A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

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Part III. Style 20 spelling

Commas are used in a variety of other situations. (For use of commas in dates, see 23.3.1.)

Introductory words and phrases. When you begin a sentence with an introductory element of more than a few words, follow it with a comma, especially if a slight pause normally occurs in speech. A comma is not necessary after a short prepositional phrase unless the sentence could be misread without one.

If the insurrection is to succeed, the army and police must stand side by side.

Having accomplished her mission, she returned to headquarters.

To Anthony, Blake remained an enigma.

After this week the commission will be able to write its report.

Two or more adjectives preceding a noun. Separate two or more adjectives preceding a noun with commas when they could, without affecting meaning, be joined by and. Do not use a comma if the first adjective modifies the second and cannot be omitted without affecting meaning.

It was a large, well-placed, beautiful house.

They strolled out into the warm, luminous night.

She refused to be identified with a traditional political label.

Clarifying comments. Words and phrases such as namely, that is, and for example usually introduce a clarifying comment, so all take a comma after them, and may need a semicolon or period before them. Also, when you use or in the sense of “in other words,” put a comma before it. (These and similar expressions may also be set off by dashes or parentheses; see 21.7.2 and 21.8.1.)

Many people resent accidents of fate; that is, they look on illness or bereavement as undeserved.

The compass stand, or binnacle, must be visible to the helmsman.

Appositives. A word or phrase is in apposition to a noun when it follows the noun and acts like a nonrestrictive clause (see 21.2.3). Such an element is set off by commas. When the appositive is necessary to identify the noun it modifies, however, commas are not used.

Smith, a Reed College graduate, taught at Harvard for several years.

Kierkegaard, the Danish philosopher, asked, “What is anxiety?”

but

The Danish philosopher Kierkegaard asked, “What is anxiety?”

Place-names. Use commas to set off multiple individual elements in names of places. (For commas in addresses, see 23.1.7.)

Cincinnati, Ohio, is on the Ohio River.

The next leg of the trip was to Florence, Italy.

Interjections and conjunctive adverbs. Set off interjections, conjunctive adverbs, and the like to suggest a break in the flow of thought or the rhythm of the sentence. But omit commas when such elements do not break the continuity and do not require a pause in reading.

Nevertheless, it is a matter of great importance.

It is, perhaps, the best that could be expected.

Perhaps it is therefore clear that no deposits were made.

Contrasted elements. Put commas around an interjected phrase beginning with not, not only, or similar expressions only if you intend the reader to pause before the phrase. Use a comma between clauses of the more . . . the more type unless they are very short or might be misread.

The idea, not its expression, is significant.

She was delighted with, but also disturbed by, her new freedom.

The more it stays the same, the less it changes.

Parenthetical elements. Use paired commas when you set off a parenthetical element between a subject and a verb or a verb and its object. If you find yourself setting off more than one such interrupting element in a sentence, consider rewriting the sentence.

The Quinn Report was, to say the least, a bombshell.

Wolinski, after receiving instructions, left for Algiers.

Repeated words. Use a comma to separate identical words. An exception is the word that.

They marched in, in twos.

Whatever is, is right.

but

He gave his life so that that cause might prevail.