"... the attempt to make heaven on earth invariably produces hell. It leads to intolerance. It leads to religious wars, and to the saving of souls through the inquisition. And it is, I believe, based on a complete misunderstanding of our moral duties. It is our duty to help those who need help; but it cannot be our duty to make others happy, since this does not depend on us, and since it would only too often mean intruding on the privacy of those towards whom we have such amiable intentions."

“...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”