Writing & Grammar: Do You Need a, Comma?

by Jennie Ruby  

Do I need a comma after "In 2008"? That is one of the most frequent questions I am asked in grammar classes. The answer I must give is that the comma is usually optional. For seekers of definitive answers with which to mow down the opposition, this "optional" nonsense is an unacceptable situation. So for them, and for you, if you are seeking definite answers, I must dig deeper.

First, let's distinguish the particular kind of introductory element for which the comma is "optional." But before even doing that, let's define "introductory element"!

An introductory element is a word, phrase, or clause that is placed before the beginning of the sentence. We have to make sure something is "introductory" before throwing commas at it. Here are some examples of introductory elements. In each case, we have a complete sentence even if we remove the introduction:

• Tomorrow, we must weed the garden. [comma optional]
• On Thursday, the trash truck ran over the mailbox. [comma optional]
• After the game, the kids ran to the convenience store to buy energy drinks. [comma optional]

Here are some examples of those same words and phrases used not as introductory elements, but as part of the sentence:

• Tomorrow was always her focus.
• On Thursday is when we plan to hold the kick-off meeting.
• After the game will be a good time to ask for a signed photograph.

In each of these sentences, we have a complete sentence only if we include the first word or phrase; the first word or phrase is actually the subject of the verb.

All of the examples above are one-word adverbs(tomorrow) or short prepositional phrases of time or place. These are the particular kinds of introductory elements for which most grammar guides say the comma is optional.

Most, but not all--I do have one grammar book on my shelf that simply states: Use a comma after every introductory element. But all of my other principal references--the Chicago Manual of Style, the Gregg Reference Manual, and Abrams' Guide to Grammar--say that the comma is optional after one-word adverbs and short prepositional phrases of time or place. And what counts as short? Fewer than five words.

So if these references tell us the comma is optional, how do we decide whether to use it or not? Your in-house style guide may clear this up for you. As an organization, you can decide whether to require the comma, or to forbid that comma, or to leave the decision up to each writer or editor on a case-by-case basis.

Check your in-house style guide (you have one, right?), and then tell me whether a comma is needed in these examples (be careful-they might not all be the kind of introductory element discussed above!): 

1. After the sudden afternoon rainstorm three kids were rescued from a flash flood.
2. Before noon we had already covered all of the class material.
3. In 2010 our outreach program was updated to include a Twitter feed.
4. Sometime after 2012 is when support for version 3.5 will end.
5. Unless the creek floods we will go kayaking tomorrow.
6. By the end of the session we all understood introductory elements.
7. Yesterday the website was down for an hour.
8. Tomorrow is our deadline for completing these two modules. 

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