 This weakness of the probability axioms generates the famous problem of the priors, the problem of saying where initial probabilities come from. Are they always based on evidence previously collected? If so, how does scientific inquiry get started? If instead they’re not based on previous evidence but are a priori, what principles govern this a priori reasoning? Formal epistemologists are split on this question. The so-called objectivists see the probability axioms as incomplete, waiting to be supplemented by additional postulates that determine the probabilities with which inquiry should begin. (The Principle of Indifference (PoI) is the leading candidate here. See the entry on the  interpretation of probability.)  The so-called subjectivists think instead that there is no single, correct probability function \(p\) with which inquiry should begin. Different inquirers may begin with different values for \(p\), and none of them is thereby more or less scientific or rational than the others.