One of my favorite posts—hope it helps with one of writing’s toughest little questions: When should you use a comma?
Commas are among my favorite tools for building meaning. Used intelligently, commas are wonderful signposts that tell readers which part of a sentence they’ve stumbled into—and then help them make their way out again. I like commas so much I’ve written multiple posts about them.
If comma rules confuse you, take heart! If improving reader comprehension is your goal, there are really only a few “rules” to remember:
Rule 1: After introductory elements.
This is the one most people seem to know about. But I argue that commas are really only necessary when the introductory element gets long enough that readers may miss the lane change back into the main part of the sentence.
After a moment he left the room. (No comma needed unless you want to emphasize a pause.)
After he spent an extended vacation in a remote village in the Alps, where did he go next? (The comma lets readers know that “where” begins a new clause.)
Rule 2: Around or after “interrupters,” including non-essential modifiers (this is a rule, not an option).
I think this one is the most confusing for many writers.
Short interrupters can be easy to spot:
Jane, however, did not go with him to the Alps.
However, Jane did not go.
Non-essential modifiers are elements that can be lifted out of the sentence without compromising its meaning or purpose.
The old car, which was a lot like the one my grandfather used to drive, had been repainted bright blue.
The information about grandad’s car is incidental to the meaning of the sentence, which is that the car is now bright blue. Lift it out and only this incidental information is lost. The rule here, and it IS a rule, is TWO COMMAS, not just the first one. You need that second comma to signal the return to the main clause.
Contrast the example above with this example of an essential modifier, one that can’t be lifted out without eliminating the point of the sentence:
The car that gives you the most mileage is the one you should buy.
Without the modifier, we have:
The car is the one you should buy.
Since the point of the sentence is to say which car, the modifier is essential to the meaning.
NO COMMAS around essential modifiers! They are integral to the sentence, not “interrupters.”
Sometimes confusion about what constitutes an essential or non-essential modifier can turn a sentence into nonsense. I often see commas inserted into constructions like this.
Author Stephen King wrote a lot of books.
Note: no commas. Now try it without the essential modifier, in this case an appositive:
Author wrote a lot of books.
The trick: try taking out the modifying clause and see what remains.
Rule 3: Direct address (this is also a rule, not an option):
Hi, Mr. Smith.
Did you buy bread at the store, Louise?
Louise, did you buy the bread?
Well, Mr. Smith, I guess we won’t be having any bread today.
Rule 4: Before “and,” “but,” etc., if you have more than two items. (This is the infamous Oxford or serial comma.) The elements of the “serial” or list can be words, phrases, or whole sentences.
Louise forgot the bread, cheese, and fruit; she did remember the wine, beer, and vodka.
My worries about her diet involved her lack of protein, her lack of vegetables, and her preference for liquid components.
If you have only two items linked by “and” or “but,” you have a compound and don’t need a comma, as in this sentence, which contains a compound predicate for the pronoun “you.” I’ve underlined the two components (and note the comma after the introductory clause).
Rule 5: Before the “and” or “but” if you’re joining two complete sentences.
I’d argue this is a judgment call, but this sentence illustrates how judicious use of a comma in a compound sentence like this one can tell readers which part of the sentence they’ve ventured into.
That’s five “rules” to absorb—not really so many. Rule Number Six: if one of those five rules doesn’t apply, DON’T INSERT A COMMA. No commas between subjects and their verbs, no commas after “and” or “but,” and so forth. List the five rules and check your questionable comma to see whether one of these applies*:
- After introductory elements
- Around interrupters
- In direct address
- Before “and” or “but” in a list of three or more items
- Before the “and” or “but” in a compound sentence (two complete sentences joined with a coordinating conjunction like “and” or “but”**).
*There are some “conventional” rules for commas that don’t really affect readers’ comprehension, such as the comma that should follow the name of a state (“Austin, Texas, was his home.”) or the ones before and after the year in dates. Any handbook will answer your questions about those minor comma uses.
**There are actually several coordinating conjunctions in addition to “and” and “but,” and the rule applies to them as well, but I didn’t want to muddy the waters too much. The other coordinating conjunctions you’re likely to use include “for,” “nor,” “or,” “yet,” and “so.”