The Fool does not question Lewis' conversion to Christianity, and he is quite overwhelmed with his intellect, imagination, and ability to write fiction. But the Fool doubts that Lewis ever was a convinced and dedicated agnostic or atheist. It is true that while still a young man, he professed to have no religion and maintained that "All religions, that is all mythologies, to give them their proper name, are merely man's own invention - Christ as much as Loki." (C. S. Lewis, A Biography , p. 48) but the tone of his objection to religions seems more the schoolboy realization of religious errors and inconsistencies than that of a mature thinker who has considered the atheist or agnostic positions extensively and sympathetically and who accepts the inevitability of one or the other of both positions. As a youth he had an apparent fascination with elaborate systems of mythology, and his later fiction, the Narnia saga and stories of the planets, is filled with poetic symbols of power and morality. It is a small step from contemplating a deity to bowing before it. In one account of his conversion, he said, "In 1929 I gave in and admitted that God is God." ...
1) Being an Atheist is not limited to being "a mature thinker who has considered the atheist or agnostic positions extensively and sympathetically and who accepts the inevitability of one or the other of both positions".
2) He did "accept the inevitability" of Christianity being just one more mythology, all of which were completely false, precisely as Dawkins' argument that Christians or adherents of any other religions are "atheists about all gods except their own, we are so about one god more".
3) He did "accept the inevitability" of miracles not occurring.
4) He did above all "accept the inevitability" of "God is either evil or impotent or both".
In other words, he was a fairly thoroughgoing atheist.
... Had Lewis been a comfortable atheist or committed agnostic, he would not have had anything to "give in" to.
Unless there was some inconsistency about his atheism which he discovered. For instance, where does logic come from, where does morality come from, where does beauty come from. And he tried an impersonal or not sure if personal or impersonal Hegelian absolute before giving in and admitting the Absolute had to be a personal god.
Note that when he became a Theist in 1929, he waited still another year while still rejecting the Gospel as "yet another myth" before becoming a Christian.
The objection of "the fool" (well named since the fool hath said in his heart there is no god) reminds me of Evangelical reactions to apostates. "If he apostasised he can't have been really saved in the first place". May we wager a guess about Gaunilo II's cultural background?
What is true is that he was not trained or house dressed by the specific modern type of Atheism in which QQ like "where does logic come from, where does morality come from, where does beauty come from?" are pushed off as "scientifically unsound" or fallacies - by people who have a hard time sometimes to see what this argument really means and how one using this argument could find anything really logically objectionable in theirs.
Hans Georg Lundahl
Sts Peter and Paul
*Into the Wardrobe : Mere Christianity: A Review