Posner's first post over at Leiter's is full ot good stuff for a philosophoblogger to philosophoblog about. Let's do it in order. First paragraph:
Brian said I’m an atheist, but the word has two distinct meanings. The first is a person who does not have a sense that there is a God–who, in short, is not a religious person. The second is a person who adheres to the doctrine that there is no God. That is a metaphysical proposition that does not interest me. You cannot convince a religious person that there is no God, because he does not share your premises, for example that only science delivers truths. There is no fruitful debating of God’s existence.
I think someone is an atheist if God (or the properties definitive of God) isn't in their ontology. That's it. The difference between someone who goes around insisting that our best theory of the world doesn't need to quantify over God-properties, and someone whose theory of the world just doesn't quantify of God-properties doesn't establish a difference in the meaning of 'atheist'. The difference between someone who goes around telling anyone who will listen that Jesus is their personal lord and savior and someone who just believes it doesn't establish a difference in the meaning of 'Christian'. There are different kinds of atheists and different kinds of Christians, but 'atheist' and 'Christian' mean just one thing.
Second, the world proves Posner wrong. There is fruitful debating of God's existence. People can and are debated into and out of belief in God. I am quite sure that one can find foremerly religious people who were convinced that there is no God. Posner may be right that most people stick to their prejudices and won't accept a good argument to the contrary if it hits them in the face. But his claim is way too strong. My own change in belief had something to do with reasoning, not just some perturbation of animal spirits.