“The Three Theorems of Psychohistorical Quantitivity:The population under scrutiny is oblivious to the existence of the science of Psychohistory.The time periods dealt with are in the region of 3 generations.The population must be in the billions (±75 billions) for a statistical probability to have a psychohistorical validity.”

“Pyscho-history dealt not with man, but with man-masses. It was the science of mobs; mobs in their billions. It could forecast reactions to stimuli with something of the accuracy that a lesser science could bring to the forecast of a rebound of a billiard ball. The reaction of one man could be forecast by no known mathematics; the reaction of a billion is something else again.”

“The Three Laws of Robotics:1: A robot may not injure a human being or, through inaction, allow a human being to come to harm;2: A robot must obey the orders given it by human beings except where such orders would conflict with the First Law;3: A robot must protect its own existence as long as such protection does not conflict with the First or Second Law;The Zeroth Law: A robot may not harm humanity, or, by inaction, allow humanity to come to harm.”

“There is no merit to discipline under ideal circumstances. I must have it in the face of death or it is worthless.”

“In Hamilton's The Universe Wreckers... it was in that novel that, for the first time, I learned Neptune had a satellite named Triton... It was from The Drums of Tapajos that I first learned there was a Mato Grosso area in the Amazon basin. It was from The Black Star Passes and other stories by John W. Campbell that I first heard of relativity.The pleasure of reading about such things in the dramatic and fascinating form of science fiction gave me a push toward science that was irresistible. It was science fiction that made me want to be a scientist strongly enough to eventually make me one.That is not to say that science fiction stories can be completely trusted as a source of specific knowledge... However, the misguidings of science fiction can be unlearned. Sometimes the unlearning process is not easy, but it is a low price to pay for the gift of fascination over science.”

“A number of years ago, when I was a freshly-appointed instructor, I met, for the first time, a certain eminent historian of science. At the time I could only regard him with tolerant condescension.I was sorry of the man who, it seemed to me, was forced to hover about the edges of science. He was compelled to shiver endlessly in the outskirts, getting only feeble warmth from the distant sun of science- in-progress; while I, just beginning my research, was bathed in the heady liquid heat up at the very center of the glow.In a lifetime of being wrong at many a point, I was never more wrong. It was I, not he, who was wandering in the periphery. It was he, not I, who lived in the blaze.I had fallen victim to the fallacy of the 'growing edge;' the belief that only the very frontier of scientific advance counted; that everything that had been left behind by that advance was faded and dead.But is that true? Because a tree in spring buds and comes greenly into leaf, are those leaves therefore the tree? If the newborn twigs and their leaves were all that existed, they would form a vague halo of green suspended in mid-air, but surely that is not the tree. The leaves, by themselves, are no more than trivial fluttering decoration. It is the trunk and limbs that give the tree its grandeur and the leaves themselves their meaning.There is not a discovery in science, however revolutionary, however sparkling with insight, that does not arise out of what went before. 'If I have seen further than other men,' said Isaac Newton, 'it is because I have stood on the shoulders of giants.”

“Life would be impossible on such a planet. It wouldn't get enough heat and light, and if it rotated there would be total darkness half of every day. There wouldn't be any native inhabitants. You couldn't expect life---which is fundamentally dependent on light---to develop under such extreme conditions of light deprivation. Half of every axial rotation spent in Darkness! No, nothing could exist under conditions like that.”