Once upon a time, I made an unfortunate attempt to label the kind of thing Poul [Anderson] writes as “hard copy”—work so deeply felt and so carefully crafted that it looks solid no matter from what angle you view it—and I asked for more of the same from other people. Everyone instantly assumed that what I was talking about was sf in which the science was correct, and thus inadvertently was born our present usage of “hard science fiction.”
From James Blish The Tale That Wags the God
The distinction between “hard” and “soft” is useful but I’ve seen various debates in the Sci-Fi community over whether or not it’s contrived. Nice to know it was all a fluke! Language is funny this way.