A compound modifier (also called a compound adjective, phrasal adjective, or adjectival phrase) is a compound of two or more attributive words: That is, more than one word that together modify a noun. Compound modifiers are grammatically equivalent to single-word modifiers, and can be used in combination with other modifiers. Note that in the preceding sentence, "single-word" is itself a compound modifier.
The punctuation of compound modifiers in English depends on their grammatical role. Attributive compounds—modifiers within the noun phrase—are typically hyphenated, whereas the same compounds used as predicates will typically not be (if they are temporary compounds), unless they are permanent compounds attested as dictionary headwords.
Compound adjectives, like normal adjectives, modify noun phrases. In the phrases heavy metal detector and heavy-metal detector, the latter is a compound adjective because the modifier is made of two words used in combination.
Note that not all sequences of adjectives (or other types of words) modifying a noun phrase are necessarily parts of one or more compound adjectives. Heavy metal detector and heavy-metal detector refer to subtly different things: in the first, heavy modifies metal detector, to describe a heavy device that detects metals, while in the second example, heavy modifies metal which together modify detector, to describe a device that detects heavy metals.
Hyphenation of elements
Conventionally, and with the support of modern writing guides, compound modifiers that appear before a noun phrase must include a hyphen between each word, subject to certain exceptions. Hyphens are used in this way to prevent confusion; without their use, a reader might interpret the words separately, rather than as a phrase. One or more hyphens join the relevant words into a single idea, a compound adjective.
Major style guides advise consulting a dictionary to determine whether a compound adjective should be hyphenated; compounds entered as dictionary headwords are permanent compounds, and for these, the dictionary's hyphenation should be followed even when the compound adjective follows a noun. Hyphens are unnecessary in other unambiguous, regularly used compound adjectives.
- Man-eating shark (as opposed to man eating shark, which could be interpreted as a man eating the meat of a shark)
- Wild-goose chase (as opposed to wild goose chase, which could be interpreted as a goose chase that is wild)
- Long-term contract (as opposed to long term contract, which could be interpreted as a long contract about a term)
- Zero-liability protection (as opposed to zero liability protection, which could be interpreted as there being no liability protection)
It may be appropriate to distinguish between compound modifiers whose adverb has the suffix -ly, such as quickly and badly, and those whose adverb does not, such as well. The -ly suffix on an adverb allows readers to understand its lexical category (if not in the technical sense, then at least in the sense of the intended meaning), showing that it is intended to modify the adjective that it precedes and so not requiring hyphenation. Quickly and badly are unambiguously adverbs. Other adverbs (such as well) can commonly be used as adjectives; therefore these adverbs without the -ly suffix are accompanied by a hyphen. For example, one could speak of a well-known actress or a little-known actress.
Furthermore, the word very in a compound modifier is generally not accompanied by a hyphen. Where both (or all) of the words in a compound modifier are nouns, it is seen as not necessary to hyphenate them, as misunderstanding is unlikely.
If the compound modifier that would otherwise be hyphenated is changed to a post-modifier—one which is located after the modified noun phrase—then the hyphen is conventionally not necessary: the actress is well known.
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Japanese equivalents of adjectives can compound. This is quite common for na-adjectives, which function essentially as attributive noun phrases, while it is relatively uncommon for i-adjectives, and is much less common than Japanese compound verbs. Common examples include omo-shiro-i (面白い?, interesting) "face-whitening" (noun + i-adjective) and zuru-gashiko-i (狡賢い?, sly) "crafty-clever" (i-adjective stem + i-adjective).
- VandenBos, Gary R., ed. (2010). Publication Manual of the American Psychological Association (6th ed.). American Psychological Association. section 4.13. ISBN 1-4338-0559-6.
Hyphenation. Compound words take many forms. [...] The dictionary is an excellent guide for such decisions. [...] When a compound can be found in the dictionary, its usage is established and it is known as a permanent compound.
- The Chicago Manual of Style (16th ed.). University of Chicago Press. 2010. section 7.85. ISBN 978-0-226-10420-1.
In general, Chicago prefers a spare hyphenation style: if no suitable example or analogy can be found either in this section or in the dictionary, hyphenate only if doing so will aid readability
- Merriam-Webster's Manual for Writers and Editors. Merriam Webster. 1998. p. 73. ISBN 978-0-87779-622-0.
Permanent compound adjectives are usually written as they appear in the dictionary even when they follow the noun they modify
- The Chicago Manual of Style (16th ed.). University of Chicago Press. 2010. section 7.80. ISBN 978-0-226-10420-1.
Where no ambiguity could result, as in public welfare administration or graduate student housing, hyphenation is unnecessary
- Hyphens – Punctuation Rules, GrammarBook.com
- Guardian and Observer Style Guide (see section on adverbs)
- "Spelling and Hyphenation". Northeastern University Guidelines. Northeastern University. Retrieved March 25, 2011.
- Compound Modifiers, DailyWritingTips.com
- Compound Modifiers, Writing.com
- The Chicago Manual of Style, 15th ed. 2003, Clause 5.92, p. 171
- The Associated Press Stylebook and Libel Manual, Addison-Wesley Publishing Company, Inc. (1992)