"Purpose" is an important term in rhetorical theory and writing pedagogy. An analysis of the presentation of "purpose" in three well-regarded, theory-based textbooks ("Writing in the Liberal Arts Tradition: A Rhetoric with Readings,""Writing with a Purpose," and "Form and Surprise in Composition") suggests that "purpose" is a more complex and relative concept than is typically acknowledged. All three textbooks present radically different versions of "purpose," corresponding to three different rhetorical traditions: Classical-Poetic, Romantic, and Classical-Rhetorical. It makes more sense to think of "purpose" in writing as a relative term with meanings that vary in particular kinds of rhetorical situations. For example, in highly determined social contexts, "purpose" is the action that writers want their readers to take with respect to an exigence. On the other extreme are "free" rhetorical situations in which the audience is not specified, the exigence not given, the genre unknown--the type of writing sometimes assigned in freshman writing. Because the meaning of "purpose" is unstable, teachers should not generalize about how writers arrive at "purpose." In addition, "purpose" should always be seen as relative to the particular social situation that the writing course imagines itself serving. (MM)