As covered in the article ‘Use—and Non-Use—Of Dashes and Hyphens’ Part 1 and Part 2, the hyphen joins words together and is thus essential for compound words, of which there are three types:
- Open (or spaced) compounds, written as separate words (e.g. printing press, car wash or chief of staff)
- Hyphenated compounds, wherein separate words are linked with a hyphen (e.g. eye-opener, check-in, free-for-all, mass-produced or non-English-speaking)
- Closed (or solid) compounds, written as a single word (e.g. lifestyle, bookstore, birthrate or notebook)
Compound words are always in a process of evolution, towards becoming one word and then a compound noun set as two words (which is more likely if first word has two or more syllables); when a compound gains broad currency/common usage, the hyphen often falls away.
The hyphenation of compound adjectives (also known as compound modifiers) often depends on their position in a sentence/sentence structure.
Generally speaking, when preceding a noun, the hyphenation of compound adjectives lends clarity. Exceptions to this include proper nouns, and compounds formed by an adverb ending in ‘ly’ plus an adjective or participle (e.g. largely irrelevant or smartly dressed) as ambiguity is virtually impossible.
Consequently, if the two words forming the compound adjective are no longer used adjectively, they will lose their hyphen (see the examples below).
|
Adjective use |
vs. |
Non-adjective use |
| A twenty-five-year-old man. |
|
The man was twenty-five years old. |
| State-of-the-art security system. | The security system was state of the art. | |
| One-bedroom condo, with several two-, three-, and four-bedroom units available. | Our condo had one bedroom, though there were options for two, three or four bedrooms. | |
| Her fifteen-foot-long vessel. | Her vessel is fifteen feet long. | |
| A drug-resistant virus. | The virus is drug resistant. |
Conversely, a compound functioning as an adjective will commonly gain a hyphen (e.g. middle class to middle-class neighbourhood).
Remember that the main consideration of hyphen use is consistency: pick one style guide or dictionary to guide you, being cognisant of the mandated or dominant dictionary or style in your institution or geographic region. The articles on this blog, and all advice contained within them, follow the Snooks & Co. Style Manual for Authors, Editors and Printers and the Macquarie Dictionary.
