Karl R. Popper

The so-called paradox of freedom is the argument that freedom in the sense of absence of any constraining control must lead to very great restraint, since it makes the bully free to enslave the meek. The idea is, in a slightly different form, and with very different tendency, clearly expressed in Plato.

Science may be described as the art of systematic oversimplification.

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

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.

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

No book can ever be finished. While working on it we learn just enough to find it immature the moment we turn away from it.

All life is problem solving.

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

Our knowledge can only be finite, while our ignorance must necessarily be infinite.