Using hyphens correctly with compound adjectives seems to be a common area of confusion for many writers. As an editor I read other people’s writing every day, and I often see the incorrect use of hyphens. People often use them where they should not be used, and leave them out when they are needed.
The right place to use a hyphen between two words is in a compound modifier, which is essentially a single adjective made up of two or more words. When you use a hyphen to make a compound modifier (or compound adjective), you make it clear to readers that the words form a single adjective.
Errors of hyphenation in compound adjectives
Here are examples of the way incorrect hyphenation occurs in the types of texts I regularly see:
…the device has sufficient processing power to provide real time data analysis. [1]
…the system is able to process the data in real-time. [2]
These two examples are the complete reverse of what they should be, and it is surprising how many times I see writers making these two errors consistently throughout a text.
Example [1] is obviously unclear. Does it mean “real time data analysis” or “real time data analysis”? For those familiar with the subject and context the intent may be obvious, but there would be many cases where it would not be obvious. In example [2] the hyphen is just unnecessary.
When to use hyphens with compound adjectives and when not to
Using hyphens correctly with compound adjectives is actually easy: using a hyphen to join the adjectives in example [1] will make the meaning clear.
…the device has sufficient processing power to provide real-time data analysis. [3]
The rule is therefore:
Use a hyphen in a compound modifier/adjective when the modifier comes before the word it’s modifying.
Or more generally: if a compound adjective can be misread, use a hyphen.
Using the hyphen when it follows the word it is modifying (example [2]) is unnecessary.
Other places to use hyphens correctly
Hyphens are also often needed in adjectives between a prefix and the base word, to make it more readable or to remove ambiguity.
Words that may be ambiguous
- The Bluetooth devices may need to re-pair. [pair again, not repair]
- When it cools the original shape will re-form. [form again, not reform]
Words where the prefix ends and the base word begins with the same vowel
- co-operation
- anti-intellectual
Generally most words formed of prefixes and suffixes do not use a hyphen. This is another place I often see unnecessary hyphens (eg: multiphase, not multi-phase).
Words beginning with self
- She was suffering from low self-esteem.
- The site provides self-paced training.
Special cases
- Captalised: He has to appeal to the pro-Christian members of the party.
- Abbreviation: The test would be part of ongoing pre-HSC assessment.
- A number: The words can be said to have changed post-911.
- Multiple words: The system offers many plug-and-play features.