  Argumentation is a non-monotonic process. This reflects the fact that
argumentation involves uncertain information, and so new information can cause
a change in the conclusions drawn. However, the base logic does not need to be
non-monotonic. Indeed, most proposals for structured argumentation use a
monotonic base logic (e.g. some form of modus ponens with a rule-based
language, or classical logic). Nonetheless, there are issues in capturing
defeasible reasoning in argumentation including choice of base logic and
modelling of defeasible knowledge. And there are insights and tools to be
harnessed for research in non-monontonic logics. We consider some of these
issues in this paper.
