The scientific method refers to ways to get facts, correct errors and mistakes, and test theories. The Oxford English Dictionary says that scientific method is: "a method or procedure that has characterized natural science since the 17th century". It is observation, measurement, and experiment, plus the formulation, testing, and modification of hypotheses. A scientist gathers empirical and measurable evidence, and uses sound reasoning. New knowledge often needs adjusting, or fitting into, previous knowledge. Criterion What distinguishes a scientific method of inquiry is a question known as the criterion'. It is an answer to the question: is there a way to tell whether a concept or theory is science, as opposed to some other kind of knowledge or belief? There have been many ideas as to how it should be expressed. Logical positivists thought a theory was scientific if it could be verified (proved true). Karl Popper thought this was a mistake. He thought a theory was not scientific unless there was some way it might be refuted (shown to be wrong). On the other hand, Paul Feyerabend thought...