Karl Popper

"Solitude is necessary for reflection and growth."

"The search for truth never ends."

"All human knowledge is provisional."

"Open discussion is the path to understanding."

"The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design."

"We are not makers of history. We are made by history."

"Science may be described as the art of systematic over-simplification."

"The more we learn about the world, and the deeper our learning, the more conscious, clear, and certain will the notion become that through our knowledge we can only change the world and achieve our ends by working within it."

"Every genuine test of a theory is an attempt to falsify it or to refute it."

"There is no way to avoid taking sides; but we can try to be aware of our bias and to correct for it."

"The attempt to make heaven on earth produces hell."

"Life is suffering. It is hard. The world is cursed. But all of this is as it should be - at least, it is all challenging."

"One can sum up any philosophy in fifteen minutes that it takes a man of talent to expound it in a book."

"Tolerance and friendship with those who hold different views are not signs of weakness but of strength."

"The growth of knowledge can be plotted as an asymptotic curve approaching, but never reaching, a limite of perfect knowledge."

"I think there is an important distinction between criticism and mere carping. Criticism is an attempt to help; carping is an attempt to hurt."

"We should look for a weak point in the argument, in the same way a doctor searches for the source of pain."

"Our knowledge is precious not because it is certain but because it is open to improvement."

"Always remember that it is impossible to speak in such a way that you cannot be misunderstood."

"The principle of tolerance must mean that I will not attempt, in matters of opinion, to prevent others from having a different opinion from mine."

"Common sense tells us that our existence is not the only fact we know. We know that there are laws of nature, roughly speaking, and that we are able to discover them."

"There has never been a better tool for teaching than the Socratic method, and Socrates never used notes."

"I am convinced that this is the task of every philosophy worthy of the name - to see that the intellectual and moral crisis of our time is a serious one."

"Everything is possible - the impossible just takes longer."

"Even the best of our theoretical science is largely a matter of faith."

"It is impossible to build paradise on earth; the attempt to do so leads to hell."

"A theory which is not refutable by any conceivable event is non-scientific."

"The demands of ethics are not 'categorical imperatives'; they are conditional demands of the form: if you wish to live in a certain kind of society, then you must learn a certain kind of behavior."

"We may become the makers of our fate when we cease to pose as its prophets."

"If we are uncritical we shall always find what we expect; we shall look for, and find, confirmations, and we shall ignore, or misjudge, the rest."