Chapter 6 turns to metaethics and explains how the results in normative ethics might lead to a skeptical challenge. I start by revisiting Duhem and Quine and how they thought underdetermination should impact our view of science. I then explain why I understand the major challenge that moral underdetermination poses to be an epistemological, not a semantic, one. This leads me to sketch out the general lines of a skeptical argument to the effect that we should withhold belief in the explanatory claims of moral theories. I propose a standard form of the skeptical argument in science and show how it can be adapted to ethics.Finishing up, I address two possible objections. The first concerns the question of whether so-called theoretical virtues might tip the ballance between two deontically equivalent theories. The second questions whether withholding of belief is indeed the correct reaction to equally believable moral theories. Iargue that the skeptical argument in ethics is at least as plausible as, if not more plausible than, its counterpart in the philosophy of science.