I outline a dilemma for Derek Parfit’s project to vindicate moral realism. In On What Matters, Parfit argues that the best versions of three of the main moral traditions agree on a set of moral principles, which should make us more confident about the prospects of truth in ethics. I show that the result of this Convergence Argument can be interpreted in two ways. Either there remain three separate and deontically equivalent theories or there remains just one theory, the Triple (...) Theory. Both interpretations fail to deliver what Parfit is looking for. The first interpretation leads to a situation of underdetermination of theory choice that gives rise to a skeptical challenge. The second interpretation jettisons Parfit’s Conciliatory Project, that is, the reconciliation of the three moral traditions. The dilemma, I contend, is the result of Parfit failing to resolve two antithetical lines of thought. His search for the Trinity of moral theorizing must thus fail. (shrink)

In this paper, I introduce a new challenge to moral realism: the skeptical argument from moral underdetermination. The challenge arises as a consequence of two recent projects in normative ethics. Both Parfit and a group called consequentializers have independently claimed that the main traditions of normative theories can agree on the set of correct particular deontic verdicts. Nonetheless, as Dietrich and List :421–479, 2017) and myself :191–221, 2018; Australas J Philos 97:511–527, 2019; Ethical Theory Moral Pract 24:999–1018, 2021a) have argued, (...) the traditions still disagree about why these are the correct verdicts. This means that we can understand the situation in terms of an idea from the philosophy of science, the underdetermination of theory by the evidence. Yet underdetermination figures in one of the most important skeptical challenges to scientific realism. I show how an analogous skeptical argument can be construed for the moral realm. I propose a standard form for that argument. I then defend it against three possible objections, arguing that it is at least as plausible as, if not more plausible than, its counterpart in the philosophy of science. (shrink)