Grammar Smart 3rd Edition - Princeton Review 2014

J. The Hyphen
PART 4. Punctuation

A hyphen separates compound words. In etymological evolution, two words may be separate, then joined by a hyphen, then joined altogether. For instance, week end changed to week-end and then to weekend. The best way to find out about a particular word is to look it up in the dictionary.

Rules For Hyphens

1. If the pair of words forms an adjective that comes before the noun, use a hyphen.

well-known felon

first-class work

2. If the adjective pair comes after the noun, you don’t need a hyphen.

His crimes are well known.

His work is always first class.

3. Use a hyphen for fractions acting as adjectives:

He drank one and two-thirds cans of beer.

But not for fractions acting as nouns:

Two thirds of the people have gone home.

4. Use a hyphen to differentiate certain words:

He recollected his adventure in Guam.

He re-collected the money.

She recovered from the flu.

She re-covered the sofa.