We simply have no organ for knowing, for “truth”: we “know” (or believe or imagine) exactly as much as is useful to the human herd, to the species: and even what is here called “usefulness” is finally also just a belief, a fiction, and perhaps just that supremely fatal stupidity of which we some day will perish.
(Nietzsche, Gay Science 354)
Written in 1887 as part of the second, expanded edition of The Gay Science, this quote can very nearly serve as an introduction to Nietzsche’s mature thought. Its sentiments lie at the heart of much of his most important work, and are particularly related to his doctrine of perspectivism. That which we think we know we only merely “know”: what we call knowledge is only that which proves useful, in particular that which promotes life. Our human (all too human) perspective first circumscribes what we are able to experience of the world, and from that subset of possibilities we select that which is useful to count as knowledge.
It follows that our usual ideas about human nature, particularly the notions of “self”, “subject”, and “soul” are similarly chosen for their “herd usefulness” rather than their truth. Throughout a number of his works Nietzsche uses this pragmatic notion of truth to demolish the modern, mistaken view of the self as the unitary res cogitans of Descartes, painting a much different picture as a corrective.
We will first briefly examine Nietzsche’s views on truth and knowledge, then discuss his views on language and its relationship to consciousness, and finally examine the corrective version of the self/subject which Nietzsche feels more accurately represents our reality.