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.

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

It is wrong and dangerous to extol freedom by telling people that they will certainly be all right once they are free. The most we can say of democracy or freedom is that they give our personal abilities a little more influence on our well-being.

Do not allow your dreams of a beautiful world to lure you away from the claims of men who suffer here and now. Our fellow men have a claim to our help; no generation must be sacrificed for the sake of future generations.

There can be no ultimate statements science: there can be no statements in science which can not be tested, and therefore none which cannot in principle be refuted, by falsifying some of the conclusions which can be deduced from them.

A system is empirical or scientific only if it is capable of being tested by experience. These considerations suggest that not the verifiability but the falsifiability of a system is to be taken as a criterion of demarcation... It must be possible for an empirical or scientific system to be refuted by experience.

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.