“Scientific theories can always be improved and are improved. That is one of the glories of science. It is the authoritarian view of the Universe that is frozen in stone and cannot be changed, so that once it is wrong, it is wrong forever.”

Rediscovering Lost Values http://mlk-kpp01.stanford.edu/index.php/kingpapers/article/rediscovering_lost_values/, Sermon delivered at Detroit's Second Baptist Church (28 February 1954)
1950s
Context: We have adopted in the modern world a sort of a relativistic ethic... Most people can't stand up for their convictions, because the majority of people might not be doing it. See, everybody's not doing it, so it must be wrong. And since everybody is doing it, it must be right. So a sort of numerical interpretation of what's right. But I'm here to say to you this morning that some things are right and some things are wrong. Eternally so, absolutely so. It's wrong to hate. It always has been wrong and it always will be wrong. It's wrong in America, it's wrong in Germany, it's wrong in Russia, it's wrong in China. It was wrong in 2000 B. C., and it's wrong in 1954 A. D. It always has been wrong, and it always will be wrong. It's wrong to throw our lives away in riotous living. No matter if everybody in Detroit is doing it, it's wrong. It always will be wrong, and it always has been wrong. It's wrong in every age and it's wrong in every nation. Some things are right and some things are wrong, no matter if everybody is doing the contrary. Some things in this universe are absolute. The God of the universe has made it so. And so long as we adopt this relative attitude toward right and wrong, we're revolting against the very laws of God himself. [... ] That attitude is destroying the soul of our culture! It's destroying our nation! The thing that we need in the world today is a group of men and women who will stand up for right and to be opposed to wrong, wherever it is. A group of people who have come to see that some things are wrong, whether they're never caught up with. And some things are right, whether nobody sees you doing them or not.

Epigrams on Programming, 1982

Source: How Maps Work: Representation, Visualization, and Design (1995), p. 9

The Scientist As Rebel (2006)

Academy of Achievement interview (1991)
Context: Reason alone will not serve. Intuition alone can be improved by reason, but reason alone without intuition can easily lead the wrong way. They both are necessary. The way I like to put it is that when I have an intuition about something, I send it over to the reason department. Then after I've checked it out in the reason department, I send it back to the intuition department to make sure that it's still all right. That's how my mind works, and that's how I work. That's why I think that there is both an art and a science to what we do. The art of science is as important as so-called technical science. You need both. It's this combination that must be recognized and acknowledged and valued.

Winston Churchill (June 23, 1925), His complete speeches, 1897–1963, edited by Robert Rhodes James, Chelsea House ed., vol. 4 (1922–1928), p. 3706. During a debate with Philip Snowden, 1st Viscount Snowden.
Often misquoted as: To improve is to change, to be perfect is to change often.
Early career years (1898–1929)

Time Must Have a Stop (1944)

Source: The Martyrdom of Man (1872), Chapter IV, "Intellect"

describing his discoveries in Density functional theory, December 29, 1995, in an interview with [István Hargittai, Magdolna Hargittai, Candid science: conversations with famous chemists, Volume 1 of Candid science, Imperial College Press, 2000, 1860942288, 180]