It is from a Dualism such as this that there arises the distinction between the object of perception and the thing-in-itself, which Kant introduced into philosophy, and which, to the present day, we have not succeeded in expelling. According to our interpretation, it is due to the nature of our organisation that a particular object can be given to us only as a percept. Thought transcends this particularity by assigning to each percept its proper place in the world as a whole. As long as we determine the separate parts of the cosmos as percepts, we are simply following, in this sorting out, a law of our subjective constitution. If, however, we regard all percepts, taken together, merely as one part, and contrast with this a second part, viz., the things-in-themselves, then our philosophy is building castles-in-the-air. We are then engaged in mere playing with concepts. We construct an artificial opposition, but we can find no content for the second of these opposites, seeing that no content for a particular thing can be found except in perception. Every kind of reality which is assumed to exist outside the sphere of perception and conception must be relegated to the limbo of unverified hypotheses. To this category belongs the "thing-in-itself." It is, of course, quite natural that a Dualistic thinker should be unable to find the connection between the world-principle which he hypothetically assumes and the facts that are given in experience. For the hypothetical world-principle itself a content can be found only by borrowing it from experience and shutting one's eyes to the fact of the borrowing. Otherwise it remains an empty and meaningless concept, a mere form without content. In this case the Dualistic thinker generally asserts that the content of this concept is inaccessible to our knowledge. We can know only that such a content exists, but not what it is. In either case it is impossible to transcend Dualism. Even though one were to import a few abstract elements from the world of experience into the content of the thing-in-itself, it would still remain impossible to reduce the rich concrete life of experience to those few elements, which are, after all, themselves taken from experience. Du Bois-Reymond lays it down that the imperceptible atoms of matter produce sensation and feeling by means of their position and motion, and then infers from this premise that we can never find a satisfactory explanation of how matter and motion produce sensation and feeling, for "it is absolutely and for ever unintelligible that it should be other than indifferent to a number of atoms of carbon, hydrogen, and nitrogen, etc., how they lie and move, how they lay or moved, or how they will lie and will move. It is in no way intelligible how consciousness can come into existence through their interaction." This conclusion is characteristic of the whole tendency of this school of thought. Position and motion are abstracted from the rich world of percepts.