Moinard, Yves and Rolland, Raymond Circumscriptions from what they cannot do (Preliminary report) , Common Sense'98 , Qween Mary and Westfield College, University of London , London , 20--41 , jan , 1998 , Document Abstract We show that, in the finite propositional case, traditional circumscriptions can be fully described only from the formulas which can never come as a result of the given circumscription (the ``inaccessible formulas''). Some work has already been done on the subject. Siegel and Forget have introduced the general notion of X-logic, and they have considered the case of finite propositional circumscriptions. However, their result is r estricted to the case where no varying proposition appears, which is known to be a severe restriction in terms of expressivity. We extend this result in the finite propositional case to any cumulative preferential entailment, thus in particular to any ``traditional circumscription'', that is we allow varying propositions. Moreover, we describe the smallest possible set which can be used for this purpose. We exhibit a spectacular duality between the traditional approach of a given cumulative preferential entailment, and the approach through the inaccessible formulas of this preferential entailment, i.e. the X-logic approach. We extend these results outside the framework of pure propositional preferential entailments. This web site is maintained by René Quiniou using the Weave system from the Caravel project: http://www-caravel.inria.fr. Last modification: 10-07-2011 09:54:25