Probabilistic Belief Change: Expansion, Conditioning and Constraining
  The AGM theory of belief revision has become an important paradigm for
investigating rational belief changes. Unfortunately, researchers working in
this paradigm have restricted much of their attention to rather simple
representations of belief states, namely logically closed sets of propositional
sentences. In our opinion, this has resulted in a too abstract categorisation
of belief change operations: expansion, revision, or contraction. Occasionally,
in the AGM paradigm, also probabilistic belief changes have been considered,
and it is widely accepted that the probabilistic version of expansion is
conditioning. However, we argue that it may be more correct to view
conditioning and expansion as two essentially different kinds of belief change,
and that what we call constraining is a better candidate for being considered
probabilistic expansion.
