Commas are one of the most commonly used forms of punctuation, and they are also one of the most likely to be misplaced. As a recent New York Times op-ed points out, a couple of centuries ago, people placed the comma wherever they felt like placing it. Nowadays, some have been returning to that “funky comma protocol” as the writer puts it (I love that phrase), but since we now have rules and guidelines about these things, you’re putting your credibility at risk.
Some comma placements are obvious, for example, using the comma to set off dialogue. Others, however, are up for debate or are easily overlooked.
1. Between Independent Clauses
A clause consists of a subject and verb, which forms the basic structure of a sentence. If you have two clauses that work on their own (that is, they are independent), but you think they’d work even better if they were connected, place a comma and a coordinating conjunction with a comma placed in front of it.
You have a choice of six coordinating conjunctions:
“The region serves as a corridor for millions of migratory birds every season, and its variety of habitats host a wide range of hard-to-find local species.”
When the two independent clauses are very short, some grammarians say you can omit the conjunction and use only a comma. On the other hand, if the sentences are lengthier, you’ll be guilty of comma splicing (aka comma abuse) such as the example below:
The project is behind schedule, our communications team has to work late. (Bad grammar!)
2. In a Series
If you’re writing a series of three or more items, you have a choice of whether or not to put a comma before the conjunction connecting the final item.
The Associated Press Stylebook advocates omitting the comma in this instance.
“CIOs need to know what testing strategies, tools and techniques will help them reach their objectives.”
However, the Chicago Manual of Style recommends using it.
“CIOs need to know what testing strategies, tools, and techniques will help them reach their objectives.”
Note: if the items themselves have commas, you might want to use semicolons to separate them.
3. After Introductory Phrases and Words (starting the sentence)
These include the following:
a. Adverbial clauses (describing the action)
“While preparing the report, I made a discovery.”
b. Participial Phrases (begins with an“-ing” verb,“-ed” verb or equivalent for irregular verbs)
“Judging from the new evidence, we may have to make reparations.”
c. Transitional expressions (provides links with previous sentence)
“For example, the company sales have been up despite the economy.”
d. After Interjections, Yes and No
“Yes, we made the deadline” or “Oh, my goodness.”
4. Around Parenthetical or Nonrestrictive Elements
Phrases or clauses that can be omitted without changing the meaning of the sentence are set off from the rest of the sentence by commas.
“Experienced speakers, generally speaking, can handle stage fright.”
“Our chairman, Dwight Holland, changed his mind about the budget.”
5. Between Coordinate Adjectives
How can you check if two or more adjectives describing the same noun are coordinate? Imagine placing“and” between them. If the meaning remains the same, they are coordinate and you can just use a comma to separate.
“It was a dank, gloomy night.”
6. Between Complementary or Contrasting Elements
When two or more of these elements refer to the same word, use a comma to separate them from each other and the rest of the sentence.
The most intriguing, and doubtless most important, aspect of the plan was timing. (complementary)
Patience, not force, is the best tactic. (contrasting)
The more we investigated, the more suspicious we became.
(The two complementary phrases are the entire sentence and only need to be separated from each other.)
7. Between Repeated Words
We need courage, courage to move forward.
So that’s seven tips for the correct placement of commas for some of the trickier instances out there. If you are interested in learning more about comma use and abuse, check out this handy page at the Purdue Online Writing Lab.