A Way With Words: Hyphens
It seems easy enough. Hyphenate when you have two or more words linked together as a single modifier, and the linked words precede the noun they modify, and if the combination of words has a separate meaning without using a hyphen.
Remember, hyphens are used specifically to avoid confusion. The problem is that when to use a hyphen is still confusing.
Bobby is a third-grader this school year
I have an eight-year-old Labrador named Hershey
Numbers between twenty-one and ninety-nine:
two hundred and thirty-five dollars
six and three-fourths pounds
Prefixes: ex, self, all (in most instances)
When omitting the hyphen creates a new word, with a different definition:
When creating new, compound words:
When combining last names:
After Betty Jones and John Warren get married, they will change their last name to Mr. and Mrs. Jones-Warren.
When the prefix comes before a proper noun
When omitting a hyphen in a compound modifier is confusing:
A small scale manufacturing plant is coming to town. – the plant manufactures little weighing devices
A small-scale manufacturing plant is coming to town. – the plant manufactures items of limited quantity
With a list of compound words, hyphenate each prefix:
We needed to decide on four-, six- or eight-inch floor tiles.
The school chorus auditions are open to first-, second- and third-grade students.
Do not hyphenate
When the modifier is after the noun in a sentence:
Bobby is small for being in third grade.
My pet, a Labrador named Hershey, is eight years old.
When part of an accepted word:
When the preceding word is not used as a prefix:
When the meaning is clear without hyphens:
sixth century art
high school graduation,
Some of these rules can be broken, but it’s difficult to know when that is acceptable. If you’re still confused, best practice is to use a dictionary.