Hyphens, En-dashes and Em-dashes

Hyphens, en-dashes and em-dashes are frequently used punctuation marks that are just as frequently misunderstood. All three marks are essentially horizontal lines, though their lengths vary. However, these three different marks have very different purposes, and using a hyphen to do an m-dash’s job is just as much of a punctuation error as using a question mark in place of a comma.

A hyphen is the shortest in length of the three. It is used to divide words that break at the end of a line, or to connect parts of compound words such as go-between, ill-fated and run-of-the-mill. The hyphen is easily found on the keyboard to the right of the zero. There is no space before or after the hyphen.

The en-dash, which is shorter than an em-dash and longer than a hyphen, is used to indicate a range of values, such as a span of time or numerical quantities (similar to using the words “to” and “from”); for example, 9 AM – 5 PM, Monday – Friday or ages 5 – 8. Most often, a space is placed before and after the en-dash, however page ranges in bibliographies and indexes usually do not contain spaces (Research in Post-Compulsory Education, 13(2), 217–226.)

An em-dash is the longest of the three, and is used to indicate a break in thought—as illustrated in this sentence. It can also be used to separate a thought within a sentence—such as this one—which would then require an em-dash at the beginning and the end of the phrase. Em-dashes generally do not have a space before or after.

You should never use two hyphens in place of an em- or en-dash. This typographically incorrect practice is a holdover from typewriter days, when there were no dashes on the keyboard at all, just hyphens. Now there’s no excuse for this very un-dashing and unprofessional habit.

In MS Word, the em dash (—)is normally created automatically when two hyphens are typed (with no space before or after). It can also be created by entering CTR+ALT+hyphen (on the keypad).
The en dash (–) is normally created automatically when two hyphens are typed (with a space before and after). It can also be created by entering CTR+hyphen (on the keypad).