Able rhetoricians, including good writers and good lawyers, know how to make their points effectively, by arranging their arguments and choosing the appropriate language in which to convey them.
Classical rhetoricians divided the field into several varieties:
Deliberative rhetoric, the art of persuading an audience to take (or not to take) some action — think of senators addressing their peers, or lobbyists addressing their representatives;
Forensic rhetoric, the art of making a persuasive case in a legal matter, as when a lawyer argues for or against an accused person;
Epideictic rhetoric, the use of powerfully affective language to praise or blame someone or something — most odes are epideictic oratory, as are most inaugural addresses.
Those who study rhetoric have classified many hundreds of figures of speech, sometimes strictly ornamental, but often concerned with achieving certain effects. Many of them are used only by professional rhetoricians (erotesis, hypophora, epidiorthosis), and you needn't worry about them. But others are handy means of describing uses of literary language.
