Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living.

You don't believe in organized religion, yet a major theme in so many of your works seems to be a quest for God.

The difference between machines and human beings is that human beings can be reproduced by unskilled labour.

Don't mess up the environment until you're quite sure what you're doing.

Though the man-apes often fought and wrestled one another, their disputes very seldom resulted in serious injuries. Having no claws or fighting canine teeth, and being well protected by hair, they could not inflict much harm on one another. In any event, they had little surplus energy for such unproductive behavior; snarling and threatening was a much more efficient way of asserting their points of view.

The crossing of space ... may do much to turn men's minds outwards and away from their present tribal squabbles. In this sense, the rocket, far from being one of the destroyers of civilisation, may provide the safety-value that is needed to preserve it.

Sometimes a decision has to be made by a single individual, who has the authority to enforce it. That's why you need a captain. You can't run a ship by a committee-at least not all the time.