For how could any one communicate by word of mounth that he has seen? And how could that which has been seen be identical to a listener if he has not seen it? He who speaks, speaks, but does not speak a color or a thing. When, therefore, one has not a thing in the mind, how will he get it there from another person by word or any other token of the thing except by seeing it, if it is a color, or hearing it, if it is a noise? For he who speaks does not speak a noise at all, or a color, but a word.
But even if it is possible to know things, and to express whatever one knows in words, yet how can the hearer have in his mind the same thing as the speaker? For the same thing cannot be present simultaneously in several separate people; for in that case the one would be two.
But if the same thing could be present in several persons, there is no reason why it should not appear dissimilar to them, if they are not themselves entirely similar and are not in the same place; for if they were in the same place they would be one and not two. So a man can scarcely perceive the same thing as someone else.