The only way to test a hypothesis is to look for all the information that disagrees with it.
The growth of knowledge depends entirely upon disagreement.
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.
True ignorance is not the absence of knowledge, but the refusal to acquire it.
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.
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.
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.
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.
If we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.
No rational argument will have a rational effect on a man who does not want to adopt a rational attitude.
Those who promise us paradise on earth never produced anything but a hell.
You cannot have a rational discussion with a man who prefers shooting you to being convinced by you.
Every solution of a problem raises new unsolved problems.
It is not possible to write clearly enough to avoid being misrepresented by people who are sufficiently determined to do so.
It can’t happen here is always wrong: a dictatorship can happen anywhere.
We do not know. We can only guess.
It is part of my thesis that all our knowledge grows only through the correcting of our mistakes.