The Dempster-Shafer (DS) theory of probabilistic reasoning is presented in terms of a semantics whereby every meaningful formal assertion is associated with a triple (p, q, r) where p is the probability "for" the assertion, q is the probability "against" the assertion, and r is the probability of "don't know". Arguments are presented for the necessity of "don't know". Elements of the calculus are sketched, including the extension of a DS model from a margin to a full state space, and DS combination of independent DS uncertainty assessments on the full space. The methodology is
Arthur P. Dempster