  Moore assumes that this will be true of every putative naturalistic definition of goodness, whether it be in terms of second-order desires, social approval, being more evolved, or whatever. All of these naturalistic definitions would fail the open question argument. If he is right, and goodness cannot be defined wholly with reference to concepts from the empirical sciences, then goodness is a sui generis notion, i.e., is one that can only be understood in its own, evaluative terms.