Nietzsche (from “On Truth and Lying in an Extra-Moral Sense”):
What, then, is truth? A mobile army of metaphors, metonyms, and anthropomorphisms — in short, a sum of human relations which have been enhanced, transposed, and embellished poetically and rhetorically, and which after long use seem firm, canonical, and obligatory to a people: truths are illusions about which one has forgotten that this is what they are; metaphors which are worn out and without sensuous power; coins which have lost their pictures and now matter only as metal, no longer as coins.
We still do not know where the urge for truth comes from; for as yet we have heard only of the obligation imposed by society that it should exist: to be truthful means using the customary metaphors — in moral terms: the obligation to lie according to a fixed convention, to lie herd-like in a style obligatory for all. Now man of course forgets that this is the way things stand for him. Thus he lies in the manner indicated, unconsciously and in accordance with habits which are centuries' old; and precisely by means of this unconsciousness and forgetfulness he arrives at his sense of truth.
Owen Barfield (from Poetic Diction):
We must, therefore, imagine a time when spiritus or pneuma, or older words from which these had descended, meant neither breath, nor wind, nor spirit, nor yet all three of these things, but when they simply had their own old peculiar meaning, which has since, in the course of the evolution of consciousness, crystallized into the three meanings specified – and no doubt into others also, for which separate words had already been found by Greek and Roman times.