Today’s punctuation scenario was probably covered by my post on introductory phrases, but I didn’t specifically address how to use commas with conditional clauses, so here goes.
Conditional clauses start with if. The action in the rest of the sentence depends on the information contained within the conditional clause:
This morning, the battery in my truck died. If my membership has expired, I will rejoin AAA.
In this example, I will rejoin AAA only if my membership has expired. If my membership hasn’t expired, I will not need to rejoin.
If a sentence starts with a conditional clause, use a comma to separate it from the rest of the sentence. You don’t need a comma if the conditional clause is at the end of the sentence. (See how I did that, killing two bird with one stone? How very clever of me!)
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
Fogarty, Mignon, Grammar Girl’s Quick and Dirty Tips for Better Writing. New York: Holt Paperbacks, 2008.