The diversity of mental health care “schools” or therapeutic perspectives poses problems in selecting and using any single therapeutic perspective. This article describes the genesis of clinical controversy—that is, how two or more therapeutic perspectives of the same clinical situation can be so different yet not necessarily differ in outcome. Ideas drawn from contemporary philosophy of science show how different “schools” derive separate, incompatible sets of scientific evidence from the same clinical situation. The school or theory determines (in part) not just what evidence is used, but what evidence is actually perceived. The authors conclude by recommending a pluralistic approach to mental health care; they map out some consequences of this pluralism and suggest some strategies for minimizing the disadvantages of “mixing and matching” therapeutic