The science of the intellect has ever wrestled with one peculiar fact. It found knowledge which the mind had received from the outside, so-called empirical knowledge. But it also found knowledge which was innate, so-called _a priori_ knowledge. That there is always a valley between two mountains, that gold is not sheet iron, that the part is smaller than the whole, that the angles of a triangle are together equal to two right angles, that circles are round, that water is wet, that fire is hot, etc., these are things of which we know that they are true in heaven and in hell, and in all time to come, although we have never been there with our experience. This plainly shows that we harbor a secret in our brains which the lovers of the mystical seek to exploit by making believe that their self-interested wisdom of God and high authority likewise belongs to the eternally innate truths. For this reason it is especially important for the proletariat to bring the controversy of the origin and source of understanding to a close. Our logic asks: Does wisdom descend mysteriously from the interior of the human brain, or does it come from the outer world like all experience? We shall leave its descent from heaven out of the question. The answer is: Science, perception, understanding, thought, require internal and external things, subject and object, brain and world. Truth is here and truth is there. Truth is so divine that it is everywhere and absolute. But how to explain that wonderful _a priori_ knowledge which exceeds all experience? For it is a fact that the intellect has not alone the faculty of knowing things in general, but also that of separating them into their parts and from one another and to name them. It cuts off slices, so to say. But not like the butcher who sees everything merely from the standpoint of his trade. You will remember from your own experience as well as from my repeated statements that the world is not a monotonous, but a multiform unit. This confused knot is dissolved and explained by intellectual separation, by classification. In the absolute everything is alike and unlike. But the intellect makes abstractions from the unlike. For instance, in conceiving of the term minerals, we pass over the distinction between gold and sheet iron. Then, when we continue the classification by subordinating gold and sheet iron as separate species to the general term of minerals, we know very well that gold and sheet iron are different kinds of the same general mineral nature. We know what the names indicate, and so long as they retain their meaning, we know that neither in heaven nor in hell can gold be sheet iron or sheet iron be gold. Water and fire are specialties taken from the universe and named. Is it a wonder, then, that these names have a special meaning and that we have the settled conviction that wherever sense instead of nonsense is master, fire burns, water wets, circles are