For anybody who knows Tim Keller it appears impossible that he, the pastor of Redeemer Presbyterian Church in Manhattan, would ever give up his faith. However, I was watching the film version of Keller's bestselling book, The Reason for God, and was surprised to hear him affirm such a possibility. When asked by one of his non-believing interlocutors whether Keller thought that there might be some convincing arguments against Keller's belief Keller replied by saying that he has two grounds for belief. First, he said, is the rational ground - there are many good reasons to believe that Christianity is true. Second, Keller grounds his faith in religious experience. If both his "rational" ground and his "experiential" ground were shaken then, sure, Keller would give up his belief. Keller remarked that the experiential ground would take longer to soften, but that both, in principle, are defeatable.