PETER VAN INWAGEN is John Cardinal O'Hara Professor of Philosophy at the University of Notre Dame. He is the author of The Problem of Evil (2006), Ontology, Identity, and Modality (2001), God, Knowledge, and Mystery: Essays in Philosophical Theology (1995), Metaphysics (1993), Material Beings (1990), and An Essay on Free Will (1983).

DEAN W. ZIMMERMAN is Associate Professor of Philosophy at Rutgers University. He has published articles on metaphysics in a number of journals and collections, including The American Philosophical Quarterly, Analysis, The Australasian Journal of Philosophy, Mind, The Monist, Noûs, The Philosophical Review, and Philosophy and Phenomenological Research. He is also editor of the Oxford Studies in Metaphysics series.