There are some ideas so stupid that only intellectuals can believe in them, particularly left-wing intellectuals.

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.

Heaven is not as narrowly literal-minded as hell.

The fish that first ventured ashore had considerable practical problems.

My knowledge of the human psyche is as yet imperfect. Certain areas won't yield to computation.

Colonization means potential immortality for the human genus. Man's safety on Earth was never great, and it dwindles hourly. Disarmament, even world government, will not guarantee survival in an age when population presses natural resources to the limit and when the knowledge of how to work mischief on a planetary scale is ever more widely diffused among peoples who may grow ever more desperate.

What five books would I like to be remembered for? Well... Tau Zero, I like that one especially. It was somewhat of a tour de force, and I think it got across what I was trying for.