Hyphens in fractions?

May 14, 2010 4:48 PM

When writing fractions as words, under what circumstances do you hyphenate them?

I'm always confused about hyphenating fractions. Is it "one-and-a-half" or "one and a half"? Do you only use hyphens only when the fraction modifies a following noun, or are the fractions always hyphenated regardless?

And what about times? "Half-past seven" or "half past seven"?

posted by stenoboy to writing & language (6 answers total)

Depends on the style manual, but generally, if you're using it as an adjective, hyphenate. So:

Half-past seven (yes)
One-and-a-half cookies (yes)
One-half cup (yes)

It's not actually wrong the other way, just clearer this way. But if you need to know for a particular discipline, check the style manual. IIRC, AP says no to hyphens, Chicago Manual of Style says yes.
posted by eleanna at 4:55 PM on May 14, 2010

Er. Addendum. You do not hyphenate when a fraction is being used as a noun:

So..

They ate half a pizza.
Two halves make a whole.

You also do not hyphenate if the fraction is complicated enough to already have hyphens:

He felt sick after eating sixty-six hundredths of the pizza.

Or when the fraction comes AFTER the noun:

The pizza was divided into thirds.
posted by eleanna at 5:01 PM on May 14, 2010

Copyeditor here, basically agreeing with eleanna. Different strokes for different style manuals, but routinely hyphenating the fractions (not the noun following: one-half, but a half hour) will keep you out of trouble unless you're specifically expected to use (say) AP.

BUT:

Half-past seven (yes)

No! It's "half past seven," "a quarter past seven," etc. There is no fraction "half-past." It's parallel to "an hour after takeoff"; "half" is short for "a half hour."
posted by languagehat at 5:02 PM on May 14, 2010 [5 favorites]

Exactly. Use a hyphen when you're literally writing out a distinct numerator and denominator:

One and one-third, but;
One and a third.

Half past seven, but;
One-half past seven.
posted by tepidmonkey at 6:41 PM on May 14, 2010

You will basically never go wrong just by omitting hyphens entirely when it comes to fractions. They are sometimes optional but it is hard for me to think of a scenario in which they are required.

I certainly prefer "one and one third" and "one half past seven" to the hyphenated alternatives. "One third" literally means that, a single third. There is no need to throw in a hyphen.
posted by dfan at 7:29 PM on May 14, 2010

> You will basically never go wrong just by omitting hyphens entirely when it comes to fractions.

That would be the case if you were King of the World. But since you're not, your preferences are pretty much irrelevant for anyone but you. You can, in fact, go badly wrong "just by omitting hyphens" if you're working with anyone using some of the most common style manuals.
posted by languagehat at 4:57 PM on May 15, 2010 [1 favorite]