The title promises a chapter about methods, so a confession is in order. Here, as everywhere, my concerns are substantive, not methodological. Still, what one wants to learn and how one ought to go about learning it are intertwined. So, I propose to bring out the logic of the survey experiment by presenting a classification of survey experiment designs. Specifically, I distinguish three designs: manipulative, permissive, and facilitative. The distinctions among the designs turn on the hypotheses being tested, not the operations performed, and, above all, on the role of predispositions. The first design aims to get people to do what they are not predisposed to do; the second to allow them to do what they are predisposed to do, without encouraging them; and the third to provide them with a relevant reason to do what they already are predisposed to do. Against the background of this threefold classification, I want to comment briefly on some issues of causal inference and external validity and then conclude by offering my own view on the reasons for the explosive growth in survey experiments in the study of public opinion.

The modern survey experiment is the biggest change in survey research in a half century. There is some interest in how it came about, I am told. So I begin by telling how I got the idea of computer-assisted survey experiments.