Q: I often see a hyphen used in sentences like this: “Different animals live in fresh- and saltwater.” Is the hyphen really necessary? I think it’s ugly.
A: The short answer is that a hyphen isn’t necessary in that sentence. We’ll explain why later, but let’s first discuss what’s going on here.
To keep things simple, we’ll use another example: “He has a stomachache and a headache.”
The two nouns in that sentence are compound words, the first made up of “stomach” and “ache,” the second of “head” and “ache.” Compounds can also be hyphenated (“mayor-elect” and “governor-elect,” for example).
To get rid of an “ache” in the sentence above, the usual style is to replace it with a hyphen: “He has a stomach- and a headache.”
As The Chicago Manual of Style (16th ed.) explains it, when the second part of a compound is omitted, a hyphen is used, followed by a space. It gives this example: “both over- and underfed cats.”
Note, however, that the second part of the compound, “fed,” is the same in both words. This hyphen business doesn’t work when the second part is different.
As the Chicago Manual points out, you would write “overfed and overworked mules,” but not “overfed and -worked mules.”
We’ve simplified this a lot. If you’d like to read more about dropping parts of compounds, check out page 374 in the Chicago Manual.
Getting back to your question, why isn’t a hyphen necessary in the sentence you ask about?
Because four of the five dictionaries we checked consider the noun versions to be two words, “fresh water” and “salt water”—noun phrases, in other words.
They appear as two words, for example, in both The American Heritage Dictionary of the English Language (4th ed.) and the Oxford English Dictionary.
Merriam-Webster’s Collegiate Dictionary (11th ed.) is the lone dissenter, but we’ll let the majority rule here.
Since these two noun phrases aren’t compounds, no hyphen is needed when a word is removed: “Different animals live in fresh and salt water.”
However, the adjectives “freshwater” and “saltwater” are solid compound words in four of the five dictionaries we looked at.
So a hyphen is needed if the adjectives are used in a similar sentence and part of the first one is dropped: “The aquarium has both fresh- and saltwater fish.”
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