#Fechner's simile.#
For the same reason Professor Mach objects to Fechner's comparison. Yet it seems to me that Fechner hit the mark when he compared feeling and motion to the inside and the outside curves of a circle; they are entirely different and yet the same. The inside curve is concave, the outside curve is convex. If we construct rules relating first to the concave inside and then to the convex outside, we shall notice a parallelism in the formulas; yet this parallelism will appear only in the abstractions which have been made of one and the same thing from different standpoints and serving different purposes. The abstract conceptions form two parallel systems, but the real thing can be represented as parallel only in the sense that it is parallel to itself. If we consider the real thing, it represents a parallelism of identity. There is but one line, and this one line is concave if viewed from the inside, it is convex if viewed from the outside.
#The simile of a sheet of paper.#
The simile which I introduced of the two sides of one and the same sheet of paper was devised to convey no other meaning than this construction of Fechner's comparison. The paper is invested with a metaphysical rôle only in the case where the simile is otherwise construed. There is no page which exists of itself as a mere mathematical plane independent of the paper of which it forms a side. Thus there can never be in reality a page without its counterpage. The paper, its size and color, belong to the page and constitute its properties.
Thus the abstraction 'feeling' represents my looking at the one side of reality. I leave, and from the subjective standpoint I have to leave, the other side out of account. Yet the other side of the sheet is inseparable from the one at which I am now looking, just as much as feeling is inseparable from motion. And I am constrained to admit the truth of the reverse also: motion is inseparable from feeling, but with the limitation that motions need not be on their subjective side actual feelings; they may be only elements of feeling which under certain conditions become actual.
#The metaphysical misinterpretation.#
I am aware that my comparison of feeling and motion to the two sides of one sheet of paper may be easily misinterpreted. But is not that a danger to which all comparisons are subject? A comparison is always imperfect, or as the Romans used to say, it limps: "Omne simile claudicat." And is not reality liable to be misinterpreted in the same way? Have not some philosophers thus introduced the metaphysical explanation of the unknowableness of things in themselves? Such philosophers conceive the two sides of a sheet of paper (the abstract mathematical planes of the pages) as phenomenal and the paper as their metaphysical essence. The size of the sheet, the color of the paper, and all its other qualities are in a metaphysical world-conception represented as properties of which the thing is possessed—not as constituting the thing, but as essentially different from it.
It appears to me that Professor Mach in spite of his opposition to Fechner's simile and to the expression that feeling and motion are two aspects of one and the same reality, entertains the same view. At least his words: "Only the relation in which we consider them makes them at one time physical elements, at another time feelings," are to that effect.
II. SENSATIONS AND THOUGHTS.
#Professor Mach's problem.#