Avoiding Punctuation 'Mass Hysteria' Hyphens and dashes have different uses. They cannot be used interchangeably.

My favorite exchange from the 1984 movie "Ghostbusters" comes when the team is trying to convince the mayor of New York to let them out of jail so they can re-capture the ghosts running amok in the city.

Dr. Peter Venkman: This city is headed for a disaster or biblical proportions...
Dr. Egon Spengler: Forty years of darkness! Earthquakes, volcanoes..
Winston Zeddemore: The dead rising from the grave!
Dr. Peter Venkman: Human sacrifice! Dogs and cats living together! Mass hysteria!

I sometimes like to apply those lines of dialogue to punctuation: "Hyphens and dashes being used the wrong way! Mass hysteria!"

Hyphens and dashes have different uses. They cannot be used interchangeably. Though the incorrect use of these punctuation marks may not cause mass hysteria, it's still important to get it right.

Here's how to tell the difference and use each correctly.

Hyphens

Hyphens connect words, prefixes, and suffixes, and are generally used to avoid ambiguity. For a complete discussion of these hyphenation rules, please see the article "Heading off hyphenation headaches."

Hyphens are also used to separate numbers that are not inclusive, such as telephone numbers or social security numbers. Hyphens are likewise used in URLs, email addresses, and to spell out a word letter by each letter.

800-888-8888
hyphen-dash.com
heinous is spelled h-e-i-n-o-u-s

Em dashes

Em dashes can be used when you want to introduce additional information in a sentence, but don't want to set it off with commas or parentheses:

My piano teacher—an exceptionally patient woman—was visibly agitated by my ham-fisted playing.

Em dashes can also be used to separate a pronoun from what it refers to:

Sam is the perfect gentleman—articulate, charming, and handsome.

Em dashes can also be used to convey a more emphatic aside:

Your brother—no matter what he says—cannot make you unconscious just by looking at you.

En dashes

En dashes are longer than a hyphen, but half the length of the em dash. En dashes connect continuing numbers, such as dates, times, and pages. They can also be used to indicate an unfinished number range.

Please read chapters 2–12 tonight.
The party is from 7–9 p.m. Saturday.
The vote was 125–127 against the resolution.
Philip Pullman (1946–)

Double em dashes

The double em dash is used to indicate missing letters in a word, either because the material is missing, illegible, or to conceal a name.

The patient and Dr. S—— agreed to settle the case.

Triple em dashes

The triple em dash is used to indicate missing words.

I admire ——— too much to expose him in this article.

Hysteria aside, dashes and hyphens convey particular meanings. As the Chicago Manual of Style states, "Though many readers may not notice the difference—especially between an en dash and a hyphen—correct use of different types is a sign of editorial precision and care."