In knowledge we are concerned with questions which arise for us through the fact that a world of percepts, conditioned by time, space, and our subjective organisation, stands over against a world of concepts expressing the totality of the universe. Our task consists in the assimilation to one another of these two spheres, with both of which we are familiar. There is no room here for talking about limits of knowledge. It may be that, at a particular moment, this or that remains unexplained because, through chance obstacles, we are prevented from perceiving the things involved. What is not found to-day, however, may easily be found to-morrow. The limits due to these causes are only contingent, and must be overcome by the progress of perception and thought. Dualism makes the mistake of transferring the opposition of subject and object, which has meaning only within the perceptual world, to pure conceptual entities outside this world. Now the distinct and separate things in the perceptual world remain separated only so long as the perceiver refrains from thinking. For thought cancels all separation and reveals it as due to purely subjective conditions. The Dualist, therefore, transfers to entities transcending the perceptual world abstract determinations which, even in the perceptual world, have no absolute, but only relative, validity. He thus divides the two factors concerned in the process of knowledge, viz., percept and concept, into four: (1) the object in itself; (2) the percept which the subject has of the object; (3) the subject; (4) the concept which relates the percept to the object in itself. The relation between subject and object is "real"; the subject is really (dynamically) influenced by the object. This real process does not appear in consciousness. But it evokes in the subject a response to the stimulation from the object. The result of this response is the percept. This, at length, appears in consciousness. The object has an objective (independent of the subject) reality, the percept a subjective reality. This subjective reality is referred by the subject to the object. This reference is an ideal one. Dualism thus divides the process of knowledge into two parts. The one part, viz., the production of the perceptual object by the thing-in-itself, he conceives of as taking place outside consciousness, whereas the other, the combination of percept with concept and the latter's reference to the thing-in-itself, takes place, according to him, in consciousness.