When to use commas (or not use them) is a common frustration among writers. It’s important to remember that the overall goal of the comma is to increase readability, or the ease of reading. They denote a slight pause in the reading. Therefore, regardless of the rules of commas, put it commas that increase understanding of your meaning and remove ones that detract from it.
The following rules are based on Chicago Manual of Style (CMOS), which is the style guide used for fiction. Other style guides may have slightly different rules. However, if you follow these rules regardless of the type of writing, you’ll be in good shape, and your copyeditor or proofreader can change any minor differences to conform with the appropriate style guide.
Setting Off Elements from Surrounding Text
Certain elements in writing are nearly always set off by pairs of commas—one before the element and one after. Examples of these elements are a state’s name and a year when used in conjunction with a month and day.
The aquarium in Atlanta, Georgia, is a worthwhile attraction to visit.
In the example above, the state is set off by a pair of commas. One comma comes before the state, and one comes after. The comma after may look odd to some because there’s nothing that would otherwise require the comma there, but that’s the rule—states always have a comma before and after, regardless of the state’s position in the sentence.
However, complete addresses are written differently:
At 25 Capitol Ave., Atlanta, GA 30225, you can request a copy of the state’s audit report.
Note that there’s no comma after the state in this example, when a full address is given. Instead, the comma comes after the zip code.
This rule about pairs of commas also applies to countries:
I am looking forward to my trip to London, England, later this year.
Dates are similar.
November 22, 1963, will long be remembered by Americans; it was the day President John F. Kennedy was shot and killed.
This example for a date shows that when a full date (month, day, and year) is given, the year is always set off by a pair of commas. Again, the comma after the year may look odd, but just like with states, the rule is that the year is always set off by a pair of commas even if there’s no other reason for a comma to be there. On the other hand:
November 2019 was special to us; it was the first time we spent Thanksgiving with our friends—our chosen family.
The 2019 Christmas pageant was exceptional.
In both of the examples above, the full date with month, day, and year is not used, so a comma is not needed to set off the year.
Commas for Items in a List
Commas are used between items in a list. CMOS calls for the use of a comma before the conjunction (e.g., and, but, or) in a list of three items or more. This last comma is called by many names: serial comma, Oxford comma, and Harvard comma. All of these are the same thing; they’re just called by a different name depending on the company you’re with. Here’s an example of the serial comma in use:
I have mandarin oranges, red apple slices, and green grapes in my fruit cup today.
Without a serial comma, it would look like this:
I have mandarin oranges, red apple slices and green grapes in my fruit cup today.
Commas in a list also apply to actions rather than items:
I vacuumed the carpet, swept and mopped the kitchen floor, and cleaned the windows today.
The serial comma is a hot topic and has even resulted in a court case due to misinterpretation from a lack of a comma.
The serial comma is an area where style guides differ. For example, CMOS calls for the serial comma, but The Associated Press Stylebook (AP Stylebook), which is typically used for newspapers and magazines, does not. My understanding is that the primary reason the AP Stylebook doesn’t use it is because, in those mediums, space is always short; therefore, any punctuation is omitted if it’s unnecessary for clarity.
I strongly prefer the use of the serial comma. Sometimes it’s confusing to the reader whether the last two items in a list (particularly if it has more than three elements) are meant to be one thing. Since you’re writing it and know exactly what you meant, you may not see it as confusing, but readers may interpret it differently. It’s much easier to just always use the serial comma rather than trying to spend the energy figuring out if it could be read differently than intended. There’s never a downside to using the serial comma because it always makes the intentions clear. But there’s a big potential downside if there’s confusion due to the lack of the serial comma (see court case linked above).
It seems there’s always an exception to every grammar rule, and this one is no different. If you use an ampersand (&) instead of the word and, such as in company names, there is no comma before the ampersand.
I use the CPA firm Nevin, King & Dugan for my taxes.
Note that there’s always a comma between all the items in a list except for possibly the last two (depending on the style guide and whether there’s an ampersand). The commas for all but the last two items are not debatable in any situation.
Commas aren’t your thing? I can help!