Excessive interest in pathological behavior was itself pathological

The choice, as Wells once said, is the Universe-or nothing. . . . The challenge of the great spaces between the worlds is a stupendous one; but if we fail to meet it, the story of our race will be drawing to its close. Humanity will have turned its back upon the still untrodden heights and will be descending again the long slope that stretches, across a thousand million years of time, down to the shores of the primeval sea.

When one has to ask, "Am I really in love?" the answer is always "No".

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

Across the gulf of centuries, the blind smile of Homer is turned upon our age. Along the echoing corridors of time, the roar of the rockets merges now with the creak of the wind-taut rigging. For somewhere in the world today, still unconscious of his destiny, walks the boy who will be the first Odysseus of the Age of Space.

There's a passage about 'rivers of molten rock that wound their way... until they cooled and lay like twisted dragon-shapes vomited from the tormented earth.' That's a perfect description: how did Tolkien know, a quarter century before anyone ever saw a picture of Io? Talk about Nature imitating Art.

Any technology distinguishable from magic is insufficiently advanced.