In a world in which online interactions are becoming the norm, an understanding of how three fundamental aspects of online learning (teaching presence, social presence and cognitive presence) interact is important. This paper will look at how these three presences interact with each other in an online forum. More specifically it will describe the effects of instructional design on learners' levels of critical thinking and social presence. The research involved taking 900 learner posts from differing experimental conditions and analyzing those posts for social presence and critical thinking. The experimental conditions varied in three different ways in regards to the level of instructor control over the learning environment. The first learning environment had a low level of instructor control while the second and third had progressively high levels of instructor control over the learners' contributions to the forum. The results showed that increasing the amount of control an instructor has over a learning environment increases the amount of cognitive presence but decreases the amount of social presence within the learners' posts. In general, these results are important because instructors must be aware of how their behavior may affect how learners interact (and therefore learn) online. More specifically, many instructors are interested in the types of discourse their learners create. Therefore, the ways instructors can manipulate learner discourse is of great importance.