When two words come together to create a single new idea that expresses meaning different from that of either of the individual words, the result is a compound word.
Sometimes compound words include hyphens (not to be confused with em dashes or en dashes, which we also discuss on this site).
The Three Types of Compound Words
- Open compounds are written as separate words, such as “school bus” and “high school.”
- Hyphenated compounds, such as “merry-go-round” and “well-being,” are the second type.
- Closed compounds are those written as single words, with no hyphenation. Examples include “flowerpot” and “redhead.”
Function Affects Treatment
Compounds can function as different parts of speech. In such cases, the type of compound can change, too.
“Carry over,” for example, is an opened compound as a verb but a closed compound (“carryover”) as a noun or adjective:
- The money from that line item will carry over to next year’s budget. [verb form]
- The money used for the trip was part of the carryover from last year’s budget. [noun form]
- Carryover funds can be used to cover a deficit. [adjective form]
Determining When We Need Hyphens
Not sure about the part of speech? First try looking up the compound in a dictionary. Some compounds are hyphenated regardless of their function in a sentence.
For example, “on-site” is a hyphenated compound as an adjective or as an adverb, and so is the noun “right-of-way”:
- The team conducted on-site visits. [adjective form]
- The team conducted its review on-site. [adverb form]
- Drivers must yield the right-of-way to pedestrians at crosswalks. [noun form]
Not All Compound Words Are in the Dictionary
When the compound is not in the dictionary because it’s being formed for a very specific situation, we rely on guidelines provided by the style manual to which we adhere. Our style manual of choice, the Chicago Manual of Style, has a lengthy section devoted to compound words, evidence that the rules are not simple.
Unfortunately, on this issue even the fairly straightforward rules about hyphens leave some room for a writer’s own judgment.
The Texas Law Review Manual of Style says this about creating a compound word: “When two or more words are combined to form a modifier immediately preceding a noun, join the words by hyphens if doing so will significantly aid the reader in recognizing the compound adjective” (20).
The “if” clause in that sentence is the tricky part.
The Goal: To Avoid Ambiguity
One way to decide if a hyphen is necessary is to see if the phrase might be ambiguous without it.
For example, “large-print paper” might be unclear written as “large print paper” because the reader might combine “print” and “paper” as a single idea rather than combining “large” and “print.”
Another such example is “English-language learners.” Without the hyphen, a reader might think we are talking about English people who are learning any language (“English language-learners”) rather than people who are learners of the English language.
On the other hand, few (if any) native speakers would be confused by the phrase “chocolate chip cookies” or “Saturday morning cartoons.” In other words, the open compounds “chocolate chip” and “Saturday morning” are so well known that there is no room for ambiguity.
The open compound “high school” is so common, for another example, that we would not hyphenate the phrase “high school students.” We would, however, likely hyphenate “high-risk” in the phrase “high-risk students.”
Hyphens and Past Participles: Position Matters
We also use hyphenation to join a word to a past participle, creating a single adjective: “a well-intentioned plan,” for example, or “a horseshoe-shaped bar.”
Be aware, however, that we do not hyphenate these same phrases when they FOLLOW the nouns they modify:
- This is a government-mandated program.
- The program is government mandated.
- She is a well-respected student.
- She is well respected as a teacher.
No Hyphens with “-ly” Adverbs
We never hyphenate compounds created with “-ly” adverbs, even when they PRECEDE the nouns they modify: “a fully developed plan,” for example, or “a nationally certified teacher.” Here are more examples:
- We sent in heavily fortified troops.
- The troops were heavily fortified.
- All newly employed nurses must be evaluated regularly.
- All the nurses on the eighth floor are newly employed.
- A beautifully designed room can be both relaxing and invigorating.
- The living room is beautifully designed.
(See also our article about hyphenating adjectives preceding nouns.)
Two important points:
- We have three types of compounds: open compounds, closed compounds, and hyphenated compounds.
- Many of them are found in the dictionary and are not subject to interpretation, judgment, or whim. Start with your dictionary before applying any other guidelines. (On-line dictionaries are easy to use. We favor Merriam-Webster’s New Collegiate Dictionary, and the American Heritage Dictionary.)
Can you spot any errors in the use of compounds in the following sentences?
- The situation in the Middle East continues to be a closely-monitored media event.
- The Department of Transportation maintains rights-of-way alongside all roadways.
- Follow up activities have been scheduled for June and July.
- We must follow up on these changes.
- Long term planning must be an essential goal of this company.
- The committee centers all of its recommendations in performance based standards.
- The situation in the Middle East continues to be a closely monitored media event. [No hyphen with an “-ly” adverb, even though here it helps form a compound adjective preceding a noun.]
- correct [Webster’s hyphenates “right-of-way” and the plural form “rights-of-way” in all circumstances, even when the phrase is functioning as a noun, as in this sentence.]
- Follow-up activities have been scheduled for June and July.
- Long-term planning must be an essential goal of this company.
- The committee centers all of its recommendations in performance-based standards.
©2018 Get It Write. Revised 2019.