Underlying much twentieth century rhetorical theorizing has been the intuition that functionally and instrumentally, rhetoric requires a complement, for instance, dialectic or "dialogic." While the work of Maurice Natanson, Richard Weaver, and recent rhetoricians of inquiry provides a dialectical complement to instrumental rhetoric, another tradition in rhetoric represented by the work of Wayne Brockriede and Allen Clark explores dialogue as a complement to instrumental rhetoric. This essay postulates that the philosophy of dialogue developed by Martin Buber provides a coherent grounding for a dialogical/ontological rhetoric. It contrasts, respectively, instrumental and dialogical conceptions of the rhetorical situation and instrumental and dialogical characterizations of the rhetor, the rhetor's purposes and modes of influence. It concludes with a discussion of research issues confronting those interested in further development of a dialogic rhetoric.