In this third period (as it may be termed) of my mental progress, which now went hand in hand with hers, my opinions gained equally in breadth and depth, I understood more things, and those which I had understood before, I now understood more thoroughly. I had now completely turned back from what there had been of excess in my reaction against Benthamism. I had, at the height of that reaction, certainly become much more indulgent to the common opinions of society and the world, and more willing to be content with seconding the superficial improvement which had begun to take place in those common opinions, than became one whose convictions on so many points, differed fundamentally from them. I was much more inclined, than I can now approve, to put in abeyance the more decidedly heretical part of my opinions, which I now look upon as almost the only ones, the assertion of which tends in any way to regenerate society. x

He is a dreamer of ancient times, or rather, of the myths of what ancient times used to be. Such men are harmless in themselves, but their queer lack of realism makes them fools for others.

What is at stake here is precisely the problem of the fulfillment of desire: when we encounter in reality an object which has all the properties of the fantasized object of desire, we are nevertheless necessarily somewhat disappointed; we experience a certain this is not it; it becomes evident that the finally found real object is not the reference of desire even though it possesses all the required properties.

The analysis achieves its end when the patient is able to recognize, in the Real of his symptom, the only support of his being. That is how we must read Freud's 'wo we war, soll ich werden:' you, the subject, must identify yourself with the place where your symptom already was; in its pathological particularity you must recognize the element which gives consistency to your being.

The belief in a political Utopia is especially dangerous. This is possibly connected with the fact that the search for a better world, like the investigation of our environment, is (if I am correct) one of the oldest and most important of all the instincts.

I do not believe in what is often called... 'exact terminology'... [or] in definitions... [they] do not... add to exactness... I especially dislike pretentious terminology and... pseudo-exactness concerned with it.

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.

What can be said can and should always be said more and more simply and clearly.

There are uncertain truths - even true statements that we may take to be false - but there are no uncertain certainties. Since we can never know anything for sure, it is simply not worth searching for certainty; but it is well worth searching for truth; and we do this chiefly by searching for mistakes, so that we have to correct them.

I disbelieve in specialization and... experts. ...[P]aying too much respect to the specialist ...[is] destroying the commonwealth of learning, the rationalist tradition, and science ...

Why do I think that we, the intellectuals, are able to help? Simply because we, the intellectuals, have done the most terrible harm for thousands of years. Mass murder in the name of an idea, a doctrine, a theory, a religion - that is all our doing, our invention: the invention of the intellectuals. If only we would stop setting man against man - often with the best intentions - much would be gained. Nobody can say that it is impossible for us to stop doing this.

[T]here is only one way to science-or to philosophy... 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... more fascinating problem, or... obtain a solution. But even if you do... you may... discover, to your delight, the... a whole family of enchanting... perhaps difficult problem children for whose welfare you may work, with a purpose, to the end of your days.

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. Principle attributed to Popper by Ryszard Kapiscinski in New York Times obituary, 1995.

'[S]cientific knowledge' always remained sheer guesswork... controlled by criticism and experiment. ...[T]his assumption is sufficient for solving the problem of induction-called by Kant 'the problem of Hume'- without sacrificing empiricism...[i.e.,] without adopting a principle of induction and ascribing to it a priori validity. For guesses are not 'induced from observations' (although they may ...be suggested ...by observations). This ... allows us to accept ...(...without Russell's limits of empiricism) Hume's logical criticism of induction and to give up ...an inductive logic, for certainty, and even for probability, while continuing ...scientific search for truth.

Never aim at more precision than... required by the problem...

To be ignorant of the past is to remain a child.

All things living are in search of a better world.

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

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.

There are all kinds of sources of our knowledge; but none has authority ... The fundamental mistake made by the philosophical theory of the ultimate sources of our knowledge is that it does not distinguish clearly enough between questions of origin and questions of validity.

Scientists try to eliminate their false theories, they try to let them die in their stead. The believer-whether animal or man-perishes with his false beliefs.

There is no history of mankind, there is only an indefinite number of histories of all kinds of aspects of human life. And one of these is the history of political power. This is elevated into the history of the world. But this, I hold, is an offence against every decent conception of mankind. It is hardly better than to treat the history of embezzlement or of robbery or of poisoning as the history of mankind. For the history of power politics is nothing but the history of international crime and mass murder (including it is true, some of the attempts to suppress them). This history is taught in schools, and some of the greatest criminals are extolled as heroes. Vol 2, Ch. 25 "Has History any Meaning?" Variant: There is no history of mankind, there are only many histories of all kinds of aspects of human life. And one of these is the history of political power. This is elevated into the history of the world.

