David Lewis was a contented atheist. He was adamant that he would never be converted. Throughout his career as he discussed topics of religion with other philosophers he realised that he would never convert his opponents either. Despite this, he thought there was great value in mapping out the dialectical geography (as it were) between the atheist and the theist, so as to discover the most attractive reflective equilibria. For someone who published a handful of papers on philosophy of religion Lewis spent a lot of time in correspondence with eminent philosophers of religion such as Bob Adams, Alvin Plantinga, and Peter van Inwagen debating a wide variety of subjects that are central to Christian Philosophy especially. As a result, he indirectly contributed to analytic philosophy of religion, beyond the papers he published on the subject. This is evidenced, for instance, by Plantinga’s discussion of what Plantinga calls Lewis’s Dilemma in his Profiles (Springer, 1985).
In this long and quite technical letter we see Lewis in full flight examining Plantinga’s analyses of counterfactuals of freedom in relation to the existence of God and offering his own views on how we should think about God’s ability to actualise differing sets of counterfactuals of freedom. It has to do, ultimately, with Plantinga’s free will defence of the problem of evil. This letter is, in fact, part of an extended discussion between Lewis and Plantinga that began two decades earlier in 1976. (NB: ‘NoN’ refers to Plantinga’s The Nature of Necessity (Oxford, 1974) and ‘GFE’ refers to Plantinga’s God, Freedom, and Evil (Harper and Row, 1974).)