Hypothetical revision and matter-of-fact supp osition

The recent literature offers several models of the notion of matter-of-fact supposition 1 revealed in the acceptance of the so-called indicative conditionals. Some of those models are qualitative (Collins 1990), (Levi 1996), (Stalnaker 1984). Other probabilistic models appeal either to infinitesimal probability or two place probability functions ((van Fraassen 1995), (Joyce 1999), (McGee 1994)). Recent work has made possible to understand which is the exact qualitative counter-In this article we show that the qualitative notion of change that thus arises is hypothetical revision, a notion previously axiomatized in (Arló-Costa 1997) and (Arló-Costa & Thomason 1996). This notion is incompatible with AGM as well as with other standard methods of theory change (like Mendel-zon and Katsuno's UPDATE). The way in which matter-of-fact supposition is modeled via hypothetical revision is illustrated via examples. The model is compared with other qualitative models of indicative supposition (like the one offered in (Levi 1996) and (Stal-naker 1984)), with models of subjunctive supposition, as well as with some of the well know models of learning. Applications in the theory of games and decisions are considered.