It is the rule which says that the other rules of scientific procedure must be designed in such a way that they do not protect any statement in science against falsification.
Karl PopperIt is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.
Karl PopperA 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.
Karl Popper