At each stage...entirely new laws, concepts and generalizations are necessary, requiring inspiration and creativity to just as great a degree as in the previous one.

I have yet to see any problem, however complicated, which, when you looked at it in the right way, did not become still more complicated.

It is a truism that the structure of a society is basically determined by its technology. Not in an absolute sense-there may be totally different cultures using identical tools-but the tools settle the possibilities; you can't have interstellar trade without spaceships. A race limited to a single planet, possessing a high knowledge of mechanics but with its basic machines of industry and war requiring a large capital investment, will inevitably tend toward collectivism under one name or another. Free enterprise needs elbow room.

Give fear no hold on you. Keep sinews loose and senses open, ready at every instant to flow with the rush of action.

In my considered opinion, the profit to be made by permanent settlement in space is nothing less than the survival of industrial civilization, and therefore the survival of nearly the entire human race, along with such amenities as peace, freedom, enough to eat, and the chance to reach a high age in good health.

A fanatic's willingness to kill or be killed in the service of a cause cannot prove the rightness of that cause.

Heaven is not as narrowly literal-minded as hell.