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")

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
(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 / recover
(If there were no hyphen in "re-cover," it could be confused with "recover," meaning "return to a normal state.")
• re-press / repress
(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.
(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:

Prefix	Meaning	Example
a-, an-	without	amoral, atypical
ante-	before	antecedent, antenatal
anti-	against	anti-establishment
auto-	self	autopilot
circum-	around	circumvent
co-	with	co-conspirator, co-pilot
com-, con-	with	companion, contact
contra-	against	contradiction
de-	off	delist, devalue
dis-	not	disappear
en-	put into	enclose, envelop
ex-	out of, former	extract, ex-governor
extra-	beyond, more than	extracurricular
hetero-	different	heterosexual
homo-	same	homonym, homophone
hyper-	over, more	hyperactive
il-, im-, in-, ir-	not, without	illegal, impractical, inconsiderate, irresponsible
in-	into	insert
inter-	between	internet, intersection,
intra-	between	intranet, intravenous
macro-	large	macronutrients
micro-	small	microscope
mono-	one	monocle
non-	not, without	nonentity, nonstarter,
omni-	all, every	omnipresent, omniscient
post-	after	post-mortem
pre-, pro-	before, forward	precede, project
sub-	under	submarine, substandard
syn-	same time	synchronize
super-	above	supervisor, superhuman
trans-	across	transmit
tri-	three	tripod, triceratops
un-	not	undone, unfinished,
uni-	one	unicorn, unilaterally

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