Some philosophers have denied not only the existence of objects, but also the reality of space. What is space but a certain group of experiences? The conception of space originates by moving and by being moved about. The conception of space is the consciousness that by moving, or by being moved, a change is effected; that is, a certain object serving as a point of reference is either approached or left at a greater distance. The acts of approach or withdrawal are as much realities as are any other acts of the subject. Discussions concerning the reality of space accordingly become mere verbal quibbles as soon as we understand by space the condition common to all motion-experiences.
The mental state in which through contact with external facts one or several of the senses are affected so as to produce a direct awareness of their presence, is called perception. The effects of external facts upon the sense of touch appear as different forms of resistance. To the other senses they appear as odors, tastes, sounds, and images. All these sensations are so many subjective methods of representing certain objective processes. Perceptions represent immediate reality because the objects perceived, i. e., the objects represented by an image in the eye, a taste on the tongue, etc., are in an immediate contact with our senses. The feeling subject is directly conscious of their existence by their present effects. They are our _Anschauung_, i. e., the living presence of objective reality.
Besides this living presence of objective reality, of which our immediate surroundings consist,—besides our _Anschauung_—, man is in possession of more general representations, which comprise all the memories of a certain class of percepts. We call them concepts. Man alone through the mechanism of word-symbols has been able to form concepts. Abstract reasoning as well as scientific thought will grow with the assistance of concepts in the course of a higher development.
The higher we rise in the evolution of representative feelings, i. e., in the development of mind, the more numerous are the opportunities for going astray. A scientific hypothesis, if erroneous, is more sweeping in its fallacies than a single hallucination, which is a misinterpretation merely of certain feelings. The subjective part of an hallucination, namely the feeling itself, is real; but the objective part, the representative element of the feeling, is not real; that which it is supposed to mean, does not exist. The interpretation of the feeling is erroneous in a hallucination.