tones and colors can be derived with great precision from the laws of mechanical processes, like the vibrations of material particles of air and ether. The second finds that whatever stimulus is applied to a sensory nerve, the nerve always reacts with the same sort of sensation, and conversely, that if the same stimulus affects different nerves, the sensations will belong to different senses. The psychologist, lastly, finds that all the data of sense are instinctively and invariably referred to external existences, and never to the observer's internal condition. Not one of these facts could have been anticipated. The reduction of the brilliancy and variety of tones and colors to the mechanical processes of atoms is surprising. But after agreeing to it, it is no less surprising to discover the specific physiological functions of the sensory nerves, and to find that this does not invalidate the physicist's calculations. Lastly, it remains a mystery how consciousness obtains a knowledge of any existence external to itself. Moreover, the simplest explanations of these several facts are in conflict. We cannot call sense impressions effects of general mechanical processes, if they are at the same time effects of the special constitution of the organs; we cannot call them the latter if they are objective existences alien to consciousness. Hence the difficulty which Dr. Schwarz proposes to solve, and hence also the threefold division of his subject.
He starts from natural ("naïve") realism as the basis of all the scientific theories. In it he distinguishes a metaphysical assertion and a methodological procedure, which are really independent of each other. The procedure asserts three dogmas. (1) It regards touch as the primary sense, and its data as informing us of the real nature of things, and interprets the deliverances of the other senses with reference to touch. This privileged position of the data of touch is due to their relative permanence, while those of the other senses are secondary, because variable. (2) Of these variable data, those which are presented under the customary conditions of observation are regarded as informing us of the properties of things, continuing to exist unperceived, while unwonted and abnormal impressions are treated as transitory appearances. (3) Permanent alterations in the “properties” of things are explained by causation — as effects of the action of other things without the recognition of any interaction. Such is the method whereby natural realism supports its metaphysical assertion of external things independent of our conclusions.
The physicist transforms the world as constituted by natural realism by a method of his own. (1) Remaining under the influence of the realistic dogma as to the supremacy of the tangible, he reduces the “properties” of things to mechanical processes and regards them as the signs of the latter.
