Gilbert (2000) examined the issue of collective intentionality in science. Her paper consisted of a conceptual analysis of the negative role of collective belief, consensus, and joint commitment in science, with a brief discussion of a case study investigated by Thagard (1998a, 1998b). I argue that Gilbert's concepts have to be refined to be empirically more relevant. Specifically, I distinguish between different kinds of joint commitments. I base my analysis on a close examination of Thagard's example, the discovery of Helicobacter (...) pylori, and two other historical cases involving the Copenhagen school of quantum mechanics and the Austrian school of economics. I also argue that it is difficult to fulfill the condition of common knowledge, even in Gilbert's weak sense. I conclude by raising serious doubts about the very possibility of a certain type of joint commitment, which I refer to as an implicit joint commitment. (shrink)