No, indeed, I replied; and the same is true of most, if not all, the other senses—you would not say that any of them requires such an addition?
Certainly not.
But you see that without the addition of some other nature there is no seeing or being seen?
How do you mean?
and, unlike the other senses, requires the addition of a third nature before it can be used. This third nature is light. Sight being, as I conceive, in the eyes, and he who has eyes wanting to see; colour being also present in them, still [E]unless there be a third nature specially adapted to the purpose, the owner of the eyes will see nothing and the colours will be invisible.
Of what nature are you speaking?
Of that which you term light, I replied.
True, he said.
[508] Noble, then, is the bond which links together sight and visibility, and great beyond other bonds by no small difference of nature; for light is their bond, and light is no ignoble thing?
Nay, he said, the reverse of ignoble.