In this paper, I develop a speech-act based account of presumptions. Using a score-keeping model of illocutionary games, I argue that presumptions construed as speech acts can be grouped into three illocutionary act types defined by reference to how they affect the state of a conversation. The paper is organized into two parts. In the first one, I present the score-keeping model of speech act dynamics; in particular, I distinguish between two types of mechanisms—the direct mechanism of illocution and the (...) indirect one of accommodation—that underlie the functioning of illocutionary acts. In the second part, I use the presented model to distinguish between the unilateral act of individual presumption, the point of which is to shift the burden of proof by making the hearer committed to justifying his refusal to endorse the proposition communicated by the speaker, whenever he refuses to endorse it, the bilateral act of joint presumption—‘bilateral’ in that it is performed jointly by at least two conversing agents—the function of which is to confer on the proposition endorsed by the speaker the normative status of jointly recognized though tentative acceptability, and the indirect or back-door act of collective presumption, the purpose of which is to sustain rules and practices to which the conversing agents defer the felicity of their conversational moves. (shrink)