It is widely agreed among philosophers of science today that no formal pattern can possibly be found in the origins of scientific theory. There is no such thing as a "logic of discovery," insists this view--a scientific hypothesis is susceptible to methodological critique only in its relation to empirical consequences derived after the hypothesis itself has emerged through a spontaneous creative inspiration. Yet confronted with the tautly directed thrust of theory-building as actually practiced at the cutting edge of scientific research, (...) this romantic denial of method in the genesis of ideas takes on the appearance of myth. It is the contention of this article that as empirical data ramify in logical complexity, they deposit a hard sediment of theory according to a standard inductive pattern so primitively compelling that it must be recognized as one of the primary forms of inferential thought. This process, here called "ontological induction," is a distillation out of unwieldly observed regularities of more conceptually tractable states hypothesized to underlie them, and is the wellspring of our beliefs in theoretical entities. Previous failure to recognize this pattern of induction has undoubtedly been in substantial measure a result of inadequate attention to the structural details of scientific propositions; for in order to exhibit the nature of ontological induction clearly, it is first necessary to make extended forays through sparsely explored methodological terrain--notably, the nature of scientific "variables," the logical form of "laws," and the type-hierarchy of scientific concepts. (shrink)