Smith is reading an open book that was shut this morning. At least it certainly seems like the same book he placed closed on his nightstand and opened to read this evening. But, then again, nothing can be both shut and not shut, Smith's book being included among those things that cannot violate G.W. Leibniz's law. So, no matter that common sense dictates that Smith's shut book did not blink out of existence to be instantaneously replaced by an open book, perhaps it is a different book after all.

Very roughly, that is the start of the problem of persistence—an initial worry about how an object can persist through a change in its properties. It is a problem that may seem easily dismissed until we identify its source in some of our basic metaphysical commitments and recognize the costs that accompany any way of addressing it...