"The history of science, like the history of all human ideas, is a history of irresponsible dreams, of obstinacy, and of error. But science is one of the very few human activities — perhaps the only one — in which errors are systematically criticized and fairly often, in time, corrected. This is why we can say that, in science, we often learn from our mistakes, and why we can speak clearly and sensibly about making progress there."

“...non-reproducible single occurrences are of no significance to science.”

“I may illustrate this by two very different examples of human behaviour: that of a man who pushes a child into the water with the intention of drowning it; and that of a man who sacrifices his life in an attempt to save the child. Each of these two cases can be explained with equal ease in Freudian and in Adlerian terms. According to Freud the first man suffered from repression , while the second man had achieved sublimation. According to Adler the first man suffered from feelings of inferiority , and so did the second man . I could not think of any human behaviour which could not be interpreted in terms of either theory. It was precisely this fact — that they always fitted, that they were always confirmed — which in the eyes of their admirers constituted the strongest argument in favour of these theories. It began to dawn on me that this apparent strength was in fact their weakness.”

“From Plato to Karl Marx and beyond, the fundamental problem has always been: who should rule the state?”

“Science must begin with myths, and with the criticism of myths.”

“Karl Popper Institute includes complete bibliography 1925-1999”

“A Skeptical Look at Karl Popper by Martin Gardner”