QUOTE : Every mathematical idea presents itself to us with the character of a construction after the fact, a reconquest. Cultural constructions never have the solidity of natural objects. They are never there in the same way. Each morning, after night has intervened, we must make contact with them again. They remain impalpable; they float in the air of the village but the countryside does contain them. If, nevertheless, in the fullness of thought, the truths of culture seem to us the measure of being, and if so many philosophies posit the world upon them, it is because knowledge continues upon the thrust of perception. It is because knowledge uses the world-thesis which is its fundamental sound. We believe truth is eternal because truth expresses the perceived world and perception implies a world which was functioning before it and according to principles which it discovers and does not posit. In one and the same movement knowledge roots itself in perception and distinguishes itself from perception. Knowledge is an effort to recapture, to internalize, truly to possess a meaning that escapes perception at the very moment that it takes shape there, because it is interested only in the echo that <br />being draws from itself, not in this resonator, its own other which makes the echo possible. Perception opens us to a world already constituted and can only reconstitute it.