For many evaluative terms it is useful to distinguish, following John Rawls, between concepts and conceptions of them; for instance, on the one hand there are questions about what it means to be good, on the other there are questions about which specific things actually are good. This distinction helps explain why many evaluative terms allow much more disagreement than other terms; two people can agree about what it means to be good (concept) and still disagree entirely about which concrete things are good (conceptions), whereas people could hardly agree on what it means to be, say, a knife and still widely disagree about which objects are knives.

Although it is not a distinction drawn by all moral philosophers, this split between concept and conception does set its mark on the literature in the sense that there are two main lines of inquiry about the good...