There is probably no more controversial punctuation mark than the comma.
Give three editors the same paragraph, tell them to add commas, and you will end up with three paragraphs in which the commas are all used differently.
The Chicago Manual of Style sums up the issue quite nicely: “Effective use of the comma involves good judgment, with ease of reading the end in view.”
Keeping this in mind, here are seven general guidelines for using comma.
1. Use a comma after opening dependent clauses or long adverbial phrases.
Here’s an example: “If our click-through rate does not improve, we’ll need to revise the content.”
However, a comma is not needed if the introductory phrase is short, such as in this case: “In certain cases we’ll make an exception.”
2. Use a comma to avoid ambiguous or awkward word placement.
“If you are able to practice, try to do so every day.”
“Outside, the police siren shrieked.”
3. Use a comma before and, but, or when it precedes the last term in a series (this is also known as the serial comma).
The serial comma is the most controversial use of the comma. Some writers and editors abhor it; PR Daily embraces it. But the serial comma (or Oxford comma, as it’s also known) serves a greater purpose than dividing people — it’s used to prevent ambiguity.
“Please state name, age, sex, and housing requirements.”
“The patient had hypertension, hyperlipidemia, and anemia, but not hyperglycemia.”
4. Use commas to separate independent clauses joined by coordinating conjunctions (and, but, or, nor, for).
“Would you rather write the company style guide, or be responsible for enforcing the company style guide?”
“Stephen argued that website visitors don’t know what “get a quote” means, and asked us to revise the link.”
5. Use commas to set off parenthetical words, phrases, or expressions.
“The real issue, after all, is how to avoid ambiguity in your writing.”
“Therefore, I was thoroughly disappointed in his first book.”
6. Omit the comma if both independent clauses are short.
“Keep your friends close and your style guide closer.”
“I have read the article and I am concerned about the author’s credibility.”
7. Don’t use commas carelessly.
This one comes from the American Medical Association Manual of Style: “There are definite rules for using commas; however, usage is often subjective. Some writers and editors use the comma frequently to indicate what they see as a natural pause in the flow of words, but commas can be overused. The trend is to use them sparingly.”
Readers . . . care to agree or disagree with any of these rules for commas?