ABSTRACT In the relatively nascent field of placebo studies, empirical studies have burgeoned. Yet debate about how to define the terms placebo and “placebo ef- fect” has not abated. A number of prominent scholars (drawn from medical practice, as well as philosophy, psychology, and anthropology) continue to propose and defend different conceptual models for these terms, and the perception that conceptual de- bate persists is often given as one justification for new definitions. Paradoxically—in spite of this lively debate—this article finds considerable underlying agreement about definitional matters within placebo studies. Drawing on key insights from philosophy of science, and by exploring the nature of scientific consensus and normal scientific research, this paper argues that well-developed placebo concepts form the basis for a placebo paradigm and that conceptual disagreement is overstated. A COMMON OBSERVATION IN PLACEBO studies is that definitional disagreement is rife. Philosopher and historian of science Robin Nunn (2009a) recently Program in Placebo Studies, General Medicine, and Primary Care Research, Beth Israel Deaconess Medical Center, Harvard Medical School; and School of Psychology, University College Dublin. Correspondence: General Medicine and Primary Care Research, 330 Brookline Avenue, Boston MA 02215. Email: cblease@bidmc.harvard.edu. This research was funded by an Irish Research Council-Marie Sklodowska-Curie Award (CLNE/2017/226) and a Fulbright Scholar Award. The author thanks Franklin Miller for feedback on an earlier draft of this paper. Perspectives in Biology and Medicine, volume 61, number 3 (summer 2018): 412–429. © 2018 by Johns Hopkins University Press 412 Consensus in Placebo Studies lessons from the philosophy of science Charlotte Blease