Most of us recognize that the comma is perhaps the most difficult piece of punctuation to get right because it has so many rules that apply to it. I prefer to call them conventions instead of rules because their usage is determined more by standard practice that has evolved over time rather than by someone dictating the rules of their use. Commas, like all punctuation, follow currently established conventions that may change with time. (See the article link at the end of this post.)
My intent in this post is not to explore the many uses of the comma but to concentrate on a few of the stumbling points of comma usage.
Here’s an interesting point: with only a couple of exceptions, commas occur in pairs. Now, before you raise an objection, I want to say that sometimes the second comma in a pair is invisible because it would occur either at the beginning or end of a sentence.
Let’s look at a couple of examples. A comma is used when addressing a person in dialogue and surrounds the person’s name:
—“Tell me, Michael, where you were today.”
—“Michael, tell me where you were today.”
—“Tell me where you were today, Michael.”
In the first sentence, “Michael” is being addressed directly, so we set off his name with a pair of commas, but in the second and third sentences, his name comes first and last respectively, so the second comma disappears. In the third sentence it’s absorbed by the period.
This same principle applies to words and phrases offset in sentences:
—However, I may stay home today.
—I may, however, stay home today.
—Because it’s cold outside, I will wear warm clothing.
—I will, because it’s cold outside, wear warm clothing.
The exceptions to this comma pairing occur whenever we have a series. In that case, a comma separates each item in the series and the commas do not occur in pairs:
—She was wearing torn, faded, black, boot-cut jeans.
—She decided she would get her car washed, go shopping, come home, and watch TV for the rest of the afternoon.
(For those of you who feel that the comma before “and” is unnecessary—a controversy that has raged for years—the Chicago Manual of Style (CMOS) now recommends putting it in.)
With that behind us, let’s get to a couple of the stickier problems with comma placement.
(1) Commas may precede but rarely follow conjunctions
I see a number of writers put a comma AFTER conjunctions like “and” and “but.” The following are INCORRECT:
—But, he didn’t want to go with us.
—And, she objected to our choices.
—We made our choices and, she objected to them
—Bill and Tom did not go to the mall like they said they would but, instead went to see the latest Avengers movie.
In the first two sentences, no comma should be used. In the second two, the comma comes BEFORE the conjunction (and, but).
(2) Commas with parentheticals
Parenthetical expressions are basically extra information added into a sentence. As such, the expression can be omitted without changing the sentence meaning. Sometimes these parentheticals are put in actual parentheses, and sometimes they’re separated by commas. What’s important is to be sure the commas are placed correctly:
—Last winter was a harsh one. I saved a lot of money on gas, because in the snowy weather, I didn’t drive around as much. [WRONG COMMA PLACEMENT]
The problem in that sentence is that the actual parenthetical is “in the snowy weather” not “because in the snowy weather.” The easy way to determine this is to take out the expression within the commas. If the sentence doesn’t make sense, then the commas are in the wrong spot:
—Last winter was a harsh one. I saved a lot of money on gas I didn’t drive around as much. [THIS SENTENCE DOESN’T MAKE SENSE.]
The correct comma placement is this:
—Last winter was a harsh one. I saved a lot of money on gas because, in the snowy weather, I didn’t drive around as much.
If you remove the parenthetical, the sentence now makes sense:
—Last winter was a harsh one. I saved a lot of money on gas because I didn’t drive around as much.
And I want to point out that the commas could be left out entirely because the sentence works just as well without them. However, when the parenthetical is longer than just a simple prepositional phrase, the commas are usually required for clarity, and it’s important to place them correctly.
It’s just as important to make sure the commas are truly needed. Some of the comma “rules” would have you add commas that, while technically correct, could result in overloading the sentence with unnecessary commas.
There’s one case where sometimes the first comma may be omitted with parenthetical and other phrases. This case avoids comma clutter. Look at the following sentence:
—Jack finished running his usual one mile, but, because he wasn’t tired, he decided to run another.
The comma before “but” is required because we’re joining two independent clauses with a conjunction. We would normally also insert a comma AFTER both “but” and “tired.” The phrase “because he wasn’t tired” follows the rule given above as one that can be taken out without changing the sentence meaning and should be enclosed with commas. However, the comma before and after “but” looks strange, even though both are technically correct. Another rule in the CMOS says that short phrases like that can omit the comma before it (the one after “but”):
—Jack finished running his usual one mile, but because he wasn’t tired, he decided to run another.
You’ll agree that this looks better. If you really feel you want that extra comma, you can insert it, but I’d advise instead that you recast the sentence to avoid that ugliness of the extra comma:
—After he finished running his usual mile, Jack wasn’t tired and decided to run another.
When it comes to placing commas, many times they fall where you would pause while reading, but just because you feel you should pause, don’t insert a comma unless you can find proper justification for inserting it. Above all, avoid clumsy-looking sentences.
Now, in case this post wasn’t enough for you, here’s an interesting bonus article I found: