"[8] (Of course, Narnia was fantasy rather than science fiction, but Mort is noting the similarities in style and execution of the story.)
Other early authors identified by Mort as being influences upon the development of Christian science fiction include J. R. R. Tolkien, George MacDonald and Charles Williams.
[8] (Although, again, these writers worked in fantasy, their influence on Christian science fiction is clear, Mort argues.)
[11] For example, the first of these difficulties has been identified by Pierce as a problem with some of R. A. Lafferty's work, who "is uncomfortable with the idea of even biological evolution";[3] while Tom Doyle notes the predictability of the Christian apocalyptic novel, due, he argues, to the genre following "a particular interpretation of biblical prophecy".
[12] These difficulties raise concerns regarding genre boundaries: while Christian science fiction has been identified as a specific market into which stories can be sold,[13] Doyle has questioned whether or not books that are, at times, classified in this subgenre truly fit.