Flipped classroom approaches remove the traditional transmissive lecture and replace it with active in-class tasks and pre-/post-class work. Despite the popularity of these approaches in the media, Google search, and casual hallway chats, there is very little evidence of effectiveness or consistency in understanding what a flipped classroom actually is. Although the flipped terminology is new, some of the approaches being labelled "flipped" are actually much older. In this paper, we provide a catch-all definition for the flipped classroom, and attempt to retrofit it with a pedagogical rationale, which we articulate through six testable propositions. These propositions provide a potential agenda for research about flipped approaches and form the structure of our investigation. We construct a theoretical argument that flipped approaches might improve student motivation and help manage cognitive load. We conclude with a call for more specific types of research into the effectiveness of the flipped classroom approach.