I’m convinced that one of the most troublesome pieces of punctuation for people (wow…that was some alliteration!) is when, where, and why to hyphenate. When I first started proofreading for publishers, I think this one area gave me fits more than any other. And, just when I think I had a hyphenation rule figured out, I’d learn an exception to that rule!
So, I’ve put together a short list to hopefully help alleviate you of some of the frustration I faced. These are some basic guidelines, but be aware that exceptions do exist. And, while dictionaries are good for confirming whether or not a word or phrase should be hyphenated, they won’t help you when it comes to general principles. For that I would suggest consulting some form of style manual (Chicago Manual of Style or the AP Manual of Style, for example).
1. Think in terms of clarity. If a word could possibly be misread if left unhyphenated, then it should have a hyphen. One example is coop (as in chicken) vs. co-op. Many terms over the years have morphed from hyphenated to closed, such as web-site, which is now almost always written as website. One reason for this change in publishing is because it takes up less space. I realize that one hyphen doesn’t account for much space by itself, but over the course of a magazine article or book, they can. And space is money if it’s not online (that word also used to be hyphenated, by the way).
2. Sometimes used with prefixes. For the most part, nearly all prefixes are written without hyphenating, but there are some exceptions. The word self is always hyphenated before another word (except in the case of selfless); the prefixes pre or post are typically not hyphenated unless they are used before a proper noun (pre-Civil War era or post-World War II); the prefix co will be hyphenated only to avoid confusion in reading. Most other prefixes are written as closed, but be sure to check in the dictionary to be certain you’re not dealing with an exception.
3. Use with compound modifiers before a noun. This rule probably trips writers up more than any other when it comes to hyphenation. So, if you have a phrase with an adjective and a noun (open + space, for instance), and put that phrase before another noun, it would become hyphenated: open-space park. Likewise, if you have an adverb that does not end in ly combined with an adjective (well + known), it would also become hyphenated before a noun: well-known actor.
But … (you knew that was coming, right?), adverbs that do end in ly never get hyphenated (highly paid actor). I don’t believe there are exceptions to this rule. This hyphenation rule only applies when the modifiers appear before the noun. So, you would say “well-known actor” but “the actor was well known.”
4. Use with adjectives or adverbs when combined with participles before a noun. Similar to the above rule, you would say “open-ended question” (adjective and participle) but “the question was open ended.” And, you would say “much-needed attention” (adverb and participle), but “the attention was much needed.”
5. Use when part of a hyphenated term is omitted. In an expression such as: “I can’t decide whether to go with the twenty- or thirty-year mortgage,” twenty keeps the hyphen because it still forms a compound with year mortgage.
6. Use with fractions. Fractions will always be hyphenated whether they appear as nouns, adjectives, or adverbs.
7. Use with compound adjectives or adjectival phrases before a noun. This would include the forms of ordinal numbers, colors, and age terms. Examples include: First-floor window, three-year-old dog, black-and-white dress, over-the-counter drug. Remember that these same phrases will not be hyphenated if used after the noun.
OK, well I think that’s probably enough hyphenation rules for one day! Believe me when I say, however, there are many more. Again, be sure to check a dictionary for specific examples, but be aware you may not find everyone you need. And, spell checker will definitely not catch these for you. If this is an area you struggle with, I would highly suggest investing in a good style guide, which will have every possible rule along with its exception. This is one of the most-worn sections (notice the hyphenation there!) of my style guide, to be sure!