Question: What are the most frequent and important uses of the comma?
Answer: After introductory expressions; around “interrupters”; before “afterthoughts.”
After introductory Expressions:
Mr. Jones, will you please answer my question?
Yes, I would be glad to attend.
At the end of July, I was able to arrange….
Rapping her gavel loudly, Shirley called…..
Frightened by the sudden jolt, the child…..
To take good snapshots, you must….
Although he accepted the guilty plea, Judge Smith….
[Note: Introductory expressions have several grammatical names, including “direct address,” “prepositional phrases,” “verbal/gerundial/participial phrases,” “infinitive phrases,” “subordinate clauses,” etc. I have found that the term “introductory expressions” helps to simplify this use of the comma. Grammatical terminology would only add clutter and confusion to the procedure for separating the introductory expression from the rest of the sentence.]
[However, the use of commas after introductory expressions is inconsistent at best in real-world publications. The purpose of the comma after introductory expressions is to prevent confusion with the words that follow, forcing the reader to double-take and re-read the start of the sentence.]
Will you please, Mr. Jones, answer my question?
John Brown, the new captain, spoke to the team…..
He took Mary, who was home from college, to the movies that night.
BUT: "All drivers who go over 55 m.p.h. will be arrested immediately." “…who go over 55 m.p.h.” is not surrounded by commas because it is essential to the meaning. It is not “all drivers” who will be arrested, only “all drivers who go over 55 m.p.h.” That Mary is home from college is not essential, a kind of “by-the-way-did-you-know?” statement. Nonessential clauses and phrases are set off by commas.
[Note: For the same reason—avoiding clutter and confusion—that I included many grammatical terms under the label “introductory expressions” and did not teach the terminology in this context, I include “direct address,” “the appositive” and “relative” or “parenthetical” clauses under the label “interrupting expressions.”
Actually, the biggest problem with “interrupting expressions” is the failure of even experienced writers to use commas both before and after the interrupting expression.]
He lived in Mendham, a town west of New York City.
One’s own judgment is superior to advice, whether it is good or bad.
The vote in America is a substitute for violence, to be defended as one defends civilization.
And somewhere along the line there was a vice-president named Throttlebottom, a good one, too.
[Note: The technical grammatical term for an “afterthought” is an “absolute,” an isolated construction. Many years ago, when people in English worried about defining a “mature” writing style, I read an article suggesting that the outstanding trait of mature writing was the frequent use of absolutes or “afterthoughts.” Absolutes or “afterthoughts” do seem to be plentiful in sophisticated and scholarly materials. ]
In general, these three uses of the comma are most helpful to readers, guiding them in the flow of thought. However, the use of the comma after introductory expressions is inconsistent in real-world publications and the problem with commas around interrupters is to be sure to include commas both before and after the interrupter. The comma before the “afterthought” is consistently used in real-world publications and a possible indicator of mature or sophisticated writing.
I found the expressions “introductory expressions,” “interrupters” and “afterthoughts” in a brief “fill-in” in an old copy of College Composition and Communication. The college, Susquehanna, coined the terms in describing what students had discovered to be the most frequent uses of the comma.