Rhetoric George Campbell defines rhetoric as "the art or talent by which discourse is adapted to its end. The four ends of discourse are to enlighten the understanding, please the imagination, move the passion, and influence the will." The success of each of these four components of rhetoric can render an argument either effective or ineffective. Campbell therefore defines effective rhetoric mainly in terms of its aims, rather than in terms of the components of the discourse itself such as ethos, pathos, and logos.

Any effective rhetoric will "enlighten the understanding." One of the foremost jobs of a rhetorician is to deepen the audience's understanding on his or her chosen subject. For example, if a speaker is discussing global warming, he or she will want to provide some background information on the phenomenon: perhaps the history of global warming and the basic scientific...

Enlightening the understanding entails the development of knowledge through learning. The rhetorician acts as a sort of teacher for this aim of rhetoric. Whether a writer or a public speaker, a rhetorician needs to enlighten the understanding of the audience. Without enlightening the audience and increasing understanding of the subject matter, the audience may leave confused or disillusioned, and the speaker (or writer) will lose his or her credibility as an effective rhetorician. Furthermore, without enlightening the understanding, the rhetorician may lose the audience's attention altogether, thereby defeating the original purpose of the argument. The function of enlightening the understanding is primarily to provide an intellectual and factual foundation for the argument.
To "please the imagination" is one of the most difficult tasks of the rhetorician. Pleasing the imagination may involve invoking mental imagery in the audience. For example, a writer may describe in detail the suffering of children in Africa to stimulate the audience to donate money to a charity. By offering poignant examples that pertain to the subject matter, the…