  Following his own prescription for an affirmative and constructive philosophy, Williams worked steadily towards the development of his own distinctive position in metaphysics. He introduced the useful division of the subject into Speculative Cosmology, which deals with the basic elements making up the world we live in, such as matter, mind, and force, together with the relations between them, and Analytic Ontology, which explores the fundamental categories, such as Substance and Property, and how they relate to one another. Speculative Cosmology, in particular, needs to be open to developments in the fundamental sciences, and so needs to be seen as always provisional and a posteriori. Analytic Ontology, the exploration of the categories of being, is a more purely reflective and a priori discipline aiming to elucidate the range of different elements in any universe.