 Some worry that, except for obeying the axioms of probability, degrees of belief are in the end assigned in a subjective and arbitrary manner (Allen and Pardo 2019). This worry can be alleviated by noting that degrees of belief should reflect a conscientious assessment of the evidence available which may also include empirical frequencies (see  §1.2  below and the examples in ENFSI 2015). In some cases, however, the relevant empirical frequencies will not be available. When this happens, degrees of belief can still be assessed by relying on common sense and experience. Sometimes there will be no need to assign exact probabilities to every statement about the past. In such cases, the relevant probabilities can be expressed approximately with sets of probability measures (Shafer 1976; Walley 1991), probability distributions over parameter values, or intervals (see later in  §1.4).