Our arguments are intended not only for those who are innocent of the technicalities of causal inference but also aim to offer something to those who are well versed with the field. Most of what is in the paper is known to someone in some subject. But what epidemiology knows is not what is known by economics, or political science, or sociology, or philosophy—and the reverse. The literatures on RCTs in these areas are overlapping but often quite different; each uses its own language and different understandings and misunderstandings characterize different fields and different kinds of projects. We highlight issues arising across a range of disciplines where we have observed misunderstanding among serious researchers and research users, even if not shared by all experts in those fields. Although we aim for a broad cross-disciplinary perspective, we will, given our own disciplinary backgrounds, be most at home with how these issues arise in economics and how they have been treated by philosophers. good contents