This paper presents a theory of instruction in the art of rhetorical invention and provides a basis for making decisions about teaching it. Invention is the process of inquiry through which one arrives at propositions and develops arguments in support of them. The author argues that by teaching invention along with the other arts of rhetoric, teachers are giving their students as complete an understanding as possible of what is involved in the process of writing. Four categories of invention are defined: systematic group, unsystematic group, systematic and unsystematic individual invention. Methods of instruction for each of the four categories are delineated. (TS)