Today I’ll explain the difference between dashes, commas, and parentheses.

Have you ever been sitting at your computer writing, and suddenly you aren’t sure whether you should use parentheses, commas, or dashes to set off some extra point or an aside? It happens to me because in a lot of cases these marks are interchangeable, at least grammatically. But they each do give your writing a different feeling.

In general, you can think of parentheses, commas, and dashes as a continuum of punctuation marks. Parentheses are the quiet whisper of an aside, commas are the conversational voice of a friend walking by your desk, and dashes are the yowl of a pirate dashing into a fray.

Parentheses

Let’s start with those quiet parentheses. You use them to surround something that seems a bit out of place in the sentence — an aside, a clarification, or a commentary. Sometimes when you go back to edit your first draft, you’ll find that you can rework your sentence to include the parenthetical statement or simply delete the part in parentheses unless it’s something like an irreverent quip you’re using to intentionally set a tone.

Here’s an example of one way to use parentheses to add additional information:

The Loma Prieta earthquake (October 17, 1989) happened during a national live broadcast of the World Series, making it an especially memorable event for people who were watching. 

The date (October 17, 1989) is in parentheses in that sentence. It’s something you want to tell the reader, but it isn’t a necessary part of the sentence. If you leave it out, the reader still gets the whole point you want to make about the earthquake being a big deal to people who were watching the big game.

The date isn’t enough of a dramatic statement to merit dashes, and if you want to leave it in, another reason you might want to use parentheses is that the date already contains a comma between the day and the year, so to surround it with commas could make the sentence difficult to read. No excitement. Already has an internal comma. That leaves parentheses as the obvious choice.

Parentheses are also often a sign that you could leave the material out. I mean, if it wasn’t important enough to include in the main part, why do you need it? Is the date of the earthquake important enough to include? If so, you could rephrase the sentence to write:

The Loma Prieta earthquake happened during a national live broadcast of the World Series on October 17, 1989, making it an especially memorable event (and so on).

Here’s one that’s a little different:

I’m heading out (movie night!), but I’ll call you in the morning.

“Movie night” is more of an aside or comment than a clarification. “Movie night” is so far removed from the flow of the sentence that you wouldn’t want to use commas around it. You could use dashes. It just doesn’t seem like enough of an interruption or a dramatic statement to me to merit dashes, but that’s a judgment call. You could write the sentence a different way, of course, “I’m heading out for movie night, but I’ll call you in the morning,” but it doesn’t have the same friendly, happy feel. “Movie night!” is an informal aside, and parentheses seem like the best choice in that case.

And you may have noticed that the examples I’ve given both have sentence fragments enclosed in parentheses, but you can also enclose whole clauses.

Dashes

At the other end of the spectrum, we have dashes. If you want to hang a spotlight on your words, decorate them with dashes. You can use dashes the same way we just talked about using parentheses, to enclose fragments or whole sentences, but you’d better be sure your words are worthy of dashes. Dashes interrupt your sentence in a way that parentheses or commas don’t. Here’s an example:

They fled through the woods, and then George—dear, sweet George the accountant—jumped out from behind a tree and stabbed them.

It’s appropriate to interrupt that sentence with dashes to remind the reader that the attacker has unexpected qualities — that he’s dear, sweet George the accountant. It’s shocking!

But this is English, so there’s an exception to the dashes-are-dramatic rule. You can also consider using dashes in a more mundane sentence when the part you need to set off already has commas or is especially long.

For example you might want to use dashes to set off the list of ingredients in this sentence since the list contains commas:

Squiggly is bringing all the ingredients for s’mores — chocolate, marshmallows, and graham crackers — but not anything else we’ll need to make them.

And you might want to use dashes in this sentence because the aside is longer than the rest of the sentence:

S’mores — which get their name from smooshing together the words “some” and “more” — are Squiggly’s favorite part of camping.

Just remember that when you use dashes instead of parentheses, you’re generally highlighting the information instead of simply noting it or providing it as background information.

Dashes are the yowl of a pirate dashing into a fray.

Another difference between parentheses and dashes is that you always have to use two parentheses, they always enclose something, but it’s fine to use one dash alone to introduce an important or exciting statement, or a statement that already has commas in it. For example, you could write:

There was only one thing missing from the pirate ship — pirates.

That dash is appropriate because the announcement that the pirates are missing is probably important or dramatic. In a sentence like that, where something is defined or expanded, you’re choosing between the dash and a colon. You could just as properly write:

There was only one thing missing from the pirate ship: pirates.

That sentence just doesn’t have the same wild feeling as the sentence with the dash. A colon is a more stoic, buttoned up punctuation mark than a dash.

And as before, you can also use one dash to introduce a longer, pedestrian statement if the statement already has commas.

Commas

So let’s finish with commas. They’re kind of dull, which means you should always consider using them because punctuation usually shouldn’t be drawing attention to itself. There are a gazillion rules that govern how to use commas, so I’m going to limit this discussion to commas that could be used like parentheses or dashes.

Commas don’t interrupt your sentence, so you use them when the words you’re enclosing are a natural part of your sentence and not some flamboyant statement or comment from left field that isn’t even a grammatical part of the sentence. Commas are generally used for appositives, for example, which are defining or clarifying statements after nouns. Here’s an example of an appositive set off with commas:

Squiggly’s best friend, Aardvark, prefers fishing. 

“Aardvark” just tells you who Squiggly’s best friend is. You could set his name off with dashes as we did in the earlier sentence about George the accountant, or with parentheses like we did with the date earlier, but there’s no reason to in a sentence as short and straightforward as this one.

Commas are also often used to set off nonrestrictive elements, such as “which” clauses:

Aardvark and Squiggly agree that driving to their favorite campground, which takes about six hours, is the worst part of camping. 

Like information enclosed in parentheses, the “which” clause about the 6-hour drive could be left out of the sentence without changing the meaning. I actually did a whole episode just about “which” versus “that” and commas, so you can read if you’d like to learn more.

Summary

As I’m sure you’ve noticed by now, you could make a legitimate argument for using at least two different punctuation marks in nearly every example sentence I’ve given you, but these general rules may be helpful:

• Use parentheses when you want to enclose something that is incidental to the sentence, something that is background or almost unnecessary.
• Use dashes when you want to enclose or set off something that deserves a lot of attention, is meant to interrupt your sentence, or already has commas or parentheses in it.
• Use commas to enclose things that belong firmly in the flow of your sentence.

I know it can be frustrating that there aren’t hard-and-fast rules about when to use commas, parentheses, or dashes, but learning to use your judgment is part of finding your voice and becoming a better writer. In this case, the rules are more like the pirates’ code in “Pirates of the Caribbean” — they’re more what you’d call guidelines than actual rules. I bet Jack Sparrow never used a comma; he seems like a dash guy to me.

Parenthesis image courtesy of Shutterstock