…the process of living always grows out of or is based on certain assumptions: these are like the soil on which we stand, or which we use as a point of departure.

And this is true in every field.…Every idea is thought, every picture is painted, out of certain assumptions or conventions which are so basic, so firmly fixed for the one who thought the idea or painted the picture that he neither pays heed to them, nor, for that matter, introduces them into his picture or idea; nor do we find them there in any guise except as presupposed and left, as it were, to one side. This is why we sometimes fail to understand an idea or a picture; we lack the clue to the enigma, the key to the secret convention.