In order to judge intelligently, then, about light and colors as well as all other sensible qualities, the sensation of color must be carefully distinguished from the movement of the optic nerve, and reason must make it clear that (a) motion and impulse are propenies of bodies and that therefore they can be found in objects and in our sense organs, but that (b) the light and colors we see are modifications of the soul, which are quite different from the above propenies and of which we also have quite different ideas.