"You know, we’re not used to secrecy up here. It’s not encouraged. We all have to work together to keep alive. Secrecy is corrosive, Professor, bad for morale."

"He says that even a god cannot conquer time, but nine hundred years should be enough for anybody."

"Kolya believed that the Mongols’ expansion was pathological. It was a ghastly spiral of positive feedback, born of Genghis Khan’s unquestioned military genius and fueled by easy conquests, a plague of insanity and destruction that had spread across most of the known world."

"Eumenes showed little taste for elaborate protocols; he was far too intelligent for that."

"We have no idea what waits for us out there. We did not choose this situation, and whatever manner of creature or accident has stranded us here did not take much notice of our welfare. I would say nice moral questions are beside the point, and that pragmatism is the order of the day."

"Grove was inclined to allow the request. “I can’t see how we can be harmed by allowing the destruction of what I don’t understand anyhow,” he said dryly. “And besides—you say it is your duty, Warrant Officer. I respect that. Time and space may flow like toffee, but duty endures.”"

"The false logic involved is: “We exist; therefore something—call it X—created us.” Once this assumption is made, the properties of the hypothetical X can be fantasied in an unlimited number of ways. But the entire process is obviously fallacious; for by the same logic something must have created X—and so on. We are immediately involved in an infinite regress, which can have no meaning in the real universe."

"Christine would surely be talking, even if she had only an ape as audience. To her, any silence was as great a challenge as a blank canvas; it had to be filled with the sound of her own voice."

"The idea of death was utterly incongruous—as it is to all men until the final second."

"It is hardly necessary for me to say that I do not believe in the supernatural; everything that happened has a perfectly rational explanation, obvious to any man with the slightest knowledge of psychology."

"There was nothing like a museum for calming the mind, for putting the problems of everyday life in their true perspective. Here, surrounded by the infinite variety and wonder of Nature, he was reminded of truths he had forgotten. He was only one of a million million creatures that shared this planet Earth. The entire human race, with its hopes and fears, its triumphs and its follies, might be no more than an incident in the history of the world."

"Why should men travel, he asked himself bitterly, across the gulf of stars at such expense and risk—merely to land on a spinning slag heap? For the same reason, he knew, that they had once struggled to reach Everest and the Poles and the far places of the Earth—for the excitement of the body that was adventure, and the more enduring excitement of the mind that was discovery."

"This sounded promising, and my coefficient of cupidity jumped several points."

"For what is life but organized energy?"

"“You’re a gang of robbers,” he said once. “You’re seeing how quickly you can loot this planet of its resources, and you don’t give a damn about the next generation.” “And what,” answered McKenzie, not very originally, “has the next generation ever done for us?”"

"There may be a moral here. For the life of me I can't find it."

"Captain Saunders, who came from Dallas and had no intention of being impressed by any prince, found himself unexpectedly moved by the wide, sad eyes. There were eyes that had seen too many receptions and parades, that had had to watch countless totally uninteresting things, that had never been allowed to stray far from the carefully planned official routes. Looking at that proud but weary face, Captain Saunders glimpsed for the first time the ultimate loneliness of royalty."

"Like the atom bomb, it arose out of equally academic research. Never, gentlemen, underestimate science. I doubt if there is a single field of study so theoretical, so remote from what is laughingly called everyday life, that it may not one day produce something that will shake the world."

"“Censorship does raise some very difficult problems, doesn’t it? I’ve always argued that there’s an inverse correlation between a country’s degree of civilisation and the restraints it puts on its press.” A New English voice from the back of the room cut in: “On that argument, Paris is a more civilised place than Boston.” “Precisely,” answered Purvis. For once, he waited for a reply. “OK,” said the New England voice mildly. “I’m not arguing. I just wanted to check.”"

"History, it has been said, never repeats itself but historical situations recur."

"Great art and domestic bliss are mutually incompatible. Sooner or later, you'll have to make your choice."

"Though I've often made fun of the scientists, they've freed us forever from the stagnation that was overtaking your race."

"You won’t be an artist if you live a thousand years. You’re merely an expert, and you know it. Those who can—do, those who can’t—criticise."

"Yet it was the impression that the unknown master has set out to create, Phoenix-like, from the dying embers of a great legend. He had captured, and held for all future ages to see, that beauty whose service is the purpose of life, and it sole justification."

"It was good to be alive; it was better to be young; it was best of all to be in love."

"There are some things that no amount of pure intelligence can anticipate, but which can only be learned by bitter experience."

"It was very pleasant to be loved, but it had its disadvantages if one stopped to look beyond the immediate moment. For a fleeting instant Yradne wondered if she had been fair to Jon, to Brant—even to herself. One day the decision would have to be made; it could not be postponed forever. Yet she could not for the life of her decide which of the boys she liked the better; and she did not know if she loved either. No one had ever told her, and she had not yet discovered, that when one has to ask “Am I really in love?” the answer is always “No”."

"The person one loves never really exists, but is a projection focused through the lens of the mind onto whatever screen it fits with least distortion."

"The future is built on the rubble of the past; wisdom lies in facing that fact, not in fighting against it."

"I doubt if such a word exists, and if it does, it shouldn’t."

"Purvis looked at him as though seeing something that had no right to be around in a world that had invented penicillin."

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

"The extremists in his movement had discredited themselves thoroughly, and it would be a long time before the world heard of them again."

"“Very ingenious, like all your theories,” said Stormgren. “I wish you’d give them Opus numbers so that I could keep up with them. The objections to this one—”"

"Now there are some forms of apparel that may be worn or discarded as the fancy pleases with no other ill effects than a possible loss of social prestige. But spacesuits are not among them."

"A single neutron begins the chain-reaction that in an instant can destroy a million lives and the toil of generations. Equally insignificant and unimportant are the trigger-events which can sometimes change a man’s course of action and so alter the whole pattern of his future."

"It is surprising how long it takes to do a simple addition when your life depends on the answer."

"News that is sufficiently bad somehow carries its own guarantee of truth. Only good reports need confirmation."

"He was suddenly struck by an idea so brilliant that he was quite sure it could not possibly work."

"The centre of gravity of a parallelogram is the point of intersection of its diagonals."

"The centre of gravity of any parallelogram lies on the straight line joining the middle points of opposite sides."

"Two magnitudes whether commensurable or incommensurable, balance at distances reciprocally proportional to the magnitudes."

"If two equal weights have not the same centre of gravity, the centre of gravity of both taken together is at the middle point of the line joining their centres of gravity."

"Equal weights at equal distances are in equilibrium and equal weights at unequal distances are not in equilibrium but incline towards the weight which is at the greater distance."

"Those who claim to discover everything but produce no proofs of the same may be confuted as having actually pretended to discover the impossible."

"How many theorems in geometry which have seemed at first impracticable are in time successfully worked out!"