What is a shadow? Nothing in itself, you might say: a mere local lack of light, in a space that is otherwise lit up. Light, which allows us to see and know the world, is the normal precondition for picturing things. Cast shadows may help us interpret a picture by indicating where light comes from and where objects stand, but if you survey art history, you find the majority of painters giving them minor parts at most. A minority, however, turns these assumptions upside down, treating shadow as the preexistent condition and light as its shock interruption.