Hans Halvorson is Professor of Philosophy at Princeton University. He has written extensively on the foundations of quantum physics, with articles appearing in the Journal of Mathematical Physics, the Physical Review, Philosophy of Science, and the British Journal for the Philosophy of Science, among others. He is currently working on applying the tools of category theory to questions in the foundations of mathematics. Halvorson has been the recipient of the Mellon New Directions Fellowship (2007), the Cushing Memorial Prize in the History and Philosophy of Physics (2004), Best Article of the