The issue of knowing what it means for a group to have collective beliefs is being discussed more and more in contemporary philosophy of the social sciences and philosophy of mind. Margaret Gilbert’s reconsideration of Durkheim’s viewpoint in the framework of the plural subject’s account is one of the most famous. This has implications in the history and the sociology of science—as well asin the history and sociology of philosophy—although Gilbert only outlined them in the former fields and said nothing (...) about the latter. Symmetrically but independently, a historian of science, Mara Beller, has recently challenged Kuhn’s conception of the role of consensus in sciences in a brilliant analysis by carefully studying the history of Copenhagen School of Quantum Mechanics. Not only does she show the role of disagreement and controversies (doubting whether there was any collective belief characteristic in this group of physicists), but she even shakes up the very idea of individual beliefs. Each scientist (Heisenberg, Bohr, etc.) could be seen as divided into several selves. This paper contends that these two conceptions open important new horizons in several domains, especially if they are linked together. The paper assesses this claim in the light of empirical examples like the Vienna Circle, Copenhagen School, and, eventually, Cartesian philosophy. Key Words: plural subject • polyphony • collective briefs • Cartesian argumentation. (shrink)