Why naturalism?

My goal in this paper is to explain what ethical naturalism is, to locate the pivotal issue between naturalists and non-naturalists, and to motivate taking naturalism seriously. I do not aim to establish the truth of naturalism nor to answer the various familiar objections to it. But I do aim to motivate naturalism sufficiently that the attempt to deal with the objections will seem worthwhile. I propose that naturalism is best understood as the view that the moral properties are natural in the sense that they are empirical. I pursue certain issues in the understanding of the empirical. The crux of the matter is whether any synthetic proposition about the instantiation of a moral property is strongly a priori in that it does not admit of empirical evidence against it. I propose an argument from epistemic defeaters that, I believe, undermines the plausibility of a priorism in ethics and supports the plausibility of naturalism.