How to Use an Em Dash

The em dash is a punctuation mark that can add style and clarity to your writing when used precisely and sparingly.

What is it?

The em dash is a versatile and striking punctuation mark that is written as a horizontal line: —.

It’s longer than its siblings in the dash family, the hyphen (-) and the en dash (–), and written lower on the page than the minus sign (−).

An easy way to distinguish the em dash from the en dash is that the em dash is as wide as the letter M, and the en dash is as wide as the letter N.

How is it used?

The em dash is a versatile “jack of all trades” that can be substituted for commas, parentheses, colons, and semi-colons.

1) Em dashes can add supplementary information and commentary, like commas and parentheses, especially if the sentence is already comma-heavy.

“Three scientists — Wilkins, Watson, and Crick — jointly received the Nobel Prize.”

2) Em dashes can introduce lists, like colons, especially where the writer wants to draw attention to the elements of the list.

“DNA is composed of four nucleotides — adenine, cytosine, guanine, and thymine.”

3) Em dashes can connect clauses, like colons and semi-colons, especially when one of the clauses amplifies or contradicts the other.

“DNA is found in nearly all living cells — but its structure was not discovered until the 1950s.”

The key distinction is that an em dash also adds emphasis.

How do you use it in academic writing?

Consider the paragraph below.

“An em dash is versatile — but it should be used infrequently. Em dashes can replace other punctuation marks — colons, semi-colons, parentheses, and commas. Try not to use em dashes — which can really slow down the reader — too frequently and close together.”
Too many em dashes are distracting, even when they’re used correctly. Em dashes make readers pause, so em dash overuse makes writing feel choppy and discordant.

As a broad guideline, try to avoid using em dashes in subsequent sentences and in more than one or two sentences per paragraph.

In an academic context, try also to avoid using em dashes to set off information that is subjective. Consider the examples below:

“This previous finding by our research group — representing a breakthrough in this research area — paved the way for this study.”

“The discovery of the structure of DNA — marking the beginning of modern molecular biology — was an outstanding achievement.

These two sentences are both grammatically correct, but depending on the context, the reader might feel that the em dash in the first example draws unnecessary attention. In the second sentence, the em dash feels appropriate to the historical significance of the finding.

Because it’s rarely absolutely necessary to use an em dash, em dash usage is considered a matter of stylistic preference. Em dashes can be informal or distracting in an academic context, and some academic writing style guides advise scientists to avoid em dashes altogether.

However, em dashes can also effectively vary the rhythm of your writing, highlight important information, and clarify complex sentences when used with purpose. We recommend using em dashes selectively and infrequently to highlight key information.