In this belief there _reigns_ the sensual and coarse prejudice that our sensations teach us _truths_ concerning things,--that I cannot at the same moment of time say of one and the same thing that it is _hard_ and _soft._ (The instinctive proof, "I cannot have two opposite sensations at once," is quite _coarse_ and _false_.) That all contradiction in concepts should be forbidden, is the result of a belief, that we _are able_ to form concepts, that a concept not only characterises but also _holds_ the essence of a thing.... As a matter of fact, logic (like geometry and arithmetic) only holds good of _assumed existences which we have created._ Logic is _the attempt on our part to understand the actual world according to a scheme of Being devised by ourselves; or, more exactly, it is our attempt at making the actual world more calculable and more susceptible to formulation, for our own purposes...._ 517. In order to be able to think and to draw conclusions, it is necessary to _acknowledge that which exists:_ logic only deals with formulæ for things which are constant. That is why this acknowledgment would not in the least prove reality: "that which is" is part of our optics. The ego regarded as Being (not affected by either Becoming or evolution). The _assumed world_ of subject, substance, reason, etc., is necessary, an adjusting, simplifying falsifying, artificially-separating power resides in us. "Truth" is the will to be master over the manifold sensations that reach consciousness; it is the will to _classify_ phenomena according to definite categories. In this way we start out with a belief in the "true nature" of things (we regard phenomena as real). The character of the world in the process of Becoming _is not susceptible of formulation;_ it is "false" and "contradicts itself." _Knowledge_ and the process of _evolution_ exclude each other. _Consequently,_ knowledge must be something else: it must be preceded by a will to make things knowable, a kind of Becoming in itself must create the _illusion_ of _Being._ 518. If our "ego" is the only form of Being, according to which we make and understand all Being: very good! In that case it were very proper to doubt whether an _illusion_ of perspective were not active here--the apparent unity which everything assumes in our eyes on the horizon-line. Appealing to the body for our guidance, we are confronted by such appalling manifoldness, that for the sake of method it is allowable to use that phenomenon which is _richer_ and more easily studied as a clue to the understanding of the poorer phenomenon. Finally: admitting that all is Becoming, _knowledge is only possible when based on a belief in Being._ 519.