A modal logic interpretation of Dempster's rule of conditioning is develope
d. It is shown that by restricting a model of modal logic in a non-trivial
way, the measures induced by this restricted model are, in fact, the condit
ional measures given the restricting set, corresponding to the measures ind
uced by the original model. (C) 1999 Elsevier Science B.V. All rights reser
ved.