 Still, while Lewis’s method of philosophical inquiry is certainly not “bottom-up”, in my opinion it is best to present the results of that inquiry in a bottom-up fashion. That is what this essay, and ones to follow, will attempt to do. I will divide the terrain into four parts: Lewis’s fundamental ontology; his theory of metaphysical modality; his “applied” metaphysics (covering such topics as laws of nature, counterfactuals, causation, identity through time, and the mind); and Lewisian methodology in metaphysics. I’ll explain these distinctions shortly, but be advised that the present essay will almost exclusively address the first of these four topics. Other aspects of Lewis’s thought are covered in the general entry on  David Lewis.