The ethical tradition of natural law is often viewed rather narrowly as that part of Roman Catholic moral teaching not reliant on revelation. But this sort of proprietary identification casts too sectarian a light on its value. I shall treat the tradition as a much broader church. It will thus encompass some theorists whose inclusion might surprise, but I do not propose a treatment that is so generous as to remove any sense that there is something distinctive covered by the heading “natural law.” The recognition that natural law is, like all traditions, a family of theories, insights, and ideas need not drive us into thinking of it as too extended a family. We should not, for instance, see it as equivalent to all theories that reject relativism, conventionalism, and positivism in law or ethics. These really have too little in common to form even a loose tradition.

Perhaps the best way forward is to specify some traits that have been common to a number of theories historically associated with the idea that understanding morality is a matter of grasping something about the underlying rationality of the universe with respect to the place of human beings (or rational agents) in it. This “something” is discovered in reality rather than constructed by human will, but it reveals that the good for agents is a matter of acting well in accord with nature.