The study of presumptions has intensified in argumentation theory over the last years. Although scholars put forward different accounts, they mostly agree that presumptions can be studied in deliberative and epistemic contexts, have distinct contextual functions, and promote different kinds of goals. Accordingly, there are “practical” and “cognitive” presumptions. In this paper, I show that the differences between practical and cognitive presumptions go far beyond contextual considerations. The central aim is to explore Nicholas Rescher’s contention that both types of presumptions (...) have a closely analogous pragmatic function, i.e., that practical and cognitive presumptions are made to avoid greater harm in circumstances of epistemic uncertainty. By comparing schemes of practical and cognitive reasoning, I show that Rescher’s contention requires qualifications. Moreover, not only do practical and cognitive presumptions have distinct pragmatic functions, but they also perform different dialogical functions and, in some circumstances, cannot be defeated by the same kinds of evidence. Hence, I conclude that the two classes of presumptions merit distinct treatment in argumentation theory. (shrink)

Traditionally, a presumption is a dialogically privileged, yet defeasible proposition that allocates the burden of proof to a party who challenges it. This paper investigates the strength of presumptions. First, it explains how ‘strength’ contributes to defining the concept of presumption. Second, it provides an overview of (contextual, justificatory, and deontic) factors determining a presumption’s strength. Finally, it analyses the predominant view that defines strength in terms of the Challenger’s burden of proof: the stronger (weaker) the presumptionp, the more (less) (...) difficult it is to prove non-p. I argue that the latter proposal applies only to practical presumptions, and that strength is conceived differently for cognitive presumptions. (shrink)