 How then can one be certain that one is questioning the right thing? The Popperian answer is that we cannot have absolute certainty here, but repeated tests usually show where the trouble lies. As we saw, for Popper even observation statements are corrigible and open to review, and science in his view is not a quest for certain knowledge, but an evolutionary process in which hypotheses or conjectures are imaginatively proposed and tested in order to explain facts or to solve problems. For that reason, he emphasises both the importance of questioning the background knowledge when the need arises, and the significance of the fact that observation-statements are theory-laden and corrigible.