And because, in all the Galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped. And sometimes, dispassionately, they had to weed.

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

The numbers of distinct human societies or nations, when our race is twice its present age, may be far greater than the total number of all the men who have ever lived up to the present time.

I can never look now at the Milky Way without wondering from which of those banked clouds of stars the emissaries are coming. If you will pardon so commonplace a simile, we have set off the fire alarm and have nothing to do but to wait. I do not think we will have to wait for long.

We have to abandon the idea that schooling is something restricted to youth. How can it be, in a world where half the things a man knows at 20 are no longer true at 40 - and half the things he knows at 40 hadn't been discovered when he was 20?

There were some things that only time could cure. Evil men could be destroyed, but nothing could be done with good men who were deluded.

Religion is a by-product of fear. For much of human history it may have been a necessary evil, but why was it more evil than necessary? Isn’t killing people in the name of god a pretty good definition of insanity?