Hyphens in Prefixes

Should I put a hyphen after a prefix?

A prefix is a half word (e.g., anti-, ex-, post-, pre-) placed before a word to modify its meaning. Most prefixed words can be written with or without a hyphen after the prefix.

General Guideline with Prefixes

As a general guideline, avoid the hyphen if you can, but if the unhyphenated version is a spelling mistake (let your spellchecker do its job) or looks too unwieldy for you, use a hyphen.

Here are some fixed rules:
  • Always use a hyphen with "ex-" and "self-,"
  • Never allow ambiguity (e.g., write "re-press the shirt" not "repress the shirt")
hyphens in prefixes
Read more about prefixes.

More Guidance with Hyphens in Prefixes

There is often confusion over whether a hyphen should be used with a prefix. In other words, should you write "re-consider" or "reconsider," or "anti-aircraft" or "antiaircraft"?

Unfortunately, there is no simple rule governing this, but here are some guiding principles.

Guiding Principles for Hyphens with Prefixes

If it's not a spelling mistake to avoid the hyphen and you can bear how the word looks without it, then avoid the hyphen.

Often, it's your choice whether to use a hyphen. Lots of prefixed words can be written with or without a hyphen. Here is the guiding principle:

Guiding Principle

Avoid a hyphen with a prefix. However, if you feel the word looks too unwieldy without a hyphen or if your spellchecker highlights it as wrong, use a hyphen.

Applying the Principle

Here are some examples to explain the guiding principle:
  • antiaircraft
  • ("Antiaircraft" is not wrong, but it looks a little unwieldy. If you feel the same way, write "anti-aircraft.")
The following words are all correct with or without a hyphen. However, remember that the guiding principle is avoid the hyphen if you can.
  • proactive
  • prehistoric
  • ultraviolet

Detailed Guidance on Hyphens with Prefixes

Use a Hyphen with a Proper Noun

If your prefix sits before a proper noun, use a hyphen. For example:
  • un-British
  • pro-Nazi

Do Not Allow the Same Vowel to Double Up

If the prefix ends in the same vowel that the root words starts with, separate them with a hyphen. For example:
  • semi-industrious
  • re-enter
  • ultra-argumentative
However, particularly when the vowel is an "o," if you can bear how the word looks without a hyphen and your spellchecker lets it through, then omit the hyphen. For example:
  • coordinate
  • cooperate
  • coowner wrong cross
  • (Your spellchecker (or dictionary) will not let you have "coowner.")

You Can Let Different Vowels Double Up

When a prefix ends in a vowel and the root word starts with a different vowel, omit the hyphen. For example:
  • proactive
  • reactivate
  • semiautonomous
  • (However, if your spellchecker doesn't like it or you cannot bear how it looks, go for a hyphen. For many, " semiautonomous" looks too unwieldy.)

Use a Hyphen with "Ex" and "Self"

The prefixes "ex" and "self" are followed by a hyphen. For example:
  • ex-husband
  • self-aware

Eliminate Ambiguity Every Time

If the unhyphenated version could be confused with a different word, add the hyphen. (This is most common with the prefix "re." For example:
  • re-cover correct tick / recover wrong cross
  • (If there were no hyphen in "re-cover," it could be confused with "recover," meaning "return to a normal state.")
  • re-press correct tick / repress wrong cross
  • (If there were no hyphen in "re-press,"Could be confused with "repress," meaning "subdue with force.")

Enjoy the Leniency

Most prefixed words exist in both forms. As you might have noticed in the guidelines above, it is often down to how the writer feels about the word.
  • The attack would take place at night as the anti-government troops did not possess infrared goggles. correct tick
  • (In this example, the writer did not like the look of "antigovernment" or "infra-red," so chose the versions above. That's fine. Readability – as the writer sees it – trumps all guidelines.)

Some Common Prefixes

Here are some common prefixes:
a-, an-withoutamoral, atypical
ante-beforeantecedent, antenatal
co-withco-conspirator, co-pilot
com-, con-withcompanion, contact
de-offdelist, devalue
en-put intoenclose, envelop
ex-out of, formerextract, ex-governor
extra-beyond, more thanextracurricular
homo-samehomonym, homophone
hyper-over, morehyperactive
il-, im-, in-, ir-not, withoutillegal, impractical, inconsiderate, irresponsible
inter-betweeninternet, intersection,
intra-betweenintranet, intravenous
non-not, withoutnonentity, nonstarter,
omni-all, everyomnipresent, omniscient
pre-, pro-before, forwardprecede, project
sub-undersubmarine, substandard
syn-same timesynchronize
super-abovesupervisor, superhuman
tri-threetripod, triceratops
un-notundone, unfinished,
uni-oneunicorn, unilaterally
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This page was written by Craig Shrives.