A prefix is a small word element that is attached to a following word, for example in sub-Saharan and submarine, where sub- means ‘below’ or ‘under’. A hyphen is used with some prefixes in some cases.
The table below lists a number of prefixes common in university and research writing:
| Prefix | Without Hyphen | With Hyphen |
| anti | antibiotic | anti-American |
| co | cooperative | co-operative |
| intra | intravenous | intra-arterial |
| micro | microbiology | micro-organism |
| neo | neoclassical | neo-Nazism |
| non | nonconformist | non-nuclear |
| post | postwar | post-Keynesian |
| pre | prerequisite | Pre-Raphaelite |
| pro | proceed | pro-American |
| re | reform | re-form |
| self | selfish | self-absorbed |
| semi | semicircle | semi-independent |
| sub | submarine | sub-Saharan |
Most prefixes do not normally use a hyphen; however, they may do so in the cases discussed below.
When to use a hyphen with a prefix
To make a word easier to read
A hyphen can be used to make a word easier to read:
Where the prefix and root have the same letter
meta-analysis
pre-emptive
re-entry
anti-inflammatory
non-nuclear
co-occur
cross-sectional
But
override
overrated
underrated
underrepresented
To avoid a confusing combination of letters
anti-apartheid
Before a capital letter
non-Hodgkin’s lymphoma
pan-African
post-Keynesian
Pre-Raphaelite
Proto-Indo-European
sub-Saharan
With an abbreviation
non-SI
pro-EU
anti-US
With a date
pre-1900
post-1945
To avoid ambiguity
to reform the United Nations
to re-form the United Nations
With self-
Most compounds with self- are written with a hyphen:
self-adhesive
self-confidence
self-rule
But
selfish
selfless
non-
Non is somewhat of an exception, as both forms with and without a hyphen are found:
| Without Hyphen | With Hyphen |
| nonessential | non-essential |
| nonfiction | non-fiction |
| nonproliferation | non-proliferation |
US English tends to use non without a hyphen (apart from cases such as non-nuclear where the following word begins with n). In British English, both styles are used.
In your text, you should decide whether to use non with or without a hyphen, following the style of your target publication or a single dictionary as your guide.
Note: your word processor may not distinguish systematically between non spellings with and without a hyphen.