Learning is a social process (Harasim, 2002; Swan & Shea, 2005; Tu, 2000). Discourse plays a key role in the social process of learning (Harasim, 2002). Therefore, it is extremely important that we understand how students and teachers socially interact in online courses where asynchronous computer mediated communication (CMC) is the major form of discourse. Theories of social presence help explain how students and teachers interact and learn online.
Patrick R. Lowenthal. "Social Presence" Encyclopedia of distance and online learning (2nd ed). Ed. P. Rogers, G. Berg, J. Boettcher, C. Howard, L. Justice, & K. Schenk. Hershey, PA: IGI Global, 2009. 1900-1906.