“Rhetoric” has usually been defined as the study of methods of using language to persuade other people. In other words, “rhetoric” tends to be argumentative writing or speech, intended to change people’s minds. Often, however, “rhetoric” is considered the study of any use of language meant to be persuasive or appealing. “Rhetoric” can also be defined more narrowly as the study of the various devices or “turns” of language (“tropes”) or “figures of speech” that can make language memorable and effective. Such figures of speech include, for example, metaphors, similes, paradoxes, puns, assonance, alliteration, and hundreds of others. Guides to rhetoric often list, explain, and illustrate such figures of speech.
“Prosody” refers to the study of meter, or regular patterns of rhythm, especially in poetry. For example, English poetry often uses “iambic pentameter” meter: ten syllables in which the even syllable is stressed and the odd syllable is unstressed, as in the following famous line written by Christopher Marlowe: “Was this the face that launched a thousand ships?” Once a metrical pattern has been established, a talented poet can work all kinds of interesting and meaningful variations on it. “Prosody” is the study of the ways writers use rhythms and meters.
I was going to give this the same once-over I've been giving everyone else, but this is something I actually care about and I want you to understand it. So listen up, kiddo.
Rhetoric is how you use language to persuade someone or argue for something. Classical Rhetoric is composed of Ethos (the legitimacy of what you're saying), Pathos (the emotional appeal of what you're saying), and Logos (the logic of what you're saying). The way I remember it is Ethos=Ethics, Pathos=Pathetic (but not pathetic, ya know...?), and Logos=Logic. Anyway, these three things are the foundation of a good argument, according to the ancient Greeks. However, "rhetoric," today, has been reduced to a pejorative term among media types (ie: "His speech was all rhetoric and no substance," or what have you...).
Prosody is the rhythm language has. Think poetry. Prosody incorporates not only rhthm, but intonation, meter, flow, stress... that sort of thing. It's what makes language beautiful, simply and artificially.
And another minilesson: pay attention in school. There's way more merit in finding the answer for yourself than there is in siphoning the answer up on an anonymous website where lazy kids get their homework done for them.
(PS: if you copy this word-for-word on your assignment, the homework gods will bash your karma like yesterday's news.)