  At Cambridge Moore was a colleague of Bertrand Russell (1872–1970) and Ludwig Wittgenstein (1889–1951). Russell was not primarily a moral philosopher, but he expressed radically different views at different times about ethics. In 1910 he agreed with Moore that goodness (like roundness) is a quality that belongs to objects independently of our opinions, and that when two people differ about whether a thing is good, only one of them can be right. By 1922 he was holding an error theory (like that of John Mackie, 1917–81) that although we mean by ‘good’ an objective property in this way, there is in fact no such thing, and hence all our value judgments are strictly speaking false (“The Element of Ethics,” Philosophical Essays). Then by 1935 he had dropped also the claim about meaning, holding that value judgments are expressions of desire or wish, and not assertions at all. Wittgenstein's views on ethics are enigmatic and subject to wildly different interpretations. In the Tractatus (which is about logic) he says at the end, ‘It is clear that ethics cannot be put into words. Ethics is transcendental. (Ethics and aesthetics are one and the same.)’ (Tractatus, 6.421). Perhaps he means that the world we occupy is good or bad (and happy or unhappy) as a whole, and not piece-by-piece. Wittgenstein (like Nietzsche) was strongly influenced by Schopenhauer's notion of will, and by his disdain for ethical theories that purport to be able to tell one what to do and what not to do. The Tractatus was taken up by the Logical Positivists, though Wittgenstein himself was never a Logical Positivist. The Logical Positivists held a ‘verificationist’ theory of meaning, that assertions can be meaningful only if they can in principle be verified by sense experience or if they are tautologies (for example, ‘All bachelors are unmarried men.’) This seems to leave ethical statements (and statements about God) meaningless, and indeed that was the deliberately provocative position taken by A.J. Ayer (1910–89). Ayer accepted Moore's arguments about the naturalistic fallacy, and since Moore's talk of ‘non-natural properties’ seemed to Ayer just nonsense, he was led to emphasize and analyze further the non-cognitive ingredient in evaluation which Moore had identified. Suppose I say to a cannibal, ‘You acted wrongly in eating your prisoner.’ Ayer thought I am not stating anything more than if I had simply said, ‘You ate your prisoner.’ I am, rather, evincing my moral disapproval of it. It is as if I had said, ‘You ate your prisoner’ in a peculiar tone of horror, or written it with the addition of some special exclamation marks (Language, Truth and Logic, 107–8).