Diction—the relative formality of a prose style. Diction is normally of three kinds: high, medium, and low. High diction can be likened to dress; as such it is the “tuxedo” of style. You might find high diction in written laws, contracts, diplomas, official pronouncements, etc. Medium diction (to continue the metaphor) is a jacket-and-tie affair. Most of the language we are exposed to is in medium diction. Essays, newspaper articles, textbooks, and most public speeches are medium diction. Low diction (to beat the metaphor into the ground) is the tee-shirt-and-sneaker approach to language. Our speech with cronies and intimates is often of low diction; we call it being colloquial. In order to make a thematic point or to create a sense of dialect, some literature is in low diction. And yes, that means that vulgarity, obscenity, and the like are beneath low diction. Kind of makes you think.
Tone is at once the trickiest and the most revealing aspect of anyone’s language. Tone is most often described with the same words one would use to characterize a person’s emotional state, e.g., “pensive” “lighthearted” “angry” “sarcastic”. One helpful way to identify the tone of a piece is to ask yourself what mood the speaker seems to be in. Studying word choice and phrasing is a good way to investigate the tone of a work.
Voice is a grammatical term that concerns the origin of action in a sentence. There are two voices, active and passive. “John kicked the ball” is in the active voice. “The ball was kicked by John” is in the passive voice. In an active sentence, the subject of the sentence is the doer of the action; in a passive sentence, the subject of the sentence is the recipient of the action.
Note. The passive voice should be used sparingly, for deliberate reasons.
Mood is another grammatical term. There are three moods: Indicative, subjunctive, and imperative. (There’s also the interjection--Wow! —but let’s not worry about that) The indicative is a statement outright—“It’s time.” The subjunctive is sometimes hard to identify; it relates to statements that are contrary to pure, clean fact: “If I were a rich man” is in the subjunctive mood because the speaker expresses something which may not be true. Note that the verb is in the plural even though the subject is singular. The imperative mood is, of course, the simple command—“Study these terms.” Note that the subject, “you,” is understood and hence omitted.
Subject is the material that you are working with: a book, a project, an individual, etc.
Topic is the particular part of the subject that the writer concerns himself with in the essay. For example, your topic on the subject of the book might be the author’s use of similes, chapter length, the personality of characters, the omnipresence of humor, etc.
Thesis is the particular proposition, or argument, relating to the topic that you advance in a paper. A thesis is a statement of interpretation, as opposed to observation. The thesis is the heart of any critical paper.