Moral underdetermination and a new skeptical challenge

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 (On what matters, vol 1. Oxford University Press, Oxford, 2011a) 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 (Philos Rev 126(4):421–479, 2017) and myself (Baumann in J Ethics Soc Philos 13(3):191–221, 2018; Australas J Philos 97(3):511–527, 2019; Ethical Theory Moral Pract 24(4):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.