Popper on Scientific Progress

‎"The method of trial and error is a method of eliminating false theories by observation statements; and the justification for this is the purely logical relationship of deducibility which allows us to assert the falsity of universal statements if we accept the truth of singular ones. Another question sometimes asked is this: why is it reasonable to prefer non-falsified statements to falsified ones?...

We search for truth (even though we can never be sure we have found it), and because the falsified theories are known or believed to be false, while the non-falsified theories may still be true. Besides, We do not prefer every non-falsified theory – only one which, in the light of criticism, appears to be better than its competitors: which solves our problems, which is well tested, and of which we think, or rather conjecture or hope (considering other provisionally accepted theories), that it will stand up to further tests"

--- Conjectures and Refutations / Karl Popper