On the Responsibility for Undecisiveness in Preferred and Stable Labellings in
Abstract Argumentation (Extended Abstract)?
Abstract
Different semantics of abstract Argumentation
Frameworks (AFs) provide different levels of decisiveness for reasoning about the acceptability of
conflicting arguments. The stable semantics is useful for applications requiring a high level of decisiveness, as it assigns to each argument the label “accepted” or the label “rejected”. Unfortunately, stable labellings are not guaranteed to exist, thus raising the question as to which parts of
AFs are responsible for the non-existence. In this
paper, we address this question by investigating
a more general question concerning preferred labellings (which may be less decisive than stable labellings but are always guaranteed to exist), namely
why a given preferred labelling may not be stable
and thus undecided on some arguments. In particular, (1) we give various characterisations of parts of
an AF, based on the given preferred labelling, and
(2) we show that these parts are indeed responsible
for the undecisiveness if the preferred labelling is
not stable. We then use these characterisations to
explain the non-existence of stable labellings