The Will to Power · Friedrich Wilhelm Nietzsche
515.
The object is, not "to know," but to schematise,--to impose as much regularity and form upon chaos, as our practical needs require. In the formation of reason, logic, and the categories, it was a need in us that was the determining power: not the need "to know," but to classify, to schematise, for the purpose of intelligibility and calculation. (The adjustment and interpretation of all similar and equal things,--the same process, which every sensual impression undergoes, is the development of reason!) No pre-existing "idea" had anything to do with it: but utility, which teaches us that things can be reckoned with and managed, only when we view them roughly as equal.... _Finality_ in reason is an effect, not a cause: Life degenerates with every other form of reason, although constant attempts are being made to attain to those other forms of reason;--for Life would then become too obscure, too unequal. The categories are "truths" only in the sense that they are the conditions of our existence, just as Euclid's Space is a conditional "truth." (Between ourselves, as no one will maintain that men are absolutely necessary, reason, as well as Euclid's Space, are seen to be but an idiosyncrasy of one particular species of animals, one idiosyncrasy alone among many others....) The subjective constraint which prevents one from contradicting here, is a biological constraint: the instinct which makes us see the utility of concluding as we do conclude, is in our blood, we _are_ almost this instinct.... But what simplicity it is to attempt to derive from this fact that we possess an absolute truth! ... The inability to contradict anything is a proof of impotence but not of "truth."
Text from Project Gutenberg, public domain in the United States.