Jim Slagle, at Agent Intellect, wrote his master's thesis on the Argument from Reason for the University of Louvain, and in the process convinced me to change my mind about one aspect of the argument. At first I thought that Anscombe had shown that Lewis was misusing the term "irrational", in the first edition of Miracles, in speaking of physical causes, but in fact Lewis was using a different, but perfectly acceptable sense of the word "irrational." Lewis in fact distinguishes the two senses of the word "irrational in The Abolition of Man." Lewis did adopt the irrational-non-rational distinction when he revised the third chapter of Miracles, but, strictly speaking, he need not have done so.
In this post, he presents what he considers to be Chesterton's version of the AFR.