HOW THERE ARE 2 KINDS OF LIGHT, ONE SEPARABLE FROM, AND THE OTHER
INSEPARABLE FROM BODIES.

Of the various kinds of light (126, 127).

Separate light is that which falls upon the body. Inseparable light
is the side of the body that is illuminated by that light. One is
called primary, the other derived. And, in the same way there are
two kinds of shadow:--One primary and the other derived. The primary
is that which is inseparable from the body, the derived is that
which proceeds from the body conveying to the surface of the wall
the form of the body causing it.