Proofreading is not just about checking spelling, punctuation and grammar. It’s about checking for sense, consistency, spacing, coherence to style guides and more. A spell-checker alone is just not enough … and this can be explained with a poem:
These similar-looking marks can show up in your marketing copy. If you’re wondering how they’re used and how they’re supposed to be formatted, here’s a brief explanation of the most common uses:*
This little bit of line is used to join words or words with prefixes/suffixes. There should be no space on either side of it. The rules of hyphenation can be complex and controversial. Editors hyphenate differently from other editors. Style guides differ. Associated Press (AP) style has a more general approach than “The Chicago Manual of Style” (Chicago style). Examples: co-worker, paraben-free, small-business woman, blue-green water, high-quality care, e-commerce
En dash –
An en dash is longer than a hyphen. In Chicago style, it is used for ranges of things such as years, ages, months, numbers, etc. There should be no space on either side of it. In AP style, a hyphen is used in ranges. Examples: 2001–2003, July–December, pages 3–45, Wednesday–Saturday
In running text, it is best to use words instead of an en dash (or hyphen in AP style). For example, from 2001 to 2003. Don’t mix words with the en dash: from 2001–2003.
Em dash —
The em dash is an even longer line. It is used to interrupt a sentence or to emphasize a phrase. There should be no space on either side of it. In AP style, there is no such thing as an em dash. Instead, AP style uses the en dash for this use, and puts one space before and after it. Example: Begin the new year—your best one yet—with positive, fresh energy.
In marketing and advertising, AP style is the preferred style, along with a house style guide that may include a preference for the Chicago style usage of all three marks, -, – and —, instead of just the two in AP style.
This chart gives a quick rundown:
*There are other places where these marks are used (the hyphens in phone numbers, for example) and the marks can be combined. There’s even a 2-em dash and a 3-em dash in Chicago style.