(This is another item from my drafts folder that was never published. I think I wrote this in early 2006. I have fixed/added some links and made some edits.)
The journal Philosophia Christi and perhaps, by extension, Biola University, have made a big deal of Antony Flew's conversion from atheism to theism in the article, "Atheist Becomes Theist." See:
When Flew did call himself an atheist, he made it very clear that he always considered himself a so-called 'negative' atheist. In his terminology, he lacked belief in God, but he never held the positive belief that God does not exist. In this sense, Flew's "presumption of atheism" could be renamed the "presumption of agnosticism" (as at least one Christian apologist has pointed out). Furthermore, to the best of my knowledge, Flew never accepted any of the arguments for the nonexistence of God. (If anyone knows of any evidence to the contrary, please let me know and I will accordingly issue an update to this post.)
Why does this matter? Because many theists, including several of the Christian philosophers associated with Philosophia Christi (Craig [see here], Moreland, Geivett, Copan [see here], et al) have always criticized this definition of atheism as revisionist. Whenever someone would say in a debate that atheism is merely the lack of theistic belief, the Philosophia Christi philosophers would say that atheism is properly defined as what Flew called 'positive' atheism, viz, the belief that God does not exist. According to these philosophers, individuals who are merely 'negative' atheists are not atheists at all.
So it seems there is tension here, if not an outright contradiction, between what some Christian philosophers have typically said about the definition of atheism, and their attribution of atheism to Antony Flew.
Either Flew was an atheist and so-called 'negative' atheism is a form of atheism after all, or atheism must be defined as the positive belief that there is no God and hence Flew was never an atheist (in that sense) and hence theists should not refer to Flew as a former atheist.
In order to avoid any misunderstandings, I want to emphasize a couple of points. First, I am not objecting to the Philosophia Christi philosophers' insistence that atheism be defined as the positive belief there is no God. In fact, I pretty much agree with them. Second, regardless of how we label Flew's pre-Deism position (e.g., 'atheist', 'negative atheist', or agnostic), nothing I have written is any way meant to deny the fact that Flew apparently moved from naturalism to supernaturalism (i.e., deism). All I have claimed is that there seems to be a tension between how certain Christian philosophers have defined atheism, on the one hand, and how they have labeled Flew's beliefs prior to his conversion to deism.