  By far the most famous and influential argument against moral naturalism is G.E. Moore’s Open Question Argument (Moore 1903, 5–21). Moore’s thought is as follows. Suppose “\(N\)” to abbreviate a term expressing the concept of some natural property \(N\), maximally conducing to human welfare perhaps, and suppose a naturalist proposes to define goodness as \(N\)-ness. We swiftly show this to be false by supposing someone to ask of something acknowledged to be \(N\), whether it was good. This, Moore urges, is an open question. The point is, essentially, that it is not a stupid question in the sort of way, “I acknowledge that Jimmy is an unmarried man but is he, I wonder, a bachelor?” is a stupid question: if you need to ask it, you don’t understand it. Given what the words concerned mean, the question of whether a given unmarried man is a bachelor is, in Moore’s terminology, closed—there is no way for a conceptually competent individual to be in doubt about the answer to this question. So goodness and \(N\)-ness, unlike bachelorhood and unmarried-man-hood, are not one and the same.