“Fantasy is the impossible made probable. Science Fiction is the improbable made possible.”
“Science fiction deals with improbable possibilities, fantasy with plausible impossibilities.”
“Probable impossibilities are to be preferred to improbable possibilities.”
“Accordingly, the poet should prefer probable impossibilities to improbable possibilities.”
“Science fiction is the art of the possible not the impossible.”
“With respect to the requirement of art, the probable impossible is always preferable to the improbable possible.”