  In this paper, we address the problem of change in an abstract argumentation
system. We focus on a particular change: the addition of a new argument which
interacts with previous arguments. We study the impact of such an addition on
the outcome of the argumentation system, more particularly on the set of its
extensions. Several properties for this change operation are defined by
comparing the new set of extensions to the initial one, these properties are
called structural when the comparisons are based on set-cardinality or
set-inclusion relations. Several other properties are proposed where
comparisons are based on the status of some particular arguments: the accepted
arguments; these properties refer to the evolution of this status during the
change, e.g., Monotony and Priority to Recency. All these properties may be
more or less desirable according to specific applications. They are studied
under two particular semantics: the grounded and preferred semantics.
