I explore the idea that realism and instrumentalism are complementary rather than incompatible aspects of modern physical science.  Both abstract theoretical quantities and the empirically applicable methods we have for measuring these quantities are equally necessary in the characteristic methodology of modern physics already epitomized in the work of Isaac Newton—which, among many other things, first resolved the classical problem of realism vs. instrumentalism concerning the true motions in the Solar System.  This approach also sheds light on the duality of understanding and sensibility, concepts and intuitions, in the transcendental idealism of Immanuel Kant, which was itself very much inspired by Newton’s work.  Time permitting, I shall also explore how this Newtonian-Kantian approach continues in post-Newtonian physics, beginning with James Clerk Maxwell’s theory of the electro-magnetic field.