An intuitively appealing argument for pluralism in economics can be made on the grounds that schools of economic thought complement one another. Let us call this the complementarity-based argument for pluralism (CAP). The concepts of complementarity, pluralism, and school of thought are scrutinized in this paper to evaluate this argument. I argue that the complementarity of schools is relative to scientific goals, which implies that discussing complementarity of schools of economic thought requires discussing the goals of economic research. I also (...) distinguish weak from strong complementarity and show that some alleged complementarity relations between schools are weak and thus provide little support for CAP. However, if strong complementarity relations, relative to a valuable goal, can be demonstrated to exist between specific schools, this is a strong reason for pluralism about those schools. Finally, I provide suggestions on how to distinguish strong from weak complementarity. (shrink)