 Clearly, most forms of defeasible reasoning are externally dynamic and hence most logics for defeasible reasoning violate Monotony: they have non-monotonic consequence relations for which consequences may not persist when new information is obtained. This feature is so central that the formal logical study of defeasible reasoning is often taken to be coextensive with the domain of NML where non-monotonicity is understood as a property of the consequence relation of a logic. 