Kingsley Amis: "That frequently taxes people very much."
Brian Aldiss: "But I am surprised that you put it this way round. I would have thought that you constructed Perelandra for the didactic purpose."
C.S. Lewis: "Yes, everyone thinks that. They are quite wrong."
(From a fascinating discussion between the three a few months before Lewis's death in 1963, published as "Unreal Estates" in the Spectrum IV anthology. As the fiftieth anniversary is coming up, perhaps someone might reprint it in full?)