Nietzsche on science and hypothesis:

"In science convictions have no rights of citizenship, as one says with good reason. Only when they decide to descend to the modesty of hypotheses, of a provisional experimental point of view, of a regulative fiction, they may be granted admission and even a certain value in the realm of knowledge—though always with the restriction that they remain under police supervision, under the police of mistrust." (The Gay Science, Aph. 344)