Everything else being equal: A modal logic approach to ceteris paribus preferences Johan van Benthem, Olivier Roy, Patrick Girard Abstract: This paper presents a new modal logic for ceteris paribus prefer- ences understood in the sense of "all other things being equal". This reading goes back to the seminal work of Von Wright in the early 60's, and it returned in computer science in the 90's and in 'dependency logics' today. We show how it differs from ceteris paribus as "all other things being normal", which is used in contexts with preference defeaters. We provide a semantic analysis and several completeness theorems. We show how our system links up with Von Wright's work, but also with the mathematics of dynamic logic. Finally, we discuss applications to game-theoretic equilibria, and to agenda setting and preference change. Keywords: Ceteris Paribus Preferences; von Wright; Equality; Normality; Games