It is well to speak here of truth as Nietzsche conceived it. We have seen how he denied its absolutism and declared it to be relative. But in his present work he goes further and contends that the feeling of the increase of power is the determining factor in truth. If, as we have seen, the "truths" of science are merely those interpretations which grow out of the scientists' will to power, then truth itself must be the outgrowth of this instinct. That which makes for the growth and development of the individual--or in other words, that which increases the feeling of strength--is necessarily the truth. From this it is easy to deduce the conclusion that in many instances truth is a reversal of facts, for preservation very often consists in an adherence to actual falsity. Thus, the false causality of certain phenomena--the outcome of logic engendered by a will to power--has not infrequently masqueraded as truth. Nietzsche holds that this doctrine contains the only possible definition of truth; and in this doctrine we find an explanation for many of the apparent paradoxes in his teachings when the matter of truth and falsity are under discussion.
The second part of the first book relates to the will to power in nature, and contains the most complete and lucid explanation of Nietzsche's basic theory to be found anywhere in his writings. This section opens with an argument against a purely mechanical interpretation of the world, and a refutation of the physicists' concept of "energy." The chemical and physical laws, the atomic theory and the mechanical concept of movement, he characterises as "inventions" on the part of scientists and researchers for the purpose of understanding natural phenomena and therefore of increasing their feeling of power. The apparent sequence of phenomena which constitutes "law" is, according to Nietzsche, only a "relation of power between two or more forces"--a matter of interdependence, a process wherein the "procession of moments do _not_ determine each other after the manner of cause and effect." In these observations we see the process of reasoning with which Nietzsche refutes the current methods of ascertaining facts and the manner in which he introduces the principle of will to power into the phenomena of nature.