Earlier versions of this paper were presented at the philosophy departments in Duke, Stirling, Edibnburgh, Washington University in St. Louis, Rutgers, and Vermont; at the epistemology group in the Van Leer Institute in Jerusalem; in a conference at the university of Graz; and at the Hebrew University Institute of Advanced Studies. I thank the participants—and especially Wilfried Hinsch, my commentator at Graz—for the valuable discussion. I also received helpful comments from Hagit Benbaji, Matthew Braddock, Terence Cuneo, Antony Duff, Yuval Eylon, Adil Ahmad Haque, Simon Hope, Arthur Kuflik, Ambrose Lee, Ofer Malcai, Mark Moyer, Arik Pelman, Stephen Perry, Christian Piller, Jim Pryor, Joseph Raz, Ben Saunders, Walter Sinnott-Armstrong, Holly Smith, Roy Sorensen, Levi Spectre, Gopal Sreenivasan, Larry Temkin, Sergio Tenenbaum, Michael Thompson, Bas van der Vossen, and Matt Weiner. Also, this research was supported by the Israel Science Foundation (grant no. 136/09).