Allen Tate

According to its doctors, my one intransigent desire is to have been a Confederate general, and because I could not or would not become anything else, I set up for poet and beg an to invent fictions about the personal ambitions that my society has no use for.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.