On the Recollection of Things Mathematical.

19. The memory containeth also the reasons and innumerable laws of numbers and dimensions, none of which hath any sense of the body impressed, seeing they have neither colour, nor sound, nor taste, nor smell, nor sense of touch. I have heard the sound of the words by which these things are signified when they are discussed; but the sounds are one thing, the things another. For the sounds are one thing in Greek, another in Latin; but the things themselves are neither Greek, nor Latin, nor any other language. I have seen the lines of the craftsmen, even the finest, like a spider’s web; but these are of another kind, they are not the images of those which the eye of my flesh showed me; he knoweth them who, without any idea whatsoever of a body, perceives them within himself. I have also observed the numbers of the things with which we number all the senses of the body; but those by which we number are of another kind, nor are they the images of these, and therefore they certainly are. Let him who sees not these things mock me for saying them; and I will pity him, whilst he mocks me.

Conf 12.13.1