Dictionary.net

The area of theory change in whichpreservation of the information in the theory to be changedplays a key role.A fundamental issue in belief revision is how to decide whatinformation to retract in order to maintain consistency, whenthe addition of a new belief to a theory would make itinconsistent. Usually, an ordering on the sentences of thetheory is used to determine priorities among sentences, sothat those with lower priority can be retracted. Thisordering can be difficult to generate and maintain.The postulates of the AGM Theory for Belief Revisiondescribe minimal properties a revision process should have.[Better definition?]