This paper studies the logical modelling of presumptions and their effects on the burden of proof. Presumptions are modelled as default rules and their effect on the burden of proof is defined in terms of a distinction between the burden of production, the burden of persuasion and the tactical burden of proof. These notions are logically characterised in such a way that presumptions enable a party to fulfil a burden of production or persuasion while shifting a tactical burden to the other party. Finally, it is shown how debates about what can be presumed can be modelled as debates about the backings of default rules.