Karl Popper Quotes

Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society, then the tolerant will be destroyed, and tolerance with them. We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.

I remained a socialist for several years, even after my rejection of Marxism; and if there could be such a thing as socialism combined with individual liberty, I would be a socialist still. For nothing could be better than living a modest, simple, and free life in an egalitarian society.

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

Whenever a theory appears to you as the only possible one, take this as a sign that you have neither understood the theory nor the problem which it was intended to solve.

The growth of knowledge depends entirely upon disagreement.

Every intellectual has a very special responsibility. He has the privilege and the opportunity of studying. In return, he owes it to his fellow men (or 'to society') to represent the results of his study as simply, clearly and modestly as he can. The worst thing that intellectuals can do - the cardinal sin - is to try to set themselves up as great prophets vis-à-vis their fellow men and to impress them with puzzling philosophies. Anyone who cannot speak simply and clearly should say nothing and continue to work until he can do so.

No rational argument will have a rational effect on a man who does not want to adopt a rational attitude.

In so far as a scientific statement speaks about reality, it must be falsifiable; and in so far as it is not falsifiable, it does not speak about reality.

The question is not how to get good people to rule; THE QUESTION IS: HOW TO STOP THE POWERFUL from doing as much damage as they can to us.

If you can't say it simply and clearly, keep quiet, and keep working on it till you can.

The best thing that can happen to a human being us to find a problem, to fall in love with that problem, and to live trying to solve that problem, unless another problem even more lovable appears.

The war of ideas is a Greek invention. It is one of the most important inventions ever made. Indeed, the possibility of fighting with with words and ideas instead of fighting with swords is the very basis of our civilization, and especially of all its legal and parliamentary institutions.

Ignorance is not a simple lack of knowledge but an active aversion to knowledge, the refusal to know, issuing from cowardice, pride, or laziness of mind.

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

When we enter a new situation in life and are confronted by a new person, we bring with us the prejudices of the past and our previous experiences of people. These prejudices we project upon the new person. Indeed, getting to know a person is largely a matter of withdrawing projections; of dispelling the smoke screen of what we imagine he is like and replacing it with the reality of what he is actually like.

I may be wrong and you may be right, and by an effort, we may get nearer to the truth

I think that there is only one way to science - or to philosophy, for that matter: to meet a problem, to see its beauty and fall in love with it; to get married to it and to live with it happily, till death do ye part - unless you should meet another and even more fascinating problem or unless, indeed, you should obtain a solution. But even if you do obtain a solution, you may then discover, to your delight, the existence of a whole family of enchanting, though perhaps difficult, problem children, for whose welfare you may work, with a purpose, to the end of your days.

The attempt to make heaven on earth invariably produces hell.

We do not choose political freedom because it promises us this or that. We choose it because it makes possible the only dignified form of human coexistence, the only form in which we can be fully responsible for ourselves. Whether we realize its possibilities depends on all kinds of things — and above all on ourselves.

Evolution is not a fact. Evolution doesn't even qualify as a theory or as a hypothesis. It is a metaphysical research program, and it is not really testable science.

Those who promise us paradise on earth never produced anything but a hell.

Our aim as scientists is objective truth; more truth, more interesting truth, more intelligible truth. We cannot reasonably aim at certainty. Once we realize that human knowledge is fallible, we realize also that we can never be completely certain that we have not made a mistake.

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.

It is the rule which says that the other rules of scientific procedure must be designed in such a way that they do not protect any statement in science against falsification.

Astrologers were greatly impressed, and misled, by what they believed to be confirming evidence-so much so that they were quite unimpressed by any unfavorable evidence. Moreover, by making their interpretations and prophecies sufficiently vague they were able to explain away anything that might have been a refutation of the theory had the theory and the prophecies been more precise. In order to escape falsification they destroyed the testability of their theory. It is a typical soothsayer's trick to predict things so vaguely that the predictions can hardly fail: that they become irrefutable.

