Premise

You’ve probably seen em dashes in one form or another. They appear everywhere from fancy published research journals to fringe conspiracy theory blogs in the deepest corners of the Internet. But what are they really? And more importantly: how and why do they work?

Quite simply, em dashes are longer dashes that add—or insert—additional points of information and or commentary into your writing. Note that information added within or onto sentences can technically either be full sentences themselves or incomplete sentences, but the latter is most often the case for em dashes—since semicolons are only used to connect thematic commentary via linking more closely two grammatically complete sentences, which you can review here.

Examples

Let’s take a look at a couple of sample sentences where em dashes might elicit an interesting effect. Here are some examples where they add commentary onto the end of a sentence:

• “I voted for the senator because I decided that he would be the better of the two options—a decision that I’m sad to say that most other New Yorkers didn’t make.”
  • Effect: the part added after the em dash in an additional point of commentary. Connecting it to the original sentence via the em dash identifies an unfortunate situation here according to the writer. I.e. it’s particularly sad that other New Yorkers didn’t also come to the same decision—an idea that is expressed more dramatically by not outright explaining it with redundant reiteration of the main idea.

Let’s look at another example of this type, but one that instead clarifying emphasis to the original idea:

• “The mood in the bunker was that of fear—fear about not knowing what was really outside.”
  • Effect: it explains what this “fear” was, which almost works like using a colon to prompt an answer. But since we already identified what we were talking about before the em dash, we would use that instead.

And finally, let’s take a gander at an em dash that inserts new information within a sentence:

• “The company—headed, again, by Dr. Mundale—told her that the leave request was denied.”
  • Effect: the inserted information here clarifies who we’re talking about, but also something that their’ doing (i.e. “heading” some sort of effort). The reason why you would use em dashes here and not parentheses (like I’m doing here right now) is to emphasize that this additional, clarifying information is particularly noteworthy, important, or dramatic.

So why use em dashes, and not, say, parentheses? Well, em dashes literally add more visual space between the additional information and the rest of the sentence. Pauses are inherently more dramatic….don’t you think? Just consider which of these two examples seems more dramatic to you:

• “The president (the same man who drone bombed children) had been considering a nuclear strike according to the report.”
• “The president—the same man who drone bombed children—had been considering a nuclear strike according to the report.”

Again, parentheses work better for more formal, clarifying information (which is actually the reason why in citation styles, they used to identify sources). Save the em dashes to really highlight your ideas—and the quality of your writing!

Alternative Usage

Sometimes you see em dashes used as parts of lists like this:

— cookies

— bread

— milk

This isn’t necessarily right or wrong to do—although typically, you’ll see lists with bullet points or hyphens instead. Again, these are genre conventions that may vary from one written type of documentation to the other, so keep this context in mind when you see em dashes and other such formatting used out in the wild.

Further Considerations

• Note that em dashes are actually different from “hyphens” and “en dashes.” Yes, you read that right, folks. There are actually two other dash forms, as mentioned here. The difference:
  • Hyphens are the shortest, often used to combine words into compound ones. E.g. “well-meaning.”
  • En dashes are often used between dates. E.g. “2009–2014.”
  • You might not even notice the difference between these two variants, but it does exist. The reasons are subtle, but important.
• Often, students mis-format em dashes, as per the examples above. Why is this important? Just consider how this sentence might confuse a reader:
  • “I was never thought of as well -meaning because I broke the rules.”
    • Does this sentence mean, “They never thought I was a good person because I broke the rules?” Or is it stating that, “They didn’t think that I was well. This was because I broke the rules?” This is why you want to make sure you get your dashes right!
• It’s often difficult to not overuse em dashes once you get the hang—and effect—of them! So think of these as like other forms of advanced punctuation! You wouldn’t want to use exclamantion marks at the end of every sentence—like we’re doing in this bulleted example here! Doing so can make the meaning feel dull from overuse. Instead, consider targeted areas to get the most bang for your em dash!