A prefix refers to a group of letters placed in front of a (base) word, which ends up changing the meaning of the word. Common prefixes include pre-, pro-, dis-, de-. On their own, prefixes have specific meanings. For example, dis- means “opposite.”

Prefixes can indicate position, show repetition, or make a word negative. Some of the most common prefixes that make words negative include un-, in-, and dis-. For example, adding the prefix un- to the word successful creates the word unsuccessful, which means not successful. Another common prefix is re- that indicates repetition. For instance, adding re- to the word construct creates the word reconstruct (to construct again). Common prefixes that can indicate position include sub- (means below or under) and supra- (means above). For example, sub is found in common words like submarine and subway.

There’re several rules that students need to consider when adding a prefix to a word. When adding a prefix, they shouldn’t change the spelling of the prefix or the original word. For example, the words unhappy (a combination un- and happy), undo, and disappear all demonstrate this guideline. Students should follow this rule even if the spelling leads to double consonants, such as in the words cooperation and misspell.

Students need to be careful to notice the prefix look-alikes. Some words comprise the same string of letters of a prefix, but they aren’t prefixes. For example, the re in real isn’t a prefix.

There’re several cases where students need to use a hyphen with prefixes. A hyphen needs to be used when adding a prefix to a numeral or a proper noun (e.g., pre-1990 and un-American). Students need to use a hyphen when adding the prefix ex only when it means former (e.g., ex-president). If ex means away from or out of, the use of a hyphen will lead to misreading (e.g., in expel). Hyphens also help to prevent confusion with other words. For example, students need to hyphenate re-cover (to cover again) to prevent confusing it with recover (to repair or regain). A hyphen should always be used after the prefix self- (as in self-respect). Students should hyphenate to separate two “I”s, two “A”s, or other letter combinations that may cause mispronunciation or misreading (e.g., anti-intellectual, ultra-ambitious, and co-worker). They may also use a hyphen to separate two “O’s or two “E”s to prevent mispronunciation or improve readability (e.g., co-opt vs. coordinate and de-emphasize vs. reenter).