Sidgwick believed that there are three main differences between Greek ethics and modern ethics. First, he said that in modern ethics the “imperative” or “jural” or “quasi-jural” notions of obligation, duty, and right are central and the focus is on the question, “What is duty and what is its ground?” In ancient ethics, he said, this question is not asked. Instead, it is asked, “Which of the objects that men think good is truly good or the highest good?” And the “attractive” notion of good is central (ME, 106).

Sidgwick's second difference is this: “It was assumed on all sides [by Greek writers on ethics] that a rational individual would make the pursuit of his own good his supreme aim” (ME, 91–2). The modern view, however, can regard it as rational to take as an ultimate aim something different from and even possibly incompatible with one's own good, namely, right or duty or (in one sense) virtue.

Sidgwick thought that this feature of the ancient view, its acceptance of what I shall call “rational egoism,” is compatible with saying that ancient accounts of conduct are “moralities.” On some taxonomies a view does not count as a morality if it either says or is supported by a rationale that says that one's own good is one's ultimate rational end. A taxonomy of this kind holds that such a view is too much like a kind of egoism to be called a morality.