Emphasizing Information in Writing: Parentheses, Commas, & Em-dashes

Here are three ways to add non-essential information to a sentence:

• Parentheses: Most people (myself included) don't sleep enough. [de-emphasis]
• Commas: Most people, myself included, don't sleep enough.
• Em-dash: Most people—myself included—don't sleep enough. [emphasis]

Note: The grammar term for this extra information is an appositive. Appositives generally go in the middle or end of the sentence (rarely at the beginning).

Parenthesis, Commas, and Em-dash: Details & Examples

To de-emphasize (not highlight) the extra information, use parentheses.

• Bring a change of clothes (if you want) for the party.
• John patted Lily (his dog) on her back.
• It happened the year she was born (1998).  

In regular (neutral) cases when you don't feel a need to deemphasize or emphasize an idea, use commas.

• My brother, a doctor, is not able to work from home.
• The book mentioned the city of Niagara Falls, on the US-Canada border.
• Canberra, the capital, is the sixth most populated city in Australia.

Sometimes you want to emphasize the extra information. Though it's not grammatically necessary in the sentence, it may be important. In these cases, use an em-dash, which is also called a parenthetical dash.

• The book—published in 2001—does not discuss social media.
• The man beside me—whom I'd never met—asked to use my phone.
• The cause of the accident—this is the key point—was equipment failure.
• I'd like to thank our team—especially the part-time staff.

I was shocked by what the child was watching—a horror film!

Notes on the Em-dash:

• An em-dash is longer than a hyphen. (It is called an 'em' dash because its typesetting has the same width as the letter 'M').
• Do not put a space before or after an em-dash.
• Using em-dashes is somewhat trendy nowadays. Avoid using them too often in your writing.

Using an Em-dash instead of a Colon

It is possible to use an em dash instead of a colon (our lesson on colon use is here).

• He was absent for the usual reason—he had completely forgotten about it.
• My stomach was thinking about something else—chocolate.

When introducing a list, use a colon when the list is at the end of the sentence, but an em-dash when the list begins a sentence.

• You'll need three things: a swimsuit, a hat, and a towel. (list at the end)
• A swimsuit, a hat, and a towel—that's what you'll need. (list at the beginning)

Writing an Em-dash in a Word Processor (e.g. Microsoft Word)

At the end of a word, type two hyphens in a row, and then begin the next word. Do not add any spaces before or after. When you finish writing the second word, the two hyphens will turn into an em-dash.

Clarification: Em-dash or Hyphen?

We use a hyphen (-) for these purposes:

1. to make a compound word (a word made of two or more smaller words). Examples: son-in-law, log-in screen, user-generated.
2. to break a word into two parts so it can fit on a line. The hyphen is always put between syllables.
3. to connect two surnames, particularly for married couples who each want to keep both names. E.g. Lisa Johnson-Smith

I hope this lesson on punctuation has been helpful. Please leave your comments or questions below.

— Matthew Barton / Creator of Englishcurrent.com

References

• Em Dash. (n.d.) The Punctuation Guide. https://www.thepunctuationguide.com/em-dash.htmlEngkent, L. (2013).
• Skill Set with Grammar. (2nd ed.). Oxford Press.
• Guffey, M., Seefer, C. & Burke, P. (2013) Canadian Business English. (6th ed.). Nelson Education.

Related

• When to Use Commas in Adjective Clauses