The Philosophical Review/Volume 1/Summary: Mach - Facts and Mental Symbols
Our theories are abstractions, which, while they place in relief that which is important for certain fixed cases, neglect almost necessarily, or disguise, what is important for other cases. We should distinguish sharply between our theoretical conceptions of phenomena and that which we observe. The theoretical conceptions of physics light-waves, molecules, atoms, and energy must be regarded as mere helps or expedients to facilitate our viewing things. Even within the domain of physics the greatest care must be exercised in transferring theories from one department to another, and above all more instruction is not to be expected from a theory than from the facts themselves. Much greater confusion is produced by the direct transference of theories, methods, and inquiries that are legitimate in physics into the field of psychology. The entire theory of the psychological origin of the "external" world by the projection of sensations outwards is founded on a mistaken transference of a physically formulated inquiry into the province of psychology. The artificial and unnecessary dualism of feeling and motion has arisen by the improper formulation of the questions involved. Every physical notion is nothing more than a definite connection of sensory elements. In the sensory sphere of consciousness everything is at once physical and psychical. There is, therefore, no opposition of physical and psychical, no duality, but simply identity.