Prior to Flew, major apologies for atheism were those of Enlightenment thinkers (David Hume, Arthur Schopenhauer, Ludwig Feuerbach, and Friedrich Nietzsche). Major philosophers of Flew's generation who were atheists: W. V. O. Quine and Gilbert Ryle. But none took the step of developing book-length arguments to support their personal beliefs. In later years, atheist philosophers who critically examined and rejected the traditional arguments for God's existence: Paul Edwards, Wallace Matson, Kai Nielsen, Paul Kurtz, J. L. Mackie, Richard Gale, Michael Martin. But their works did not change the agenda and framework of discussion the way Flew's innovative publications did.