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 restricted 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.
</P>
<P>
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.
</P>
<P>
We extend these results outside the framework of pure 
propositional preferential entailments.