Light is the chaser away of darkness. Shade is the obstruction of light. Primary light is that which falls on objects and causes light and shade. And derived lights are those portions of a body which are illuminated by the primary light. A primary shadow is that side of a body on which the light cannot fall.

Darkness is absence of light. Shadow is diminution of light.

Shadow partakes of the nature of universal matter. All such matters are more powerful in their beginning and grow weaker towards the end, I say at the beginning, whatever their form or condition may be and whether visible or invisible. And it is not from small beginnings that they grow to a great size in time; as it might be a great oak which has a feeble beginning from a small acorn. Yet I may say that the oak is most powerful at its beginning, that is where it springs from the earth, which is where it is largest.

A luminous body will appear more brilliant in proportion as it is surrounded by deeper shadow.

The reason of this is that if you look at the movement of the wateryour eye will not be able to fix on anything, but its action is as that of things seen in your shadow when you are walking; for if the eyeat-tempt to distinguish the nature of the shadow, the wisps of strawor other things contained in it appear of rapid movement and it seems that these are much more swift to flee from the said shadow than the shadow is to proceed.

The beginnings and ends of shadow lie between the light and darkness and may be infinitely diminished and infinitely increased. Shadow is the means by which bodies display their form. The forms of bodies could not be understood in detail but for shadow.