Karl Popper Quotes

I have no faith in precision: ...simplicity and clarity are values in themselves, but not... [of] precision or exactness...

Piecemeal social engineering resembles physical engineering in regarding the ends as beyond the province of technology. (All that technology may say about ends is whether they are compatible with each other or realizable.)

One of the ideas I had discussed in The Poverty of Historicism was the influence of a prediction upon the event predicted. I had called this the "Oedipus effect", because the oracle played a most important role in the sequence of events which led to the fulfilment of its prophecy. ... For a time I thought that the existence of the Oedipus effect distinguished the social from the natural sciences. But in biology, too—even in molecular biology—expectations often play a role in bringing about what has been expected.

A theory which is not refutable by any conceivable event is nonscientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

Science is not a system of certain, or well established, statements; nor is it a statement which steadily advances towards state of finality. Our science is not knowledge (epistēmē): it can newer claim to have attained truth, or even substitute for it, such as probability. . . . We do not know; we can only guess.

True ignorance is not the absence of knowledge, but the refusal to acquire it.

Darwinism is not a testable scientific theory, but a metaphysical research program.

... 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.

Besides, we should never attempt to balance anybody's misery against somebody else's happiness.

Most of us, it seems, have a strong inclination to accept the peculiarities of our social environment as if they were ‘natural’.

I assert
(1) There is no method of discovering a scientific theory.
(2) There is no method of ascertaining the truth [i.e., verification] of a scientific hypothesis...
(3) There is no method of ascertaining whether a hypothesis is 'probable', in the sense of the probability calculus.

The doctrine that there is as much science in a subject as... mathematics in it, or as much... measurement or 'precision' in it, rests upon... misunderstanding.

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.

the alleged clash between freedom and security, that is, a security guaranteed by the state, turns out to be a chimera. For there is no freedom if it is not secured by the state; and conversely, only a state which is controlled by free citizens can offer them any reasonable security at all.)

We all remember how many religious wars were fought for a religion of love and gentleness; how many bodies were burned alive with the genuinely kind intention of saving souls from the eternal fire of hell. Only if we give up our authoritarian attitude in the realm of opinion, only if we establish the attitude of give and take, of readiness to learn from other people, can we hope to control acts of violence inspired by piety and duty.