While the independent contributions of synchronous and asynchronous interaction in online learning are clear, comparatively less is known about the pedagogical consequences of using both modes in the same environment. In this study, we examine relationships between students' use of asynchronous discussion forums and synchronous private messages (PM). We find that asynchronous notes contain more academic language and less social language, are more difficult to read, and are longer compared to PM. In addition, we find that the most active forum-posters are also the most active PM users, suggesting that PMing is not reducing their contribution to public discourse. Finally, we find that those who frequently PM are less likely to rapidly scan forum notes, and that they spend more time online than those who make less use of PM. We suggest that PM supports asynchronous discussions in the formation of a community of inquiry.