The causal relationships among the three presences in the Community of Inquiry (CoI) framework are explored and tested in this paper. The CoI framework has been used extensively in the research and practice of online and blended learning contexts. With the development of a survey instrument based on the CoI framework, it is possible to test the hypothesized causal relationships that teaching and social presence have a significant perceived influence on cognitive presence and that teaching presence is perceived to influence social presence. The results of this study confirm the factor structure of the CoI survey and the hypothesized causal relationships among the presences predicted by the CoI framework. These results point to the key role of teaching presence in establishing and sustaining a community of inquiry. Further research is called for to explore the dynamic relationships among the presences across disciplines and institutions as well as understand the existence and role of the specific sub-elements (categories) of each presence. (Contains 1 figure and 1 table.)