“If such a thing had happened once, it must surely have happened many times in this galaxy of a hundred billion suns.”

“In this single galaxy of ours there are eighty-seven thousand million suns. [...] In challenging it, you would be like ants attempting to label and classify all the grains of sand in all the deserts of the world. [...] It is a bitter thought, but you must face it. The planets you may one day possess. But the stars are not for man.”

“Those wanderers must have looked on Earth, circling safely in the narrow zone between fire and ice, and must have guessed that it was the favourite of the Sun's children.”

“Floyd could imagine a dozen things that could go wrong; it was little consolation that it was always the thirteenth that actually happened.”

“...science fiction is something that could happen - but usually you wouldn't want it to. Fantasy is something that couldn't happen - though often you only wish that it could.”

“And because, in all the Galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped. And sometimes, dispassionately, they had to weed.”

“Much blood has also been spilled on the carpet in attempts to distinguish between science fiction and fantasy. I have suggested an operational definition: science fiction is something that COULD happen - but usually you wouldn't want it to. Fantasy is something that COULDN'T happen - though often you only wish that it could.”