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. —But does this not mean, if you consider it more precisely, that a conviction may obtain admission to science only when it ceases to be a conviction? Would it not be the first step in the discipline of the scientific spirit that one would not permit oneself any more convictions? - Friedrich Nietzsche, The Gay Science, Book V, Aphorism 344.