He does not have a theory of truth — Fooloso4
It was along these lines from On Truth and Lies in the Nonmoral Sense:
"The various languages placed side by side show that with words it is never a question of truth, never a question of adequate expression; otherwise, there would not be so many languages. The “thing in itself” (which is precisely what the pure truth, apart from any of its consequences, would be) is likewise something quite incomprehensible to the creator of language and something not in the least worth striving for. This creator only designates the relations of things to men, and for expressing these relations he lays hold of the boldest metaphors… It is this way with all of us concerning language; we believe that we know something about the things themselves when we speak of trees, colors, snow, and flowers; and yet we possess nothing but metaphors for things — metaphors which correspond in no way to the original entities… A word becomes a concept insofar as it simultaneously has to fit countless more or less similar cases — which means, purely and simply, cases which are never equal and thus altogether unequal. Every concept arises from the equation of unequal things. Just as it is certain that one leaf is never totally the same as another, so it is certain that the concept “leaf” is formed by arbitrarily discarding these individual differences and by forgetting the distinguishing aspects. This awakens the idea that, in addition to the leaves, there exists in nature the “leaf”: the original model according to which all the leaves were perhaps woven, sketched, measured, colored, curled, and painted — but by incompetent hands, so that no specimen has turned out to be a correct, trustworthy, and faithful likeness of the original model… We obtain the concept, as we do the form, by overlooking what is individual and actual; whereas nature is acquainted with no forms and no concepts, and likewise with no species, but only with an X which remains inaccessible and undefinable for us."
“What then is truth? A movable host of metaphors, metonymies, and anthropomorphisms: in short, a sum of human relations which have been poetically and rhetorically intensified, transferred, and embellished…”
"To be truthful means to employ the usual metaphors. Thus, to express it morally, this is the duty to lie according to a fixed convention, to lie with the herd and in a manner binding upon everyone… From the sense that one is obliged to designate one thing as “red,” another as “cold,” and a third as “mute,” there arises a moral impulse in regard to truth. The venerability, reliability, and utility of truth is something which a person demonstrates for himself from the contrast with the liar, whom no one trusts and everyone excludes.
"As a “rational” being, he now places his behavior under the control of abstractions. He will no longer tolerate being carried away by sudden impressions, by intuitions. First he universalizes all these impressions into less colorful, cooler concepts, so that he can entrust the guidance of his life and conduct to them. Everything which distinguishes man from the animals depends upon this ability to volatilize perceptual metaphors in a schema, and thus to dissolve an image into a concept.
"If I make up the definition of a mammal, and then, after inspecting a camel, declare “look, a mammal” I have indeed brought a truth to light in this way, but it is a truth of limited value. That is to say, it is a thoroughly anthropomorphic truth which contains not a single point which would be “true in itself” or really and universally valid apart from man.
"At bottom, what the investigator of such truths is seeking is only the metamorphosis of the world into man. He strives to understand the world as something analogous to man, and at best he achieves by his struggles the feeling of assimilation. Similar to the way in which astrologers considered the stars to be in man’s service and connected with his happiness and sorrow, such an investigator considers the entire universe in connection with man: the entire universe as the infinitely fractured echo of one original sound-man; the entire universe as the infinitely multiplied copy of one original picture-man. His method is to treat man as the measure of all things, but in doing so he again proceeds from the error of believing that he has these things [which he intends to measure] immediately before him as mere objects. He forgets that the original perceptual metaphors are metaphors and takes them to be the things themselves.
It is even a difficult thing for [man] to admit to himself that the insect or the bird perceives an entirely different world from the one that man does, and that the question of which of these perceptions of the world is the more correct one is quite meaningless, for this would have to have been decided previously in accordance with the criterion of the correct perception, which means, in accordance with a criterion which is not available. But in any case it seems to me that “the correct perception” — which would mean “the adequate expression of an object in the subject” — is a contradictory impossibility.
"So far as we can penetrate here — from the telescopic heights to the microscopic depths — everything is secure, complete, infinite, regular, and without any gaps. Science will be able to dig successfully in this shaft forever, and the things that are discovered will harmonize with and not contradict each other. How little does this resemble a product of the imagination, for if it were such, there should be some place where the illusion and reality can be divined. Against this, the following must be said: if each us had a different kind of sense perception — if we could only perceive things now as a bird, now as a worm, now as a plant, or if one of us saw a stimulus as red, another as blue, while a third even heard the same stimulus as a sound — then no one would speak of such a regularity of nature, rather, nature would be grasped only as a creation which is subjective in the highest degree."
This is an interesting article about it if you happen to have jstor access:
here.