Nature consists of facts and of regularities, and is in itself neither moral nor immoral. It is we who impose our standards upon nature, and who in this way introduce morals into the natural world, in spite the fact that we are part of this world. We are products of nature, but nature has made us together with our power of altering the world, of foreseeing and of planning for the future, and of making far-reaching decisions for which we are morally responsible. Yet, responsibility, decisions, enter the world of nature only with us

The game of science is, in principle, without end. He who decides one day that scientific statements do not call for any further test, and that they can be regarded as finally verified, retires from the game.

The only way to test a hypothesis is to look for all the information that disagrees with it.

For myself, I am interested in science and in philosophy only because I want to learn something about the riddle of the world in which we live, and the riddle of man's knowledge of that world. And I believe that only a revival of interest in these riddles can save the sciences and philosophy from an obscurantist faith in the expert's special skill and in his personal knowledge and authority.

We have the right not to tolerate the intolerant. We should tolerate even them whenever we can do so without running a great risk; but the risk may become so great that we cannot allow ourselves the luxury.

Optimism is a duty. The future is open. It is not predetermined. No one can predict it, except by chance. We all contribute to determining it by what we do. We are all equally responsible for its success.

The true Enlightenment thinker, the true rationalist, never wants to talk anyone into anything. No, he does not even want to convince; all the time he is aware that he may be wrong. Above all, he values the intellectual independence of others too highly to want to convince them in important matters. He would much rather invite contradiction, preferably in the form of rational and disciplined criticism. He seeks not to convince but to arouse - to challenge others to form free opinions.

In my view, aiming at simplicity and lucidity is a moral duty of all intellectuals: lack of clarity is a sin, and pretentiousness is a crime.

We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant.

Bold ideas, unjustified anticipations, and speculative thought, are our only means for interpreting nature: our only organon, our only instrument, for grasping her. And we must hazard them to win our prize. Those among us who are unwilling to expose their ideas to the hazard of refutation do not take part in the scientific game.

It is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.

Philosophers should consider the fact that the greatest happiness principle can easily be made an excuse for a benevolent dictatorship. We should replace it by a more modest and more realistic principle - the principle that the fight against avoidable misery should be a recognized aim of public policy, while the increase of happiness should be left, in the main, to private initiative.

no matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans are white.

Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or 'given' base; and if we stop driving the piles deeper, it is not because we have reached firm ground. We simply stop when we are satisfied that the piles are firm enough to carry the structure, at least for the time being.

It is not possible to write clearly enough to avoid being misrepresented by people who are sufficiently determined to do so.

Science is not a system of certain, or -established, statements; nor is it a system which steadily advances towards a state of finality... And our guesses are guided by the unscientific, the metaphysical (though biologically explicable) faith in laws, in regularities which we can uncover-discover. Like Bacon, we might describe our own contemporary science-'the method of reasoning which men now ordinarily apply to nature'-as consisting of 'anticipations, rash and premature' and as 'prejudices'.

Philosophy is a necessary activity because we, all of us, take a great number of things for granted, and many of these assumptions are of a philosophical character; we act on them in private life, in politics, in our work, and in every other sphere of our lives -- but while some of these assumptions are no doubt true, it is likely, that more are false and some are harmful. So the critical examination of our presuppositions -- which is a philosophical activity -- is morally as well as intellectually important.

The difference between the amoeba and Einstein is that, although both make use of the method of trial and error elimination, the amoeba dislikes erring while Einstein is intrigued by it.

It is impossible to speak in such a way that you cannot be misunderstood.

If you know that things are bound to happen whatever you do, then you may feel free to give up the fight against them.

Whenever we propose a solution to a problem, we ought to try as hard as we can to overthrow our solution, rather than defend it.

A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others - not by simply taking over another's opinions, but by gladly allowing others to criticize his ideas and by gladly criticizing the ideas of others

We do not know. We can only guess.

Appealing to his [Einstein's] way of expressing himself in theological terms, I said: If God had wanted to put everything into the universe from the beginning, He would have created a universe without change, without organisms and evolution, and without man and man's experience of change. But he seems to have thought that a live universe with events unexpected even by Himself would be more interesting than a dead one.

The genuine rationalist does not think that he or anyone else is in possession of the truth; nor does he think that mere criticism as such helps us achieve new ideas. But he does think that, in the sphere of ideas, only critical discussion can help us sort the wheat from the chaff.