When is argumentation deductive?

This paper discusses and compares various answers to the question when argumentation is deductive. This includes an answer to the questions when argumentation is defeasible and whether defeasible argumentation is a subclass of deductive argumentation or whether it is a distinct form of argumentation. It is concluded that deductive and defeasible argumentation as conceived by Philosophers like Pollock and Rescher and as formalised in the ASPIC framework and systems like Defeasible Logic Programming, are semantically different categories. For this reason, purely syntactic base logic approaches to formal argumentation are unsuitable for characterising this distinction.