This paper traces the evolution of the concept of presumption from a subordinate part of the Roman law to a central feature of legal disputations in medieval law. Special attention will be given to the second edition of the Libellus Pylei Disputato rius by Pilius of Medicina, and to the anonymous Tractatus de Praesumptionibus. My analysis will emphasize elements of these developments useful in the renewed discussion about the role of presumptions in argumentation stimulate d particularly by Richard Gaskins' Burdens (...) of Proof in Modern Discourse, highlighting the paradigmatic significance of rhetorical manipulations of burdens of proof in legal reasoning. (shrink)