The scope of the philosophy of science is sufficiently broad to encompass, at one extreme, conceptual problems so intimately connected with science itself that their solution may as readily be regarded a contribution to science as to philosophy and, at the other extreme, problems of so general a philosophical bearing that their solution would as much be a contribution to metaphysics or epistemology as to philosophy of science proper. Similarly, the range of issues investigated by philosophers of science may be so narrow as to concern the explication of a single concept, considered of importance in a single branch of science, and so general as to be concerned with structural features invariant to all the branches of science, taken as a class. Accordingly, it is difficult to draw boundaries that neatly separate philosophy of science from philosophy, from science, or...