For each human being there is an optimum ratio between change and stasis. Too little change, he grows bored. Too little stability, he panics and loses his ability to adapt. One who marries six times in ten years won't change jobs. One who moves often to serve his company will maintain a stable marriage. A woman chained to one home and family may redecorate frantically or take a lover or go to many costume parties.

Species evolve to meet the environment. An intelligent species changes the environment to suit itself. As soon as a species becomes intelligent, it should stop evolving.

In the world of words the imagination is one of the forces of nature.

As for AIDS, it's a plague. We are human, we get plagues. They come along every so often, kill off two thirds of the population; in the next generation it's a quarter; after that it's a childhood disease.

It is a cardinal sin to bore the reader.

And every friend I've got has been writing Mars stories. It was pretty clear I'd never catch up.

One mark of a good officer, he remembered, was the ability to make quick decisions. If they happen to be right, so much the better.