Diversity makes critical argument fruitful. ...[P]artners in an argument must share ...the wish to know, and the readiness to learn from the other ...by severely criticizing his views... and hearing... [the] reply. ...the so-called method of science consists in this kind of criticism.

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.

It seems to me certain that more people are killed out of righteous stupidity than out of wickedness.

In speaking of sociological laws or natural laws of social life I have in mind such laws as are formulated by modern economic theories, for instance, the theory of international trade, or the theory of the trade cycle. These and other important sociological laws are connected with the functioning of social institutions. These laws play a role in our social life corresponding to the role played in mechanical engineering by, say, the principle of the lever. For institutions, like levers, are needed if we want to achieve anything which goes beyond the power of our muscles. Like machines, institutions multiply our power for good or evil. Like machines, they need intelligent supervision by someone who understands their way of functioning and, most of all, their purpose, since we cannot build them so that they work entirely automatically.

[E]ven serious students are misled by the myth of the subject.

Science may be described as the art of systematic over-simplification - the art of discerning what we may with advantage omit.

It is wrong to think that belief in freedom always leads to victory; we must always be prepared for it to lead to defeat. If we choose freedom, then we must be prepared to perish along with it. Poland fought for freedom as no other country did. The Czech nation was prepared to fight for its freedom in 1938; it was not lack of courage that sealed its fate. The Hungarian Revolution of 1956 - the work of young people with nothing to lose but their chains - triumphed and then ended in failure. ... Democracy and freedom do not guarantee the millennium. No, 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.

I believe that the advance of science depends upon the free competition of thought, and thus upon freedom, and that it must come to an end if freedom is destroyed (though it may well continue for some time in some fields, especially in technology).

Always remember that it is impossible to speak in such a way that you cannot be misunderstood: there will always be some who misunderstand you.

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.

A rationalist, as I use the word, is a man who attempts to reach decisions by argument and perhaps, in certain cases, by compromise, rather than by violence. He is a man who would rather be unsuccessful in convincing another man by argument than successful in crushing him by force, by intimidation and threats, or even by persuasive propaganda.

Scientific theories are distinguished from myths... in being criticizable, and... open to modifications... They can be neither verified nor probabilified.

Good tests kill flawed theories; we remain alive to guess again.

If I were to give a simple formula or recipe for distinguishing between what I consider to be admissible plans for social reform and inadmissible Utopian blueprints, I might say: Work for the elimination of concrete evils rather than for the realization of abstract goods. Do not aim at establishing happiness by political means. Rather aim at the elimination of concrete miseries.

We must plan for freedom, and not only for security, if for no other reason than that only freedom can make security secure.

Scientific Method... [is] even less existent than some other non-existent subjects.

It seems to me that I may be living too long. Indeed: my nearest relations have all died, and so have some of my best friends, and even some of my best pupils. However, I do not have a reason to complain. I am grateful and happy to be alive, and still be able to continue with my work, if only just. My work seems to me more important than ever.

The more we learn about the world, and the deeper our learning, the more conscious, specific, and articulate will be our knowledge of what we do not know, our knowledge of our ignorance. For this, indeed, is the main source of our ignorance - the fact that our knowledge can be only finite, while our ignorance must necessarily be infinite. Variant translation: The more we learn about the world, and the deeper our learning, the more conscious, clear, and well-defined will be our knowledge of what we do not know, our knowledge of our ignorance. The main source of our ignorance lies in the fact that our knowledge can only be finite, while our ignorance must necessarily be infinite.

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.

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.

For it was my master who taught me not only how very little I knew but also that any wisdom to which I might ever aspire could consist only in realizing more fully the infinity of my ignorance.

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.

The history of mankind could... be described as a history of outbreaks of fashionable philosophical and religious maladies. These... have... one serious function... evoking criticism.

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

Do not allow your dreams of a beautiful world to lure you away from the claims of men who suffer here and now.

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

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.

I think so badly of philosophy that I don't like to talk about it. ... I do not want to say anything bad about my dear colleagues, but the profession of teacher of philosophy is a ridiculous one. We don't need a thousand of trained, and badly trained, philosophers - it is very silly. Actually most of them have nothing to say.