The Serial Comma

So what is the serial comma? The serial comma (also known as the Harvard comma and the Oxford comma) is the comma placed between the second-to-last item in a list and the coordinating conjunction (and, or, nor).

We solved the equation for x, y, and z.  (with serial comma)

We solved the equation for x, y and z.   (without serial comma)

Both of these sentences are grammatically correct, although there is a long standing debate on the correct usage. Most style guides for academic writing require or recommend the use of the serial comma to avoid potential ambiguity.

Read on to learn about how to use the serial comma, or jump straight to testing your knowledge on a short quiz.

Learn more…

Listed below are some of the style guides that require use of the serial comma.

---

1. The American Medical Association, Manual of Style, 9^th Edition, 1998, Chapter 6.2.1:

Use a comma before the conjunction that precedes the last term in a series.

• Outcomes result from a complex interaction of medical care and genetic, environmental, and behavioral factors.
• The physician, the nurse, and the family could not convince the patient to take his medication daily.
• While in the hospital, these patients required neuroleptics, maximal observation, and seclusion.

---

2. Council of Biology Editors, Scientific Style and Format, 6^th Edition, 1994, Chapter 4.15.6:

To separate the elements (words, phrases, clauses) or a simple series of more than 2 elements. A comma should precede a closing “and” or “or.” This rule applies to adjectives each modifying the following noun.

• The tomatoes, beans, and peppers were planted in April.

---

3. American Psychological Association, The Publication Manual, 5^th Edition, 2001, Chapter 3.02:

Use a comma between elements (including before and and or) in a series of three or more items.

• the height, width, or depth
• in a study by Stacy, Newcomb, and Bentler

---

4. Council of Science Editors, The CSE Manual for Authors, Editors, and Publishers, 7^th Edition, 2006, Section 5.3.3.1:

To separate the elements (words, phrases, clauses) of a simple series of more than 2 elements, including a comma before the closing “and” or “or” (the so-called serial comma). Routine use of the serial comma helps to prevent ambiguity.

---

5. Chicago Manual of Style, 14^th Edition, 1993, Chapter 5.5:

In a series consisting of three or more elements, the elements are separated by commas. When a conjunction joins the last two elements in a series, a comma is used before the conjunction . . .:

• Attending the conference were Farmer, Johnson, and Kendrick.
• We have a choice of copper, silver, or gold.

---

Although you should be consistent in your use of the serial comma within one document, it is even more important to write clearly.

Example 1

Which elements are linked in the following sentence?

The compound is soluble in hexane, methanol and water and acetone.

In this sentence, it is unclear whether “methanol and water” or “water and acetone” should be grouped together. This ambiguity can be resolved by using the serial comma.

The compound is soluble in hexane, methanol, and water and acetone.

Meaning: The compound is soluble in hexane. The compound is soluble in methanol. The compound is soluble in water and acetone.

Alternatively, the meaning of original sentence can be made clear by REARRANGING the list, either with or without the serial comma.

The compound is soluble in water and acetone, hexane, and methanol. (with serial comma)

The compound is soluble in water and acetone, hexane and methanol. (without serial comma)

Example 2

Sometimes a sentence can be ambiguous regardless of whether or not a serial comma is used.

The conference was attended by Professor Smith, a Nobel Prize winner, and the president of the university. (with serial comma)

The conference was attended by Professor Smith, a Nobel Prize winner and the president of the university. (without serial comma)

In the sentence with the serial comma, it is unclear whether the sentence refers to one person (Professor Smith, who is a Nobel Prize winner and president of the university), or three people (Professor Smith; a Nobel Prize winner; and the president of the university).

In the sentence without the serial comma, it is unclear whether the sentence refers to two people (Professor Smith, who is a Nobel Prize winner; and the president of the university), or three people (Professor Smith; a Nobel Prize winner; and the president of the university).

In this case, in order to make the meaning clear, the sentence should be REARRANGED as follows.

Professor Smith, a Nobel Prize winner and the president of the university attended the conference. (three people)

The conference was attended by Professor Smith—a Nobel Prize winner—and the president of the university. (two people)

The conference was attended by Professor Smith—a Nobel Prize winner and the president of the university. (one person)

For more information on the serial comma, refer to the Wikipedia page on the subject: http://en.wikipedia.org/wiki/Serial_comma