A Goal-Based Grammar Of Rhetoric

In many applications in computational linguistics, such as machine translation, we want to understand why a writer has used language in a particular way, what specific effects she intended to convey, and which linguistic choices were made to achieve those goals. This idea, that a writer has specific communicative goals or intentions in mind when she composes text, goes back to the study of classical rhetoric, in which the rhetorical form of a writer's text was considered to reflect his thoughts and intentions. The rhetorical form was realized through the appropriate choice and organization of words and syntactic structures meant to "evoke the desired response" (Corbett 1971). Content and form were recognized as inseparable, and as exerting a reciprocal influence upon each other. In our work, we have integrated the theory of classical rhetoric with conteml)orary work in knowledge rel)resentation to develop an approach to relating high-level intentions, through a hierarchy of increasingly detailed linguistic knowledge, to specific syntactic choices. We have constructed a multi-level grammar of rhetoric that ties rhetorical goals, such as formality and force, to syntactic choices, through the intermediary of stylistic goals such as clarity and concreteness. When a writer sets out to produce a piece of text, he does so with a specific pragmatic goal, such as informing or persuading, in mind. In order to achieve this goal, he must make particular linguistic choices. The mechanism that we propose for achieving the desired pragmatic effect is the use of lower-level rhetorical goals. For example, if the writer wishes to be I)ersuasive, he must. present the argument in such a way as to make the reader receptive to his message. Thus, he might use a combination of the rhetorical goals of force and amity to convey both a sense of authority and a desire to communicate. He must then decide on the specitic linguistic choices that will realize these rhetorical goals. Style is the medimrn that enables him to do this. In order to model formally the linguistic choices of a writer, we decompose complex rhetorical goals into simpler stylistic goals that can then be related to lexical, syntactic, and semantic choices.