Logic and Logical Philosophy Volume 17 (2008), 185–207 Caroline Semmling and Heinrich Wansing FROM BDI AND stit TO bdi -stit LOGIC ∗ Abstract. Since it is desirable to be able to talk about rational agents form- ing attitudes toward their concrete agency, we suggest an introduction of doxastic, volitional, and intentional modalities into the multi-agent logic of deliberatively seeing to it that, dstit logic. These modalities are borrowed from the well-known BDI (belief-desire-intention) logic. We change the se- mantics of the belief and desire operators from a relational one to a monotonic neighbourhood semantic in order to handle ascriptions of conflicting but not inconsistent beliefs and desires as being satisfiable. The proposed bdi-stit logic is defined with respect to branching time frames, and it is shown that this logic is a generalization of a bdi logic based on branching time possible worlds frames (but without temporal operators) and dstit logic. The new bdi -stit logic generalizes bdi and dstit logic in the sense that for any model of bdi or dstit logic, there is an equivalent bdi -stit model. Keywords: modal logic of agency, deliberative stit logic, BDI logic, beliefs, desires, intensions, neighbourhood semantics, branching time structures. 1. Introduction The temporal logics BDI and BDI ∗ of beliefs, desires, and intentions, de- veloped by Rao and Georgeff [9] are among the most prominent and widely applied formalizations of rational agents, see also [20]. In this paper, we shall introduce a modal logic of beliefs, desires, intentions, and agency. Sup- plementing the BDI vocabulary by a modal operator for agency is a very ∗ We dedicate this paper to the memory of Alexander Vladimirovich Kuznetsov (1926– 1984). Special Issue To the memory of A.V. Kuznetsov. Guest Editors: A. Muravitsky and S. Odintsov