 As we’ve already seen, part of Lewis’s significance came from the breadth of subject matter on which he made major contributions. It is hard to think of a philosopher since Hume who has contributed so much to so many fields. And in all of these cases, Lewis’s contributions involved defending, or in many cases articulating, a big picture theory of the subject matter, as well as an account of how the details worked. Because of all his work on the details of various subjects, his writings were a font of ideas even for those who didn’t agree with the bigger picture. And he was almost invariably clear about which details were relevant only to his particular big picture, and which were relevant to anyone who worked on the subject.