Alasdair MacIntyre, answered from the texts and cited to the page.
Kant, Mill, Hume — the canonical Enlightenment moralists — set themselves a task they could not complete: to justify morality on grounds that did not presuppose the older Aristotelian framework of human function and telos that they had rejected.1 Each failed in characteristic ways. Kant's appeal to the categorical imperative, on examination, generates valid maxims only when supplemented by substantive content the imperative cannot itself supply.
Mill's appeal to utility presupposes a substantive account of what utility consists in, an account utilitarianism cannot give without circularity. Hume's appeal to sentiment fails to bridge the gap his own argument opened between fact and value. Nietzsche correctly diagnosed the failure: when moral discourse cannot ground itself rationally, what remains is the will to power masked as duty or right or utility.
On the Genealogy of Morals is the unanswerable critique of the Enlightenment project from within. The question Nietzsche could not answer is whether the failure was inevitable. It was not. The Enlightenment project failed because it abandoned the Aristotelian framework of telos, function, and virtue, and tried to derive morality from premises that lacked the resources to ground it.
The recovery of that older framework — Aristotelian and ultimately Thomist — is the rational alternative to Nietzsche's nihilism.2345
At the same time as they agree largely on the character of morality, they agree also upon what a rational justification of morality would have to be. Its key premises would characterize some feature or features of human nature; and the rules of morality would then be explained and justified as being those rules which a being possessing just such a human nature could be expected to accept.After Virtue - A Study in Moral Theory, p. 68
Yet it is not of course just that Nietzsche's moral philosophy is false if Aristotle's is true and vice versa. In a much stronger sense Nietzsche's moral philosophy is matched specifically against Aristotle's by virtue of the historical role which each plays.After Virtue - A Study in Moral Theory, pp. 133–134
Nietzsche did of course assert that the most skilful dialectical reasoning had in fact failed by its own standards as well as by his, especially in ethics, in theology, and in antitheology. He had nothing but scorn for both Kant and Mill.Three Rival Versions of Moral Enquiry, pp. 47–48
"Man," wrote Nietzsche, "does not pursue happiness; only the Englishman does that" ('Maxims and Arrows,' No. 12, Götzendämmerung). But this type of pretension is, after all, on the genealogist's view, characteristic of the whole history of morality.Three Rival Versions of Moral Enquiry, pp. 181–182
The outcome of these debates is, however, now clear. In moral philosophy the central question which the participants in those debates had hoped to answer was: What are those principles gov erning action to which no rational human being can deny his or her assent?Whose Justice Which Rationality, p. 176
The structural argument of After Virtue's critical half. Defended through the rest of the corpus. The standard Kantian counter-objection (Korsgaard, O'Neill, Rawls) is that Kant succeeds where MacIntyre says he fails, that the categorical imperative does generate substantive content. The standard utilitarian counter-objection is that utility's content can be filled by preference-satisfaction or welfare without circularity. Bernard Williams's third way — a sophisticated naturalism without Aristotelian metaphysics — is, on careful examination, closer to Nietzsche than to Aristotle.