Last week in this column, we discussed how to use commas when two independent clauses are joined by a conjunction. Well, dependent clauses sometimes need commas, too.
Dependent clauses, remember, look a lot like sentences in that they contain a subject, a verb, and often a direct object, but they can’t stand alone as complete sentences. When a dependent clause comes before the main clause in a sentence, it should be followed by a comma. The previous sentence itself is an example of what I’m talking about, but here’s another for good measure:
If it rains again today, Los Angeles will have seen a week of wet weather.
When a dependent clause comes after the main clause in a sentence, do not use a comma if it is restrictive—i.e., the main clause won’t make sense without it. This sentence, too, serves as an example—see how I’m doing that? (Let’s see if I can keep it up!)
Take an umbrella because it looks like it is going to rain again today.
Do use a comma, however, when a nonrestrictive dependent clause follows the main clause in a sentence—that is, if it contains supplementary or parenthetical information that is not essential to understanding the sentence. (Couldn’t do it with that one—I’d love to hear your suggestions!)
It could rain every day for the rest of the month, if you ask me.
Whether to use a comma when a dependent clause follows the main clause is sometimes a matter of judgment. When in doubt, use a comma to signal a pause.
Now for a scenario so bothersome to me that I wrote an entire post about it early in the early days of this blog. When a dependent clause is preceded by a coordinating conjunction so that two conjunctions end up next to each other—i.e., and if, but if, etc.—do not separate them with a comma if the dependent clause is restrictive:
The clouds are supposed to clear by the weekend, and if the weather report is right, we will go to the zoo on Saturday.
For a much more detailed exploration of this topic, check out my previous post.
Do you have a question about the comma? Let me know, and I’ll include it in a future installment of Mots Justes’ ongoing series.
The Mots Justes Series on Commas
Chicago Manual of Style, The. 15th ed. Chicago: The University of Chicago Press, 2003.
Hacker, Diana, The Bedford Handbook for Writers, 3rd ed. Boston: St. Martin’s Press: 1991.