Axiomatic characterizations of two semi-revision operators are reported. To make this process comply with the Principle of minimal Change, a special evidence metric is introduced for measuring distance between states of knowledge. Then a novel semantics of knowledge bases is developed suggesed by the heuristics of weighted maximally consistent subsets . The latter is efficiently applied to the processes of consistent and inconsistent acquisition of knowledge, belief revision and contraction. Recovery can be satisfied even when there is more mutilation than is necessary.
Recovery also ensures that very often too little is given up in a contraction.
I show that some of the most serious inadequacies of the AGM -theory derive from early claims in some of its founding contributions, claims that have not been seriously questioned within the tradition since. The upshot of these investigations is that recovery cannot, and should not, be recovered. Theory contraction is hysteretic. Whether the AGM -theory can now recover is a good question.