Two commas, not one: Comma-Delimited Lists in Writing

Recently I’ve been reading more articles than I normally do, and besides the underlying thread of technology there is another common aspect I have realized when reading these articles: (relatively) poor grammar. And it’s not just on some of the out-of-the-way blogs that I’ve seen this, but on blogs like sofaMoola—a great blog about making money on the internet and the authors’ stories of doing so—and even some of the more popular blogs like Lifehacker.com. It’s not a big deal, but it’s enough to annoy me. The common mistake: a single comma.

So a little background. I would say the split is around 50-50, so it won’t be something you see on most blogs, nor will it be something you see infrequently. However, it is fairly common to see a sentence formed like this: “I like milk, cheese and eggs,” with the author thinking that this is perfectly acceptable. Well, it isn’t. Think of it this way: every item in the list, for that is what that is: a list of items that our hypothetical person likes, is separated by a comma. For lists of two items, a simple “and” goes between the two items. Example: “I like apples and oranges.” However, when three or more items are part of the list, a comma is introduced between the first and second item, and before the “and” preceding the last item. Example: “I like milk, cheese, and eggs.” Notice that this sentence can be differentiated from the similar sentence at the beginning of this paragraph by the comma between “cheese” and “and eggs”. So why the third comma? There are two explanations to this: the easy one, and the more complicated and comprehensive explanation. First, then, the simple explanation.

Simply put, a comma-delimited list such as the one above—“I like milk, cheese and eggs.”—(this is the incorrectly formatted sentence) actually consists of two items, not three. In actuality, our hypothetical person is saying, in this sentence, that he or she likes milk, and that he or she also likes cheese and eggs mixed together. The second, correctly formatted sentence—“I like milk, cheese, and eggs.”—explains how our hypothetical person likes three different things: milk, cheese, and eggs—each a separate food item. Think of it this way: the number of things this person likes is the number of commas +1, so in the first sentence there is only one comma, so therefore there can only be two things that he or she likes; however, in the second sentence there are two commas, and therefore there are three things that he or she likes.

Take another sentence to help solidify this example: “I would like a milkshake with fudge on the bottom, vanilla in the middle and chocolate on top.” This sentence sounds fine if you say it and even when you read it, although it is, in fact, incorrect. Our newfound milkshake sentence implies that the person asking for the milkshake wants one with fudge in the bottom, vanilla in the middle, and chocolate on top of the vanilla middle, not actually on the top of the milkshake—the top of the milkshake is left undefined. For example, you could say this: “I would like a milkshake with fudge on the bottom, vanilla in the middle, and chocolate on top.” This second sentence asks for a milkshake with fudge on the bottom, vanilla in the middle, and chocolate as a topping to the milkshake. In this sentence, all aspects of our milkshake are defined, and those of us with a programmer’s mindset can walk away from the window happy.

Now then, the more in-depth explanation. To really understand this, you must think back to something I’m sure many of you have blocked from your memory: sentence diagramming. Sentence #1 is going to be “I would like a milkshake with fudge on the bottom, vanilla in the middle and chocolate on top.” Sentence #2 will be “I would like a milkshake with fudge on the bottom, vanilla in the middle, and chocolate on top.” For brevities sake—and mine—I am only going to include the part that describes the milkshake—in the first sentence, this would be “…fudge on the bottom, vanilla in the middle and chocolate on top.” and in the second this would be “fudge on the bottom, vanilla in the middle, and chocolate on top.”

The first sentence diagrammed:

And the second sentence:

Technically, in each case there should be an “and” connecting the branches of the diagram, but I have simplified this example in order to focus on only the aspects relating to this article.

Notice that in each diagram, there are a few different branches. In the first diagram, there are two main branches in red, with three spaces for words atop the gray branches. In the second sentence, there are three main branches again in red, with the three spaces for what are in this case adjectives atop the gray lines. Think of each red line—main branch—as a separate item. When thought of this way, it is easy to see that in the first sentence that only features a single comma—“…fudge on the bottom, vanilla in the middle and chocolate on top.”—only has two separate items, whereas the second sentence with the two commas actually features three separate items.

Like I said earlier, you can use this little cheat to help with deciding how many commas you should be using: “the number of things this person likes is the number of commas +1,” or in a more general way: for a list of x items so that x > 2, you should have x-1 commas. A few final examples:

• Two items: I like eggs and cheese. (No commas because there are only two items)
• Three items: I like apples, oranges, and grapes. (Two commas since there are three items: 3 > 2 and 3-1=2)