 The author is grateful to the students in his Fall 2016 seminar on atheism and agnosticism: John Absher, Matthew Fritz, Alžbeta Hájková, Vincent Jacobson, Daniel Linford, Adam Nuske, Bianca Oprea, and Luke Wilson. They contributed in a variety of ways to making this entry much better than it would otherwise have been. The author is also grateful to Jeanine Diller and Jeffery Lowder for very helpful comments.