In rational inquiry, we idealize to selected domains in such a way (we hope) as to permit us to discover crucial features of the world. Data and observations, in the sciences, have an instrumental character. They are of no particular interest in themselves, but only insofar as they constitute evidence that permits one to determine fundamental features of the real world, within a course of inquiry that is invariably undertaken under sharp idealizations, often implicit and simply common understanding, but always present.