2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/90850The decoherent (consistent) histories formalism has been proposed as a means of eliminating measurements as a fundamental concept in quantum mechanics. In this formalism, probabilities can be assigned to any description which satisfies a particular consistency condition. The formalism, however, admits incompatible descriptions which cannot be combined, unlike classical physics. This seems to leave an ambiguity in the choice of the description. I argue that this ambiguity is removed by considering the observer as a physical system.17 pages, SPROCL LaTeX macros. To appear in proceedings of ``Foundations of Probability in Physics 2, Vaxjo, Sweden, June 2002.''Quantum Physicstext