Philippa Foot, answered from the texts and cited to the page.
Moral judgement cannot be subjective in the way that aesthetic preferences are subjective. The decisive thought is the Holocaust: if morality is the expression of attitude, there is no substance to saying "we are right and the Nazis are wrong" — only a stand-off of attitudes, with no possibility of error. This is intolerable. The noncognitivist tradition (Stevenson, Ayer, Hare) construed the conditions of use of sentences like "It is morally wrong to kill innocent people" in terms of the speaker's feelings, attitudes, or commitments to act, and thereby produced a gap between the facts of a case and the moral judgement about it.1234
The route out runs through the virtues. Virtue concepts (courage, temperance, wisdom, justice) have necessary connections to facts about human good and harm; the descriptive-evaluative distinction collapses for them. Loquacity is a vice because there is a reason it is a vice, having to do with the human good. From this start, an objective foundation for moral judgement becomes possible — completed in Natural Goodness with the species-form argument.5
This is the subjectivism—often called 'non-cognitivism'—that came to the fore with A. J. Ayer, C. L. Stevenson, and Richard Hare, informed the work of John Mackie and many others, and has lately appeared, refreshed, in Allan Gibbard's 'expressivist' account of normative language.Natural Goodness, pp. 5–6
For moral evaluation, something 'conative'had to be present as well as belief in matters of fact. p. 192 What all these theories try to do, then, is to give the conditions of use of sentences such as 'It is morally objectionable to break promises', in terms of something that must be true about the speaker.Moral Dilemmas and Other Topics, pp. 114–115
It was recognized, of course, that the language contains many terms like 'courage' or 'justice' designed for description as well moral judgement, but it was said that their 'descriptive' content could not reach all the way to moral evaluation, the speaker's feelings or commitments to action having to be added if that were to be on the scene.Moral Dilemmas and Other Topics, p. 114
Their theories were devised to take account of something that really is a feature of moral judgement: the 'action-guiding' character of morality, which Hume had insisted on and taken as the foundation of his moral philosophy. Morality, Hume had said, is necessarily practical, serving to produce and prevent action, and I shall call this 'Hume's practicality requirement'.Natural Goodness, p. 7
It was reading Aquinas on the individual virtues that first made me suspicious of contemporary theories about the relation between 'fact' and 'value'; and I have thought about virtues and vices xii INTRODUCTION on and off for the last twenty years. Meanwhile I was moving, a step at a time, away from the theories of philosophers such as C. L. Stevenson and R. M. Hare.Virtues and Vices, pp. 16–17
Anti-noncognitivism inaugurates contemporary virtue ethics. Anscombe's "Modern Moral Philosophy" (1958) is the parallel founding text. Foot, Anscombe, and MacIntyre between them mounted the most sustained mid-late-twentieth-century anti-subjectivist project; Hursthouse and McDowell developed it. The contemporary opponent is Allan Gibbard's expressivism (Wise Choices, Apt Feelings 1990, Thinking How to Live 2003) and Simon Blackburn's quasi-realism — both more sophisticated successors to the original noncognitivism. Mackie's error theory remains a live position. The metaethics field is not settled.