 Maritain’s account supposes that there is a metaphysical and epistemological hierarchy: of sensible, observable things as known through the senses, to “the intelligible necessities immersed in the reality of this world of existence” which are known through the intellect disengaged from the senses (Degrees of Knowledge, 1932 [1959: 145]), to the “universe of quantity as such” (mathematics), to metaphysics and, ultimately, to mystical experience (see 1932 [1959: 145–6]). The levels in this hierarchy are determined, then, by how and the extent to which what is known is abstracted from matter. The philosophy of nature, then, is a deductive science that lies at the first level of abstraction. It is close to metaphysics in that it addresses general issues concerning the universe, such as its relation to principles of necessity and contingency, and to a first cause. But it also needs to be completed by a knowledge of the natural sciences, and so is at the same level of abstraction.