There is probably no more controversial punctuation mark than the comma.
Have three editors tackled a paragraph that is devoid of commas, and you will probably end up with three pieces of text in which commas are used very differently.
“The American Medical Association Manual of Style” sums up the issue quite nicely:
“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.”
So keeping in mind that comma use can be subjective, here are five general guidelines about its use:
1. Use a comma after opening dependent clauses or long adverbial phrases.
Here’s an example: “If the infection recurs within two weeks, an additional course of antibiotics should be given.”
However, a comma is not needed if the introductory phrase is short, such as in this case: “In some patients the medication causes sleepiness.”
2. Use a comma to avoid ambiguous or awkward word placement.
• “Patients who can exercise, try to do so every day.”
• “Outside, the ambulance 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 punctuation. 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 is used to prevent ambiguity. For example:
• “The physician brought a copy of the medical record, a journal article, and a textbook to the deposition.”
• “The physician, the nurse, and the family could not persuade the patient to stay in the emergency department.”
• “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).
• “The patient’s condition was unchanged after the first medication, but the second medication resulted in a marked improvement.”
• “No credible experts could be identified, and the differences of opinion between those who reviewed the case were so great that no real comparison was possible.”
5. Use commas to set off parenthetical words, phrases, or expressions.
For example: “The real issue, after all, is how to avoid ambiguity in your writing,” or, “Therefore, I was disappointed in his latest book.”
6. Omit the comma if both independent clauses are short.
• “The test might be useful or it could be harmful.”
• “I have read the article and I am concerned about the author’s objectivity.”
7. Don’t use commas carelessly.
This one comes from Lynne Truss, author of “Eats, Shoots & Leaves”: “More than any other mark, the comma requires the write to use intelligent discretion and to be simply alert to potential ambiguity.”
PR Daily readers, care to agree or disagree with any of these rules for commas?
Laura Hale Brockway is a medical writer and editor from Austin, Texas. She is also the author of the writing/editing/random thoughts blog, impertinentremarks.com.