Overhead, without any fuss, the stars were going out.

As his body became more and more defenseless, so his means of offense became steadily more frightful.

Good morning, Dr. Chandra. This is Hal. I am ready for my first lesson.

I suspect that religion is a necessary evil in the childhood of our particular species. And that's one of the interesting things about contact with other intelligences: we could see what role, if any, religion plays in their development. I think that religion may be some random by-product of mammalian reproduction. If that's true, would non-mammalian aliens have a religion?

Anything that is theoretically possible will be achieved in practice, no matter what the technical difficulties are, if it is desired greatly enough.

We over estimate technology in the short term and under estimate technology in the long term.

I'm sure we would not have had men on the Moon if it had not been for Wells and Verne and the people who write about this and made people think about it. I'm rather proud of the fact that I know several astronauts who became astronauts through reading my books.