The other week, I introduced commas, semi-colons, and colons by briefly introducing their functions. For the sake of brevity (ha), I left it there, so today we’re going to focus in-depth on commas. Commas do a lot, so we’re only going to focus on these four important functions:
- separating items in a list of two or more
- forming a compound sentence when joined with conjunctions
- offsetting modifiers and dependent clauses
- offsetting clauses that interrupt the main thought of a sentence
Let’s take a look at each of these functions individually – even though, of course, you may end up with many sentences in which commas are used in more than one way.
(For more detailed information about comma usage, see Purdue’s Extended Rules for Commas.)
Commas separate items in a list of two or more.
Edna devoured the sight of cursed necklaces, good luck charms, and cracked cauldrons used for potion-making centuries ago.
So, the Oxford comma. I obviously can’t talk about list commas without talking about the Oxford comma, aka A Comma You Should Definitely Be Using.
Jk. Sort of. I am in favor of the Oxford comma, but I’m here to teach you about grammar, not make your decisions for you.
ANYWAY. The Oxford comma is the comma that comes before the last item in a list – in the above example, the comma before “and cracked cauldrons.” Without the Oxford comma, the example looks like this instead:
Edna devoured the sight of cursed necklaces, good luck charms and cracked cauldrons used for potion-making centuries ago.
Yep. That’s it. That’s what we’re fighting about all the time.
Why the Oxford comma? In some cases, it provides greater clarity – such as the now-infamous example of an author’s dedication to “my parents, Ayn Rand and God.” Is this a list sans Oxford comma, or is the author naming their astonishingly famous parents? Of course, in this case, it’s reasonable to assume it’s a list, but the context doesn’t always make it clear. The Oxford comma provides that clarity.
Also: the aesthetic.
Commas can also separate adjectives when multiple adjectives modify a single noun, although sometimes they’re unnecessary in this kind of list. (Not to confuse you or anything.)
The Magical Archaeology building had a face of clean, smooth, white stone.
Commas form compound sentences when joined with conjunctions.
When you’ve got a compound sentence – basically, a sentence made up of two or more smaller sentences – a conjunction should go in there alongside the comma. So instead of “it was her son’s birthday, Edna was stuck at the nursing home,” your compound sentence should look like this:
It was her son’s birthday, but Edna was stuck at the nursing home.
The coordinating conjunctions in English are and, or, nor, but, for, yet, and so. They’re a good place to start if your compound sentence has a comma but no conjunction!
Commas offset modifiers and dependent clauses.
These clauses often come at the beginning or end of the sentence and may modify all or part of the other clause of the sentence.
Unfortunately, it also had about a dozen stairs.
Here, “unfortunately” modifies – or describes – the fact that this building has stairs.
Mrs. Macready demurely claimed her prize, a motivational poster with a kitten on it.
“A motivational poster with a kitten on it” illustrates Mrs. Macready’s prize.
The wizard spoke in thunderous tones, as wizards are wont to do.
“As wizards are wont to do” describes the manner of this particular wizard’s speech as common amongst wizards in general.
This kind of comma plays a little more fast and loose than the others; depending on where the modifier or dependent clause falls, you may choose not to use a comma, especially if the modifier is a single word. For example, in the first example, if “unfortunately” came later in the sentence, I might’ve written this instead:
It also unfortunately had about a dozen stairs.
What’s the difference? In the original example, the placement of “unfortunately” suggested that it modified the entire independent clause. Placing a comma after this modifier clarifies that the modifier modifies the entire following clause. In the new example, however, “unfortunately” modifies only the verb, “had.” So by eliminating the comma and placing “unfortunately” beside “had,” where we would normally expect to find an adverb modifying a verb, we signify that “unfortunately” modifies “had” but not the entire clause.
Finally, if I put “unfortunately” after “had,” I might offset it with commas like so:
It also had, unfortunately, about a dozen stairs.
Why the commas here? With the adverb coming after the verb, the commas again clarify that “unfortunately” modifies the verb (or the entire clause) rather than the following prepositional phrase (“about a dozen stairs”).
Confused? Don’t worry! There are many ways to use commas to offset dependent clauses and modifiers. Trying sticking the clause or modifier in different places in the sentence and see where commas clarify its meaning. If you’re not sure, ask someone who’s a total dork about grammar.
(You know, like me.)
Commas offset clauses that interrupt the main thought of the sentence.
These clauses interrupt the main thought of the sentence to explain or describe something or to provide more information. (In my last example above, “unfortunately” did just this when I placed it in a new position.) They’re often little asides that could potentially be offset by parentheses or em dashes instead – but since parentheses and em dashes are so noticeable, it’s usually better to use commas, unless you want to draw more attention to the aside.
Jeanine, the activities director, was making it difficult.
Here, “the activities director” explains who Jeanine is.
Finally, with a small pop, the wizard vanished.
“With a small pop” describes how the wizard vanishes.
Basically, if you can remove this piece from the sentence without losing the main thought – “Jeanine was making it difficult”; “finally the wizard vanished” – you can probably offset the dependent clause with commas.
That said…depending on the placement of the clause, its function in the sentence, and the clarity of the sentence with or without punctuation, you may not need commas! For example, if I put “with a small pop” at the end of the last example, I wouldn’t need to offset it with commas.
The wizard vanished with a small pop.
Then again, if I retained “finally,” I might want to include a comma before “with a small pop,” because “finally” and “with a small pop” both modify the wizard’s vanishing.
The wizard finally vanished, with a small pop.
Finally, the wizard vanished, with a small pop.
Basically, I’d want a comma in that case because “finally” only modifies “vanished” or “the wizard vanished,” not “with a small pop.” Commas again add clarity!
As ever, feel free to hmu here or on Twitter with questions! Next time (hopefully sooner than I got around to this post), we’ll go over the functions of semi-colons – which, even though they scare people more than commas in general, should be less confusing!
Read the whole series on commas, semi-colons, and colons!
e.m.anderson 
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