 They presuppose that the premises’ exact probabilities are known. In practical applications, however, there might only be partial information about the probability of a premise \(\gamma\): its exact value is not known, but it is known to have a lower bound \(a\) and an upper bound \(b\) (Walley 1991). In such applications it would be useful to have a method to calculate (optimal) lower and upper bounds for the probability of the conclusion in terms of the upper and lower bounds of the probabilities of the premises.