The greatest weapons in the conquest of knowledge are an understanding mind and the inexorable curiosity that drives it on.

The fundamentalists deny that evolution has taken place; they deny that the earth and the universe as a whole are more than a few thousand years old, and so on. There is ample scientific evidence that the fundamentalists are wrong in these matters, and that their notions of cosmogony have about as much basis in fact as the Tooth Fairy has.

And above all things, never think that you're not good enough yourself. A man should never think that. My belief is that in life people will take you at your own reckoning.

To introduce something altogether new would mean to begin all over, to become ignorant again, and to run the old, old risk of failing to learn.

Democracy cannot survive overpopulation.

If you're born in a cubicle and grow up in a corridor, and work in a cell, and vacation in a crowded sun-room, then coming up into the open with nothing but sky over you might just give you a nervous breakdown.

All roads lead to Trantor, says the old proverb, and that is where all stars end.