PRELIMINARY DEFINITIONS AND DISTINCTIONS
What is an unintended consequence? An unintended consequence is an unenvisioned eﬀect of a purposive act, law, or policy to which human beings and other organisms adapt their behavior. Although we certainly adapt to natural events-for example, after a hurricane we may decide to move out of a storm surge area-, social theorists reserve the category of “unintended consequences” for adaptive responses to purposive human action. This restricted usage makes sense, given that we typically are most interested in those consequences over which we have some degree of control. I will argue over the course of this book that unanticipated and unhappy adaptive responses to policies, rules and choices can indeed sometimes be foreseen and avoided.