At the intersection of meta-ethics and philosophy of science, Nicholas Sturgeon’s “Moral Explanation” ([1985] 1988), Richard Boyd’s “How to be a Moral Realist” (1988), and David Brink’s Moral Realism and the Foundations of Ethics (1989) inaugurated a sustained argument for the claim that moral kinds like right action and virtuous agent are scientifically investigable natural kinds. The corresponding position is called “non-reductive ethical naturalism,” or “NEN.” Ethical nonnaturalists, by contrast, argue that moral kinds are genuine and objective, but not natural. (...) This dissertation is largely a challenge to non-reductive ethical naturalism from the viewpoint of ethical nonnaturalism. An introduction, four fairly independent chapters, and a conclusion comprise this dissertation. The introduction (chapter one) situates and summarizes the arguments in the four chapters that immediately follow, and the concluding chapter (chapter six) describes future work related to the arguments in this dissertation. I now turn to chapters two through five. In chapter two, I shore up what I believe are weakness in Derek Parfit’s Triviality Objection to reductive ethical naturalism and then present a challenge to the NEN theorist, which, I argue, the NEN theorist must but ultimately cannot meet. The challenge is to sketch an empirical experiment whereby we can adjudicate between competing moral hypotheses. I explain in terms of experimental design and evaluation why the challenge cannot be met. Chapters three and four focus on the semantics and reference relations of kind terms. In chapter three, I defend the Causal Externalist (CE) theory of semantics and reference against an objection distilled from two articles by Åsa Marie Wikforss. The objection is that CE implies a paradox, escape from which forces the CE theorist upon the horns of a dilemma. I show how the CE theorist can avoid the dilemma by allowing that the intensions of some artificial-kind terms (e.g., ‘jade’) are not given by descriptions associated with the terms. One consequence of this move, however, is that it casts doubt upon the coherence of the claim that moral-kind terms (e.g., ‘morally required action’) are natural-kind terms. In chapter four, I defend Terence Horgan and Mark Timmons’s Moral-Twin Earth argument from three critical responses put forward in recent paper by David Merli. NEN theorists claim that CE can account for the semantics and reference of moral-kind terms. As per Horgan and Timmons (H&T), however, our responses to the Moral-Twin Earth thought experiment give us reason to doubt the NEN theorists’ claim. Against H&T’s argument, however, Merli presents three independent, critical responses, and in this chapter I defend H&T’s argument in a way that is friendly to the ethical nonnaturalist. One upshot is, I contend, that the ethical nonnaturalist can and indeed should co-opt H&T’s argument for his own use. In chapter five, I return to kinds themselves, specifically those in biology. I first point out that ethical nonnaturalism appeals to a metaphysical thesis about nonnatural value, which need not be limited to the moral domain. Then, I argue that biological naturalism alone cannot give a satisfying realist account of biological kinds like HEART and NEURON. Finally, I show that by conjoining the concept of Cummins functions as recently defended by Paul Davies, a thesis about nonnatural value, and Ned Block’s Disney Principle regarding structural properties, the nonnaturalist, unlike the naturalist, can offer a satisfying realist account of biological kinds. (shrink)