Next time you wonder whether to use one comma or two to set off a word or phrase in the middle of a sentence, imagine reaching in and lifting that word or phrase out with both hands. Does the sentence still make sense? If so, lower the text back in, and put commas in place of your hands.
For example, you need both commas in all of these sentences:
- Fruit flies, for example, can breed up to ten times an hour.
- The TV, however, sat idle.
- The house that Sandee likes, the one with the striped curtains and the funny gargoyle on the second story, went up for sale last week.
With certain types of words, the second comma goes missing especially often. For example, even though most style guides would call for commas on each side of the following bolded words (right where you’d put your hands), many writers would use only the first comma.
- Macy’s, Inc., made headlines today.
- The plane will land in Portland, Maine, right on time.
- Rodney, Jr., has a birthday coming up.
- The letter dated January 2, 1987, changed George’s life.
I’m not sure why second commas get omitted so often. Leaving out half of a comma pair is like leaving out a parenthesis. You wouldn’t do that (would you?