Of what nature are you speaking?
Of that which you term light, I replied.
Noble 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.
Any one who has common sense will remember that the bewilderments of the eyes are of two kinds, and arise from two causes, either from coming out of the light or from going into the light, which is true of the mind’s eye as much as of the bodily eye.
Plato’s The Republic, Book VI