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.

Definitions.... are never really needed, and rarely of any use

We hate the very idea that our own ideas may be mistaken, so we cling dogmatically to our conjectures.

It is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.

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.

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

The war of ideas is a Greek invention. It is one of the most important inventions ever made. Indeed, the possibility of fighting with with words and ideas instead of fighting with swords is the very basis of our civilization, and especially of all its legal and parliamentary institutions.