“Philosophy, in short, may simply be the sort of activity in which we replace ordinary notions and usages by various clear types which bring out interesting issues of principle that the instances covered by these notions and usages can be seen to exhibit in varying degree. Philosophy may in fact be essentially revisionary and creative, though it builds, and must build, on the notions and usages embedded in ordinary thought and speech.” The Discipline of the Cave, p. 53.