From page 94:
If Homer had not lived, eventually someone else would have written a poem about revenge, gods, and a war over a beautiful woman. Yet once the Iliad is in existence, it becomes hard to determine whether subsequent authors of works on these themes are copying the Iliad or copying life.
Lots of good stuff in here, by the way. Their discussion of the different sorts of uncopyrightable ideas in fiction and nonfiction (from which the above is taken) has cleared up a number of issues that had been troubling me, and I find myself flagging a passage for later reference every twenty pages or so.