About the fifth century BC, three civilizations independently and simultaneously began to philosophize about nothing: China (chapter 3), India (chapters 4 and 5), and Greece (chapters 6-10). They had previously focused on what is the case. Light poured on nature, architecture, and society. But then, in a cross-civilizational black-out, emerged disparate nay-sayers who shifted attention to what is not the case. Behold, the holes in a sponge are absences of sponge! Holes are what make the sponge useful for absorbing liquid. The sponge can exist without the holes. But the holes cannot "exist" without the sponge. They are parasites that depend on their host. Yet the two get along well. Without holes, there would not be so many sponges in your house. Your shadow is a more complex parasite. It is a hole you bore into the light. Your shadow depends on both you and the light. You and light are rather mysterious. Your shadow partakes of both mysteries. .