Karl Popper

"To be free is to be responsible for our choices."

"The most important tool in science is the question, not the answer."

"We cannot change what we refuse to understand."

"The strength of an argument lies not in its certainty, but in its ability to withstand criticism."

"History is the record of human attempts to solve problems, both successfully and unsuccessfully."

"To learn is to embrace uncertainty and to move forward despite it."

"The pursuit of truth requires the courage to admit when we are wrong."

"Our institutions are only as good as our willingness to reform them."

"The greatest discovery is not a new fact, but a new way of seeing."

"We must teach people to think, not what to think."

"The open mind is not empty; it is full of questions."

"The growth of knowledge is the only field in which we can say that humanity is making real progress."

"We are not students of some subject matter, but students of problems. And problems may cut right across the borders of any subject matter or discipline."

"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."

"Science must begin with myths, and with the criticism of myths."

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

"All life is problem-solving."

"If we are to solve our problems, we must learn to live with them and not run away."

"The open society is one in which men are urged, by and large, to give reasons for their convictions."

"Good friends, for the sake of experiment, we should accept one another's point of view."

"We are not interested in the agreement between the theory and the facts. Disagreement is what we want."

"The paradox is only a conflict between reality and your feeling of what reality ought to be."

"I am against obscurantism. I am for clarity in all things."

"The closed society is afraid of change."

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

"We must plan for freedom, and this means we must plan to keep the use of force in the hands of the public authorities."

"The tragedy of the great visionary is that he fails to see that his visions need not imply complete renovation."

"A theory is tested by attempting to refute it, not by confirming it."

"Our responsibility is to seek out the truth, even if we never quite find it."

"There is nothing in the natural world that corresponds to the ideal of the perfectly closed system."