 The main elements of Moore’s non-naturalism – moral realism and the autonomy of ethics – had been defended earlier by Sidgwick and others and were reasonably well known when Moore wrote. This is reflected in the initial reviews of Principia Ethica, many of which questioned its claims to metaethical originality (see Welchman 1989). But Moore did add two metaethical innovations. One was his view that the fundamental moral concept is “good” (plus its contrary “bad”), which he expressed by saying that goodness is simple and unanalyzable, even in moral terms. This had not been Sidgwick’s view. For him the central moral concept was “ought,” and he defined good in terms of ought, more specifically, as what one ought to desire (1907: 112). Principia Ethica took the exactly opposite view, defining ought in terms of good, so “one ought to do x” literally means “x will produce the most good possible” (1903: 25, 146–48/1993: 76–77, 196–98). But Moore was quickly persuaded by Bertrand Russell that this view is vulnerable to his own open-question argument, since in saying “one ought to do what will produce the most good” we do not mean “what will produce the most good will produce the most good” (Russell 1904: 330). In later work such as Ethics he therefore held that ought is a distinct moral property from good (1912: 173, 180–81/1947: 107–08, 112–13/1965: 73, 76–77; also 1942: 558–59), and in an uncompleted Preface to a planned second edition of Principia Ethica he allowed that it would not affect the essence of his non-naturalism if good were defined in moral terms, say, as what one ought to desire (1993: 5, 14–15). But he continued to prefer the view that good is a simple concept, not definable in deontic terms (1942: 574–77), and there was vigorous debate on this topic in this general period, with Brentano, Broad, and A.C. Ewing defending reductive analyses similar to Sidgwick’s while Ross preferred a non-reductive view like Moore’s. On the Moorean view judgements about the goodness of states of affairs are not shorthand for judgements about how we ought or have reason to respond to those states; they are independent judgements that explain, synthetically but as following “from the very nature” of goodness, why we ought so to respond.