I wrote this treatise on commas for a writing group to which I belonged. It wound up on my university's website, and now it's on mine. You are welcome to print it off once for personal use, provided that you retain acknowledgement of me as author. If you want to link to it or post it elsewhere, just ask permission first.

Now I am noticing a lot of Google hits for specific comma issues. If my examples below do not answer your question about commas, please use my contact form to get the exact information you need. I will reply quickly (if I'm not asleep or teaching), and I will give you the right answer! I won't sell or use your email address, either. Don't hesitate to write.

Whew! So, here it is:

“,” by Seán Dwyer

Ernest Hemingway’s editor complained about his punctuation, so don't be ashamed if people complain about yours. Unless you are Ernest Hemingway, though, you need to improve your punctuation skills. Comma usage is the most challenging punctuation issue.


Rule One: Commas come in pairs
When you make a side comment in the middle of a sentence, you set it off by commas at the beginning and at the end, as if you were using a set of parentheses.

Good:         My brother, the one who used to beat me up, is coming to visit me.
Very bad: My sore knee, which aches when it snows is acting up today.
Very bad: My sore knee which aches when it snows, is acting up today.
Good:         My sore knee, which aches when it snows, is acting up today.
Very bad: The winter weather, however has not kept us from traveling.
Good:         The winter weather, however, has not kept us from traveling. (Or omit both commas.)


Rule Two:  Set off adverbials with a comma or commas
If a phrase that describes an action or a time occurs at the beginning of a sentence, set it apart from the rest of the sentence with a comma. If this phrase is nested in the middle of a sentence, use two commas. If you put these phrases at the end of a sentence, often you cannot use a comma. Do put the phrase as close as possible to the item being modified.

Good:           Sitting in the park, he began to understand why no one liked him.
Very bad:   He caught his breath leaning against a lamp post. Note: This is a quote from a

                       published novel.
Good:           The crowd, staring at the sky, saw the tornado form.
Tolerable:  My cousin ran up to me with a frog, panting.
Good:           Before I went to class, I ate a candy bar.
Good:           I ate a candy bar before I went to a class.
Exception: Before class I ate a candy bar. (With a very short adverbial, you may omit the

                       comma.)

Rule Three: Use commas with non-essential adjective clauses
When you describe a noun with a clause rather than one word, do not use commas if the description sets the noun apart from other similar items. If you are adding parenthetical information, you must use commas.

Good:         My wife, who is from Ireland, speaks four languages.
Very bad: My wife who is from Ireland speaks four languages. (This guy has at least two wives.)
Worse:       My wife, who is from Ireland speaks four languages. (Pair your commas!)
Good:         She went to Florida, which is warm in December. (One comma; the clause ends the

                     sentence.)
Good:         She went to a state that is warm in December. (Clause is essential for clarity, so no

                     comma.)


Rule Four: Use commas for non-essential identifications (appositives)
Names are usually surplus information and should be set off by commas. Some ways of describing people require restrictive phrases, so even names get no commas in these circumstances. Using "the" rather than "a" before a noun means that you are usually talking about a particular item that must be identified, so you don't use a comma.

Good:         Let me introduce you to the mayor of Chicago, Richard Daley. (Exception to "the" rule.)
Good:         Let me introduce you to an influential mayor, Richard Daley.
Very bad: I am going to a reading by an Irish poet Gearóid Mac Lochlainn.
Good:         I am going to a reading by an Irish poet, Gearóid Mac Lochlainn.
Good:         I am going to a reading by the Irish poet Gearóid Mac Lochlainn.
Very bad: I am going to a reading by Irish poet, Gearóid Mac Lochlainn.
Good:         I am going to a reading by Irish poet Gearóid Mac Lochlainn.

Good:         Irish poet Gearóid Mac Lochlainn will read tonight at seven.

Very bad: Irish poet, Gearóid Mac Lochlainn, will read tonight at seven.

Good:         The Irish poet Gearóid Mac Lochlainn will read tonight at seven.

Good:         An Irish poet, Gearóid Mac Lochlainn, will read tonight at seven.


Rule Five: Use a comma before an independent clause that starts with a

                         conjunction
When you could separate two clauses with a period instead of the words "and" or "but," use a comma before the conjunction. If the second clause has no expressed subject, it is a dependent clause, and you do not need a comma before the conjunction. Some authorities think a comma before "but" improves clarity in all cases.

A related issue is the use of a comma with two independent clauses that are not joined by "and" or "but." Don't do it. Use a semicolon.

Good:         I am tired, and I think I will go to bed early.
Good:         I am tired and will go to bed early. (Second clause cannot stand alone.)
A bit bad: They are causing problems and we won't put up with it.
Very bad: Don't wait until finals week to study for your exam, you will not do as well. (Run-on

                      sentence.)
Good:         Don't wait until finals week to study for your exam; you will not do as well. (Use a

                      semicolon.)
Very bad: I am going to visit my grandma, she is eighty years old. (Best turned into two

                      sentences.)
Very bad: I would buy that car but, I think it has transmission problems. (Comma before the

                     “but.”)


Rule Six: Never separate a subject from its verb with one comma
A subject of a sentence, no matter how long it gets once modifiers are added, should never have just one comma added before its verb. (Note that I used two commas around a phrase in the previous sentence.) Some teachers are so adamant about this rule that they give a zero to any paper that has a comma splice.

Good:          A man who was walking down the street in my direction waved to me.
Truly bad: A man who was walking down the street in my direction, waved to me.
Good:          The circus that spent a week in town last month is now in Bemidji.
Horrific:     The circus that spent a week in town last month, is now in Bemidji.
Good:          That circus, which spent a week in town last month, is now in Bemidji.


These rules do not exhaust the possible ways to mess up commas. However, if you get these rules under control, you will take care of 90% of your problems with commas in class papers. Your best next step is to acquire a copy of The Elements of Style by William Strunk Jr. and E.B. White and learn it from cover to cover.

© 2006 by Seán Dwyer. All rights reserved.

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