In this paper, a logic for reasoning about coalitional power is developed which explicitly represents agents' preferences and the actions by which the agents can achieve certain results. A complete axiomatization is given and its satisfiability problem is shown to be decidable and EXPTIME-hard. Keywords Modal logic · Multi-agent systems · Collective agency Introduction Cooperation of agents plays a major role in many fields such as computer science, economics, politics, social sciences and

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... sophy. Agents can decide to cooperate and to form groups in order to share complementary resources or because as a group they can achieve something better than individually. When analyzing interactive situations involving multiple agents, we are interested in what results agents can achieve-individually or together as groups. There can be many ways how agents can achieve some result. They can differ significantly, e.g. with respect to their feasibility, costs or side-effects. Hence, it is not only relevant what results groups of agents can achieve but also how exactly they can do so. In other words, plans and actions also play a central role if we want to reason about cooperation in an explicit way. However, cooperative ability of agents expressed only in terms of results and actions that lead to these results does not tell us why a group of agents would actually decide to achieve a certain result. We also need to take into account the preferences based on which the agents decide what to do. Summarizing, we can say that in interactive situations, the following three questions are of interest: