Swanwick on the difference between fantasy and science fiction
The essential difference, it seemed to me, was that science fiction occurs in a knowable universe. Human beings may or may not be smart enough to figure out the rules, but a strong enough intelligence could. But the fantasy universe is ultimately unknowable. At its heart lies mystery. And this mystery is essentially religious in nature. That’s one of the charms of fantasy, the ability to play with spiritual ideas without the moral pitfalls of doing so in the real world. It is also, incidentally, why fantasy worlds that start from a set of rules for magic will so often feel a lot like science fiction. What makes magic fantastic is that it punches a hole in our perception of what is and is not possible, that it takes us beyond the realm of mere rules.
I found this to be an incredibly interesting and insightful comment as a lifelong reader of science fiction and fantasy. It also shows some of the mind that has made him one of my favorite authors.