About six months ago, on the last day of a library book sale when everything was going for a song, I randomly bought a couple dozen dog-eared sci-fi paperbacks. A few weeks ago I pulled one out and discovered, on actually looking at it, that it was about an alien invasion of medieval England.

I took this as a bad sign. Oh, I was game to see an alien spaceship interrupt an English army readying to attack France, but I wasn’t interested in cheap anti-medieval stereotypes or scorn. That the book was titled The High Crusade only seemed another warning. Still, I went ahead and read the novel. I’d paid for it, after all, even if only a song.

And it turned out to be the best book I’d read in months. It clashed the ornate, highly religious, and relatively backward culture of fourteenth-century England against the advanced, utilitarian, and completely secular alien culture so typically imagined. The author played out the war in surprising ways, and he treated the medieval culture of his characters with good humor and even something like respect.

I had thought it far more likely the author would make the clash a story of how poor, benighted, God-believing primitives were raised up by the light of science and secularism because, well, I assumed that would be his own worldview. I didn’t know anything about the author, and in fact I still don’t. But until I see otherwise, I always assume the sci-fi authors I read are secularists who have no use for religion. It may not be the only worldview behind science fiction, but it is the dominant one. It is certainly the one I most often encounter.

My worldview is Christian, and I’ve grown attuned to the secular and evolutionistic undertones common in science  fiction. And yet I enjoy sci-fi. Sometimes the contrary viewpoint annoys me, and sometimes it makes the story hard for me to buy; I can’t really get behind the idea that highly-evolved prairie dogs will rise to inherit the earth, even in science fiction. Often enough, though, the author’s underlying worldview makes no difference to what is in the story, though I suspect it made a difference in what was left out. Not every story comes armed with a clear statement, or even an implicit stand, on existential questions.

There is a third way a secular worldview shows itself, and the way I most often experience it. The worldview reveals itself in a way essentially tangential to the story – the by-the-way explanation that attributes a whole species’ nature to its environment, the implicit assumption that the difference between humanity and animals is one of degree and not kind, that of course advanced cultures don’t believe in God …

The ultimate effect of these moments on the story can be very minor, and the effect on the reader (or watcher) even less. These ideas, once they are recognized as ideas, have little influence; it’s when they are unreflectively absorbed as attitudes that they are most powerful. Sci-fi is full of ideas – that’s why I love it – and they can sound credible to the point of being scientific. But the canny sci-fi reader knows that that is all part of the fun, that everybody is always guessing.

This is why, although I recognize the secular worldview that undergirds much of science fiction, I don’t reject the genre, or even all its provably secular works. To encounter a bad idea is not to believe it, and tangents usually don’t derail whole stories. Besides, as I learned with The High Crusades, our assumptions – even those based on past experiences – can always be wrong.