After commas, dashes and hyphens are perhaps the most common cause of punctuation confusion I see.
Hyphens (-) are not to be confused with either the en dash (–) or the em dash (—) (there’s another post for that) So what are they and how are they different?
A hyphen is the shortest dash-like punctuation, and the only one you’ll find on your keyboard. A hyphen is used to connect two or more words or pieces of words into one word. Sometimes, using a hyphen can slightly alter the meaning of the words it connects into one meaning. Hyphens are a lot less common than they used to be, but you still use them in three main ways:
Hyphens can be used to join two (or more) pieces of a word that has been separated, usually at the end of a line. This is less common than it used to be, as it serves little purpose in digital media. However, you will still see it in print, especially newspaper, where space is at a premium. If you are using hyphens like this, make sure the placement of the hyphen doesn’t mislead the reader.
Take the word serves above. If I had to separate it, I would use ser-ves. If I wrote se-rves or serv-es, the reader would be thrown off. Similarly, if you separated helmet as he-lmet instead of hel-met, readers would have a much harder time understanding the word.
Additionally, hyphens are used when listing compound words. For example:
Does the period go in- or outside of quotation marks?
Knowing your punctuation can improve your writing two-, three-, or fourfold!
Another use for hyphens is creating compound words. There are numerous different kinds of compound words based on which parts of speech the words are that make them up and which parts of speech they become as a compound, but I’m not going to get into the nitty-gritty details here.
Some examples of compound words made with hyphens:
He viewed the world with child-like wonder.
She wore noise-cancelling headphones on the plane.
Meeting her future mother-in-law for the first time was nerve-wracking.
Two of the above examples are correct as written, but the hyphen is not required. The following examples:
He viewed the world with childlike wonder.
She wore noise cancelling headphones on the plane.
are just as correct as the previous versions.
So how do you know when to use it? This use for hyphens might be the most complex, but if you remember that your goal is to communicate effectively, then it becomes simpler. Just ask yourself if including a hyphen in compound makes your meaning clearer or looks better. You probably don’t need a hyphen in noise cancelling headphones because it is obvious that cancelling refers to noise rather than headphones, but you should never leave them out of mother-in-law.
Another way to remember is to decide whether the hyphenated version is used so frequently (and for so long) it has become its own word, with its own separate meaning. Noise and cancelling are two words that you combined to describe the headphones, but they are not inexorably linked in our language like mother-in-law is.
In a similar trend to mother-in-law, childlike has become its own word, but here, the hyphen has been phased out completely.
When in doubt, consult your favorite dictionary. And whatever you decide, remain consistent. As with all grammar, if you make a reasonable choice and stick with it, it’s right.
Hyphens are also used to attach prefixes to stem words. However, this use is also increasingly fading. Prefixes (such as co-, un-, uni-, de-, pre-, post-, etc.) were once frequently used with hyphens, but over the last few decades their use has diminished significantly (you’ll notice the word prefix will never need a hyphen).
When would you put a hyphen in a word including a prefix?
You should always use one between pre- and a name or date.
The building was built pre-1900’s.
The dress was pre-Victorian in style.
It’s more common when the stem of the word begins with a vowel and the prefix ends with a vowel (i.e. co-own), but many words have evolved to exclude the hyphen even so (i.e. preempt, cooperate).
The cats believe they co-own my dog.
He refuses to cooperate with them.
Your best solution here again is to consult your dictionary (the same one, please) and be consistent.
Remember, the function of punctuation is not to trip up the writer, but rather to make reading easier. Any punctuation used effectively will be invisible to the reader, while punctuation used improperly or inconsistently will draw a reader’s attention to the mechanics of your writing, rather than the substance.