special issue of Utilitas  on prioritarianism. I’ve now just published an article called ‘Prioritarianism and the Measure of Utility’  (Journal of Political Philosophy) that responds to Parfit’s. Here’s an excerpt that conveys the gist of my article:
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’. …I shall argue that prioritarianism cannot be assessed in such abstraction from an account of the measure of utility. Rather, the soundness of this view crucially depends on what counts as a greater, lesser, or equal increase in a person’s utility. In particular, prioritarianism cannot accommodate a normatively compelling measure of utility that is captured by the axioms of John von Neumann and Oskar Morgenstern’s expected utility theory. Nor can it accommodate a plausible and elegant generalization of this theory that has been offered in response to challenges to von Neumann and Morgenstern. This is, I think, a theoretically interesting and unexpected source of difficulty for prioritarianism, which I shall explore in the remainder of this article.