The profound transmutation undergone by physics in the early years of this century was concomitant with its abrupt awakening from philosophic slumber. Unphilosophic man - the naive realist - believes that the external world closely resembles his perception of it. And the classical physicist, despite certain superficial concessions to subject-object distinctions, remained in all essential respects this naive realist. He really believed that his mechanistic conception, so crudely abstracted from everyday experience, presented a reasonably faithful picture of the physical world. Philosophic man knows better. He knows that while there certainly exists an objective physical reality, those responses to it we call our perceptions are the end-product of an enormously complex, radically constructive, psycho-physiological process; furthermore, that the objectively existing processes which trigger our perceptual responses are often themselves responses triggered initially by our very efforts to perceive the world. So that what the nature of the raw material is at the objective end of this process, he knows we have no means of knowing, unless it be by some equally complex inferential process to which all our empirical knowledge is tributary. And, not through any accession of philosophic wisdom, but because physics had attained that stage of maturity when its discoveries could no longer be accommodated within a naively realistic conceptual framework, the physicist was compelled to recognise as valid this immeasurably more subtle and complex assessment of the true relations existing between observer and observed.
