This paper joins the voices warning against hasty transference of legal concepts of presumption to other kinds of argumentation, especially to deliberation about future acts and policies. Comparison of the pragmatics which respectively constitute the illocutionary acts of accusing and proposing reveals important differences in the ways presumptions prompt accusers and proposers to undertake probative responsibilities and, also, points to corresponding differences in their probative duties. This comparison has theoretically important implication regarding the norms governing persuasive argumentation. The paper is (...) based on a broadly Gricean account of speech acts. (shrink)