Karl Popper on falsifiability:
A property of any proposition for which it is possible to specify a set of circumstances the occurrence of which would demonstrate that the proposition is false. Falsifiability is the crucial feature of scientific hypotheses: beliefs that can never be tested against the empirical evidence are dogmatic.
Bertrand Russell’s teapot:
If I were to suggest that between the Earth and Mars there is a china teapot revolving about the sun in an elliptical orbit, nobody would be able to disprove my assertion provided I were careful to add that the teapot is too small to be revealed even by our most powerful telescopes. But if I were to go on to say that, since my assertion cannot be disproved, it is an intolerable presumption on the part of human reason to doubt it, I should rightly be thought to be talking nonsense. If, however, the existence of such a teapot were affirmed in ancient books, taught as the sacred truth every Sunday, and instilled into the minds of children at school, hesitation to believe in its existence would become a mark of eccentricity and entitle the doubter to the attentions of the psychiatrist in an enlightened age or of the Inquisitor in an earlier time.
If there is no way of proving something wrong, it’s not science. And if you can’t prove something wrong, that doesn’t make it right. Can you think of prime fat contemporary examples of both of these? I certainly can.