Space can be mapped and crossed and occupied without definable limit; but it can never be conquered.

The goal of the future is full unemployment, so we can play. That's why we have to destroy the present politico-economic system.

The choice, as Wells once said, is the Universe-or nothing. . . . The challenge of the great spaces between the worlds is a stupendous one; but if we fail to meet it, the story of our race will be drawing to its close. Humanity will have turned its back upon the still untrodden heights and will be descending again the long slope that stretches, across a thousand million years of time, down to the shores of the primeval sea.

It was one thing to have guessed it, another to have had that guess confirmed beyond possibility of refutation.

Every revolutionary idea seems to evoke three stages of reaction. They may be summed up by the phrases: 1- It's completely impossible. 2- It's possible, but it's not worth doing. 3- I said it was a good idea all along.

As three laws were good enough for Newton, I have modestly decided to stop there.

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.