These ideas are of eminent importance for all higher mental development. Mind, in them, departs from that which nature presents, but only in order to take possession of it more securely by systematization and by overcoming the narrow limits of the capacity of consciousness. By separating the common qualities of things from those which vary we classify the things into kinds and species, we think of them as being in various ways related. Instead of having an incomprehensible mass of things standing side by side, we have a system of coördinated and subordinated things, of groups formed according to closer or remoter relationship; and thus it becomes a comparatively easy matter to survey the multitude of things of which nature consists. Not only order, but law too is thus brought into the phenomena of nature. If we collect sticks of wood and set fire to the pile, we notice that some of them burn lustily, others smolder and smoke, still others do not burn at all. Why so? Repetition of similar experiences is necessary before we can give an answer; but mere repetition of the same event does not enable us to give the answer. The event must be broken up and general ideas must be formed out of the elements of the event. Then only can we answer the question. Some of the sticks burn because they are dry. Others do not burn so well or do not burn at all because they are wet. Neither shape nor color nor origin nor many other qualities of the sticks have any causal connection with the difference of burning and not burning. Both order and law in nature are recognized by abstraction.