When I first came to Vienna from the country, as a boy four or five years of age, and was taken by my father upon the walls of the city's fortifications, I was very much surprised to see people below in the moat and could not understand how, regarded from my point of view, they could have gotten down there; for the thought of another possible way never occurred to me. I remarked the same amazement, once afterwards in life, in the case of a three-year old boy of mine, while taking a walk with him upon the walls about Prague. I recall this feeling to mind every time I engage myself with the reflection above referred to, and I frankly confess that this accidental experience of mine greatly helped to strengthen the opinion upon this point that I adopted a long time ago. The habit of pursuing the same ways in material and psychical things operates to confuse greatly our field of survey. A child forcing its way through a wall in a house in which it has long dwelt, can experience an actual enlargement of its view of the world, and a slight scientific hint can bring much enlightenment.
VIII.
Accordingly, the great chasm between physical and psychological research exists only for the common stereotyped method of observation. A color is a physical object when, for example, we regard its dependence upon its luminous source (upon other colors, upon heat, upon space, and so forth). Regarding however its dependence upon the retina (the elements K L M …), it becomes a psychological object, a sensation. Not the subject-matter, but the direction of our investigation is different in the two domains.
When, from the observation of the bodies of other men or animals, we infer their sensations, as well also as when we investigate the influence of our own body upon our own sensations, we are forced to complete observed facts by analogy. This work of completion by analogy is done with much more accuracy and facility, when it relates, let us say, to nervous processes, which cannot be fully observed in our own bodies—that is when it occurs in the more familiar physical domain—than when the completion relates to psychical processes. Otherwise there is no material difference.
IX.
The thoughts presented gain greatly in fixity and vividness if in addition to simply expressing them in abstract form we bring ourselves face to face with the facts from which they arise. For example, I lie upon my sofa. If I close my right eye the picture represented in the accompanying cut is presented to my left eye. In a frame formed by the ridge of my eyebrow, by my nose, and by my moustache, appears a part of my body, so far as it is visible, and also the things and space about it. My body differs from other human bodies—leaving out of account the fact that every vivid motory idea immediately passes into movement and that contact with it determines more perceptible changes than contact with other bodies—by the circumstance, that it is only partly seen, and, especially, is seen without a head. If I observe an element A within my field of vision, and investigate its connection with another element B within the same field, I go out of the domain of physics into that of physiology or psychology, if B, to use the apposite expression that a friend[20] of mine employed upon seeing this drawing, passes through my skin. Reflections like that for the field of vision may be made with regard to the province of touch and the perceptual domains of the other senses.
[20] J. Popper of Vienna.
[Illustration]
X.
Reference has already been made to the different character of the groups of elements that we have designated by A B C … and α β γ. As a matter of reality, when we see a green tree before us, or remember a green tree, that is conceive a green tree to ourselves, we know right well how to distinguish these two cases. The imaged tree has a much less determinate, a much more changeable form; its green is much paler and more evanescent; and, what is of especial note, it distinctly appears in a different sphere. A movement that we propose to execute is always only a conceived movement, and appears in a different field or sphere from that of the executed movement, which moreover always takes place where the image becomes vivid enough. The statement that the elements A or α appear in a different sphere, means, if we go to the bottom of it, nothing more than that they are united with divers other elements. To this extent, accordingly, the basal component parts in A B C …, α β γ … would be the same (colors, sounds, spaces, times, motory sensations, innervations …), and only the character of their union different.