When to use a comma in a series

Summary:

This resource offers a number of pages about comma use.

The comma is a valuable, useful punctuation device because it separates the structural elements of sentences into manageable segments. The rules provided here are those found in traditional handbooks; however, in certain rhetorical contexts and for specific purposes, these rules may be broken.

The following is a short guide to get you started using commas. This resource also includes sections with more detailed rules and examples.

Writers frequently wonder whether a comma should go before the conjunction and in a list of three or more items. Despite the fact that not all style books agree on this issue, we recommend using a comma after the next-to-last item in a series—the serial comma, as it is called (or the Harvard or Oxford comma).

This recommendation also applies, of course, when the items in a list are joined by the conjunction or.

The Serial Comma Helps to Prevent a Misreading

Although many of us were taught not to use a comma before and in a list, today the vast majority of style guides do advocate the use of the serial comma because it can prevent a possible misreading. Consider this sentence, for example:

• Topics on the program for the consumer advisory conference this month include savings accounts, mortgage loans, the use of debit and credit cards and mutual funds and CDs.

Without the serial comma, the individual series items are difficult to identify.

• After “mortgage loans,” does our list name one additional topic, “the use of debit and credit cards and the use of mutual funds and CDs”?
• Or does it contain two more items, “the use of debit and credit cards” and “mutual funds and CDs”?
• Or does it contain three more items, “the use of debit and credit cards,” “mutual funds,” and “CDs”?

With the serial comma added, we can see clearly that we have here a list of four program topics, not two or three:

Topics on program for the consumer advisory conference meeting this month include savings accounts, mortgage loans, the use of debit and credit cards, and mutual funds and CDs.

Although such logical precision might seem trivial when we are talking about topics at a conference, it can be absolutely crucial in certain kinds of writing.

The Serial Comma is Especially Important in Legal Writing

Take legal documents, for example. The Texas Law Review Manual on Usage, Style, and Editing  insists on the use of the serial comma. In The Lawyer’s Book of Rules for Effective Legal Writing, Thomas R. Haggard says, “The serial comma is essential in legal writing because it promotes clarity” (17).

Consider this sentence:

Mrs. Jones left all her money to her three children: Huey, Dewey and Louie.

Without the serial comma, the sentence does not clearly indicate that each of the three children is to be given an equal share of the inheritance. Quite possibly (especially if Huey were a jerk), Huey would get half the money, and Dewey and Louie would have to split the other half.

Here’s another example of a sentence in which the omission of the serial comma has a substantive effect on the meaning:

Mrs. Jones left her money to her children: Sally and Fred Smith, Margaret and John Williams, Betty and Harold Spivey and their children.

Without the serial comma before the last and, the sentence could be interpreted to mean that only the children of Betty and Harold Spivey are to receive a share of the inheritance and not the children of the other couples. But with the additional comma, the sentence more clearly communicates the idea that the children of all three couples are to receive a share:

Mrs. Jones left her money to Sally and Fred Smith, Margaret and John Williams, Betty and Harold Spivey, and their children.

In all kinds of writing, of course, the meaning of the items in a list may be obvious without the serial comma. But we are usually poor judges of our own clarity (or lack thereof). We tend to think we are being clear because we know what we mean to say.

If we were to write, for example, “The table was covered with gifts, food and flowers,” the meaning might appear to be quite clear without the serial comma.

But even this seemingly simple and clear sentence could be read two ways:

• The table may be covered with three different kinds of items: (1) gifts, (2) food, and (3) flowers.
• Or the table may be covered with gifts, all of which fall into one of two categories—food or flowers.

Not All Style Books Agree

It is always wise to check your company’s in-house style manual or the style manual that governs your profession. In the United States, the vast majority of reputable style guides (with the exception of style guides for journalists, such as the well-known manual published by the Associated Press) encourage or even mandate the serial comma.

We don’t know for certain, but we can suppose that print journalists omit the serial comma because in the early days of their profession, when most news was still delivered in print, saving keystrokes meant saving money.

But even style guides that generally discourage its use do agree that at times it is necessary for clarity and/or readability.

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