In his Jewish Review of Books essay that I have been quoting the past few days, Michael Weingrad says provocatively that “Christianity is a fantasy religion,” while “Judaism is a science fiction religion.” From this angle, it’s no accident that several classics of sci fi — Walter Miller’s Canticle for Leibowitz (1959), Philip K. Dick’s Man in the High Castle (1962), Philip José Farmer’s To Your Scattered Bodies Go (1971), Robert Silverberg’s Book of Skulls (1973) — have Jewish characters and themes.

Christianity posits an “other” world, a kingdom of the spirit, where a higher law is in force. And as it happens, this is exactly the mode of thought that gives rise to fantasy as a branch of literature. Fantasy is the kind of fiction that sets aside physical law to obey a law of the writer’s devising. G. K. Chesterton calls this sovereign law “the ethics of elfland.” Fantasy must remain faithful to it, just as physical actuality is faithful to physical law. (Fiction that cheats on the ethics of its own world is lousy fiction.) Obviously, there is going to be overlap between the two legal systems. But fantasy is independent of physical law, “exempt from the conditions,” in Henry James’s words, that usually “drag upon” human experience.

Science fiction is founded upon a different way of thinking. My friend Andrew Fox, author of The Good Humor Man, says it well. “SF deals with extrapolations of theoretically possible developments in technology, the sciences, or society,” he observes, while “fantasy deals with events and phenomena which are not within the realm of the physically possible.”

That’s a great description of Jewish life — “extrapolations of the theoretically possible.” It is absurd to keep kosher, it is not easy or convenient, there is no good nutritional reason to do so, it makes no logical sense, but it is possible. Pretty much the same could be said for circumcision, daily prayer, Shabbat, taharat hamishpaha, studying the rituals of the Temple, or almost any of the 613 commandments that Orthodox Jews are required to obey. Jewish law is not the law of another world.

Even the Kabbalah, which appears magical and other-worldly to outsiders, is firmly rooted in the physically possible. The Sefirot, the ten “spheres” of creation, might seem to imply the existence of ten autonomous spiritual realms, but they are, say the mystical experts, “numerically definable.” They are the source of everything in material creation. When Kabbalists measure the limbs of God, they are certain that the limbs are actually that long. The entire purpose of Kabbalah, first, last, and always, is to renew and refresh the obedience to God’s law.

The Jewish aversion to fantasy arises from the Jewish attachment to physical possibility, the confidence that it is entirely possible to serve God in this world, where it is entirely possible for God to be. To the Jews, however — the crew of Spaceship Israel, the people of the alternate history — science fiction feels just like home.

Update: In the original version, I quietly edited Andrew Fox’s remark. In a note to me, he had referred to science fiction as SF. “San Francisco?” I wondered. So I changed it to what I assumed was the standard abbreviation. Andrew has now written to inform me that my assumption was stupidly mistaken. “The abbreviation most commonly used by those ‘inside the ghetto’ is SF,” he told me. The term sci fi “may not bother folks inside the field as much as it once did. But it is sort of our version of a racial slur, and since I tend toward the old school (my favorite works were all written prior to 1975), my sensitivities may be a bit more sensitive than most.” I’ve revised Andrew’s remark above to reflect its original form.