The Blue Book of Grammar and Punctuation
Dashes
Dashes can be a complex topic with many subtle uses. The various types include the en dash, em dash, 2-em dash, and 3-em dash. We will limit our discussion to the most common uses of the en and em dashes as they will fulfill the bulk of the needs of most writers.
Em dashes, like commas, semicolons, colons, ellipses, and parentheses, indicate added emphasis, an interruption, or an abrupt change of thought. Experienced writers know that these marks are not interchangeable. Note how dashes subtly change the tone of the following sentences:
Examples:
You are the friend, the only friend, who offered to help me.
You are the friend—the only friend—who offered to help me.
I pay the bills; she has all the fun.
I pay the bills—she has all the fun.
I wish you would … oh, never mind.
I wish you would—oh, never mind.
Rule 1. Words and phrases between dashes are not generally part of the subject.
Example: Joe—and his trusty mutt—was always welcome.
Rule 2. Dashes replace otherwise mandatory punctuation, such as the commas after Iowa and 2020 in the following examples:
Without dash: The man from Ames, Iowa, arrived.
With dash: The man—he was from Ames, Iowa—arrived.
Without dash: The May 1, 2020, edition of the Ames Sentinel arrived in June.
With dash: The Ames Sentinel—dated May 1, 2020—arrived in June.
Rule 3. Some writers and publishers prefer spaces around dashes.
Example: Joe — and his trusty mutt — was always welcome.
En dashes are shorter than em dashes and longer than hyphens. Like hyphens, they can be used for number ranges (see Rule 6 of Hyphens Between Words).
Examples:
The student council will meet Thursday, 3:15–3:45 p.m.
During the years 1999–2016, Joshua lived in Fargo, North Dakota.
We expect 300–325 people at the reception.
En dashes also can be used to punctuate open compound adjectives like New York based artist or Charles Dickens inspired writer. New York and Charles Dickens are called open compounds in these cases because we would not normally hyphenate them. Some writers and publishers prefer using an en dash for these situations, but a hyphen would work as well.
Examples:
New York–based artist
Charles Dickens–inspired writer
However, consider the open compound expression apple orchard scented candle. Using an en dash for this phrase may better clarify the intent for readers over using a hyphen.
Example: apple orchard–scented candle
Some methods for forming these punctuation marks on a PC:
En dash—hold down the Alt key and type 0150 on the numeric keypad
Em dash—hold down the Alt key and type 0151 on the numeric keypad
On a Mac:
En dash—press option+hyphen key
Em dash—press option+shift+hyphen key