Without such assumptions the world of the Naïve Realist would collapse into a disconnected chaos of percepts, without mutual relations, and having no unity within itself. It is clear, however, that Naïve Realism can make these assumptions only by contradicting itself. If it would remain true to its fundamental principle, that only what is perceived is real, then it ought not to assume a reality where it perceives nothing. The imperceptible forces of which perceptible things are the bearers are, in fact, illegitimate hypotheses from the standpoint of Naïve Realism. But because Naïve Realism knows no other realities, it invests its hypothetical forces with perceptual content. It thus transfers a form of existence (the existence of percepts) to a sphere where the only means of making any assertion concerning such existence, viz., sense-perception, is lacking. This self-contradictory theory leads to Metaphysical Realism. The latter constructs, beside the perceptible reality, an imperceptible one which it conceives on the analogy of the former. Metaphysical Realism is, therefore, of necessity Dualistic. Wherever the Metaphysical Realist observes a relation between perceptible things (mutual approach through movement, the entrance of an object into consciousness, etc.), there he posits a reality. However, the relation of which he becomes aware cannot be perceived but only expressed by means of thought. The ideal relation is thereupon arbitrarily assimilated to something perceptible. Thus, according to this theory, the world is composed of the objects of perception which are in ceaseless flux, arising and disappearing, and of imperceptible forces by which the perceptible objects are produced, and which are permanent.