Before examining the final comma function, let’s review the running list of essential comma functions:

1. Commas show slight pauses.

2. Commas set things off from the main line of a sentence.

3. Commas show a slight drop in pitch.

There’s still one more comma function left for us to explore, and in a sense, it’s the most essential function. Here it is, in all its grand complexity:

Commas separate things.

We have explored how commas separate modifying elements (words, phrases, and clauses) from the main line of a sentence. In a very general sense, when I say, “Commas separate things,” I could mean that such separations include the divisions between those modifying elements. With functions 1 and 3 in mind, I could mean that commas separate things (like modifying elements) by representing slight pauses and drops in pitch. So, in this general sense, the notion that  “commas separate things,” serves as the all-encompassing comma function.

In this article, though, I intend this rule in a very specific sense. With that in mind, I will modify the rule a bit:

Commas separate items to show that they are to be considered as individual things.

Commas Separate Items in Lists

This function applies when we use commas to separate items in a list (also called, “items in a series”). Consider the example below:

The series on apostrophes explores possessives, contractions, and s-ending nouns.

Notice the commas in the sentence above. They act as visual guides to the reader, to express the notion that the three items are separate and distinct from one another, but that they are still connected in the sense that they are all explored in the series on apostrophes. (Paradoxically, the comma combines things, even as it divides them.) If the sentence is spoken, those commas become pauses that allow the listener to hear the separations.

But are these commas necessary? After all, the reader could get by without the aid of those commas in determining that the items are separate. Here is the sentence, without the commas:

The series on apostrophes explores possessives contractions and s-ending nouns.

Even if we can perceive these separations without the help of dividing commas (and I think most readers can, with varying degrees of effort), this second sentence requires more thinking on the part of the reader—and it’s not the kind of thinking we want readers to do. It makes the reader do a double-take. Yes, the reader can get by. However, getting by is most assuredly not what we want for our readers. We want to serve our readers with prose that guides them smoothly and seamlessly through our ideas and assertions. If readers do not feel well served, they will turn away from our writing and find something better to read. And that’s the last thing we want.

Although I discuss them here as an element that writers use to serve readers, such dividing commas are not merely a matter of preference. The use of dividing commas is a set-in-stone rule of writing. However, it is also a tried-and-true rule, one that exists for good reason: clear communication.

In some cases, separating commas are absolutely necessary to the meaning of sentences. In such situations, the reader cannot even manage get by in understanding the prose’s essential message. For example, consider this sentence:

I enjoy experiencing movies and writing.

What am I saying here? Am I saying that I enjoy three acts (experiencing, movies, and writing), or that I enjoy two acts (experiencing movies and experiencing writing)? There is yet another possibility: I could be saying that I enjoy (1) the act of writing and (2) the act of experiencing movies.

Which of these three messages do I intend? Without the aid of commas, there is no way to know for sure. The reader, if given no clarifying context, has no way of knowing for sure what this sentence states. She is left with three possibilities. As she continues to read, she can only ponder which possibility she is reading about in later sentences and paragraphs. (Think about that: the lack of commas causes harm, not only in the example sentence, but the sentences and paragraphs that follow it.) What reader wants that?

In addition to separating items in lists, commas separate other things. Commas separate elements within a date, specifically the day of the month and the year:

Christopher Altman’s birthday is November 18, 1977.

(Note: Do you hear the pause between “18″ and “1977″? Do you hear the slight change in pitch?)

(Additional Note: November 18 is my actual birthday. Mark it on your calendar and send me a present when that date rolls around.)

Commas Make Long Numerical Expressions Easy to Read

Commas also serve a very important function in writing large numbers: they separate numbers into sets of three digits to help the reader differentiate between large number groups like millions, billions, trillions, and so on. Here is an example of a number without commas:

Over the course of the last fiscal year, the company earned $40927943.00.

Ugh. That’s hard to read. Now, try this one:

Over the course of the last fiscal year, the company earned $40,927,943.00

Unless you are very good with numbers, I expect you had a great deal of trouble figuring out if that first number was in the 40 millions or the 400 millions. In fact, I’ll wager that many readers attempting to identify that comma-less number would identify it by mentally grouping the numbers, from right to left, into sets of three. The comma does that for the reader, allowing her to know the identity of large numbers, at a glance. Yet again—even with numerical expressions—the comma functions to serve our readers.

As a courtesy to our readers, we should apply this rule even to easy-to-read four-digit numbers:

Bob, an adjunct English instructor, earns about $2,300.00 for each course he teaches.

Commas Precede Coordinating Conjunctions to Combine Two Sentences

The last use of the comma’s dividing function I will discuss has to do with coordinating conjunctions. Commas should come before coordinating conjunctions whenever the coordinating conjunctions combine two complete sentences. (Coordinating conjunction examples: and, but, yet, so, or, nor, etc.)

Here is an example:

Last year, Bob taught three literature courses, and he served on the department’s hiring committee.

Notice that I am using “and” to combine two complete, stand-alone sentences:

1. Bob taught three literature courses

2. He served on the department’s hiring committee.

The comma acts as a dividing agent, in that it adds additional force to the conjunction “and.” It says to the reader, “I am combining two big things here—sentences that could stand alone. Beware, reader: this single sentence involves, not one, but two complete (but related) messages.” It says, “Pause before this ‘and‘ to recognize that you are about to read another complete, stand-alone idea.”  All that—from a comma!

Here is a sentence that expresses the same essential idea. Notice, though, that it does so with the use of a compound verb:

Bob taught three literature courses and served on the department’s hiring committee.

Now, notice that there is no comma before “and.” That is because “and” is not combining two complete sentences. It combines two verb phrases:

Bob . . .

1. taught three literature courses

and

2. served on the department’s hiring committee

The presence (or lack) of a comma in the sentences above acts as a visual cue to the reader to know what is to come in the sentence.

Well, that’s it for comma functions—almost. Before moving onto other things comma, we should explore one more consideration about comma functions: are comma functions ever at odds in sentences? Can that cause confusion for readers? To find out, read the next article, “When Commas Collide: Confusion over Closely Placed Commas.”

Here is the link:

• When Commas Collide: Confusion over Closely Placed Commas

Christopher Altman, a community-college composition specialist, is passionate about bringing the art of effective writing to average, everyday Americans. He has published work in the field of medieval literature, and has authored a book on advertising language entitled, Telling the Truth to Deceive: How Advertisers Manipulate the English Language. Mr. Altman is an assistant professor of English at Onondaga Community College in Syracuse, New York.