First, we shall consider the distinction as set forth in Principia. Next, on the basis of what Moore says there, a view as to the nature of universals will be attributed to him. This view will provide the ground for a radical distinction between natural and non-natural properties. But it will not quite jibe with other things he says at a slightly later period. Nor will it be clear why he holds to such a view of universals. Finally we shall (...) consider a very early paper of Moore's, written just prior to Principia. An analysis of this paper will reveal a rather strange and complex ontology implicit in it. This, in turn, will show the source of the ontology of Principia; why the ontology attributed to him in Principia does not jibe with other things he says; and the origin of the notion of non-natural properties. (shrink)