=The World of Knowledge.= There is this to be observed about the threefold realm of Kant: the realm of subjectivity and that of knowledge together make up our conscious life. One is the realm of the conscious individual, and the other the realm of the consciousness of humanity. Kant conceived this further distinction between the two realms: in a purely subjective state the mind is entirely passive and its content is without control; in a state of knowing the mind is actively engaged in collecting and relating its ideas. This is called by Kant synthesis. When Kant was formulating his problem, there gradually came to him in clearer outline the synthetic nature of the activity of the human reason. He felt more and more that the secret of the knowing process was to be explained by its function of combining many experiences into a unity. This conception of synthesis is what separates the _Critique of Pure Reason_ from all the previous writings of Kant. Furthermore, the three books of the _Critique_ are expositions of the different stages in which mental synthesis completes itself: in (1) perception, (2) understanding, and (3) reason. The knowing activity of man develops in these three different forms of synthesis, in which each lower stage is the content of the higher. What, then, is the central factor in knowledge? It is the synthetic power of the mind. The mind is not merely passively aware of its sensations as they come _seriatim_, but it actively relates them and holds them together. The mind is a dynamic agent whose activity consists in synthesizing in the present moment its experiences of the past. The human mind is not like a curtain upon which stereopticon pictures appear and then disappear in turn. It retains its pictures, although they are no longer being thrown upon the screen. Suppose we hear the ticking of a clock. Now if we had no synthetic power, all we should apprehend would be one, one, one,――and so on. But we do have synthetic power, and we say one, two, three, and so on. We count in a series in which each term includes the preceding term. Two includes one, and three includes two, etc. This is knowledge. It is cumulative experience. The experience of twenty animals, each having one experience, is not the same as the experience of one man having twenty experiences. In vain would nature act on man if the mind of man through memory and imagination did not carry over experiences. So the important thing is not what happens, but what power the human mind has. Knowledge, then, to Kant is the unifying of the manifold.