The purpose of this study was to investigate whether and how students enact "responsibility" and "generativity" through their comments in asynchronous online discussions. "Responsibility" referred to discourse markers indicating participants' sense that their contributions are required in order to uphold their discursive obligations, and "generativity" referred to the capacity of comments to attract responses by virtue of content or stylistic features that convey voice or social presence. Participants were 24 graduate students and their instructor in a hybrid class, with face-to-face class meetings supplemented by three asynchronous online discussions around course readings. Discourse analytic techniques and naturalistic inquiry were used to analyze discussion transcripts. Results suggest that students differed in the degree to which they showed responsibility to the online discussions. They also differed in their generativity, as defined by the attractiveness, social responsiveness, and intellectual responsiveness their comments displayed. Interestingly, responsibility and generativity were not necessarily co-incident, with some students who had contributed many comments to the discussion having comments that were highly generative and others much less generative. Likewise, some students who were minimally responsible to their discursive obligations contributed comments that were nevertheless generative. We argue that responsibility and generativity contribute to a sense that computer-mediated discussion participants are members of a learning community, a sense that may be prerequisite for successful academic outcomes but may be difficult to create in online contexts where relationships may require more time and effort. Conclusions suggest how instructors and learners can help make online learning more productive.