Antonym Prefixes

Form

An antonym prefix turns a word into its opposite without changing the rest of the word (happy becomes unhappy, possible becomes impossible).

Un- is the most common and the safest default with everyday words (unclear, unkind, unprofessional, unreliable). A second family of words takes in-, and within that family the spelling follows the first letter: il- before l (illegal, illegible), im- before m and p (impolite, impossible), ir- before r (irregular, irresponsible), and in- everywhere else (inaccurate, incomplete, invalid). Which family a word belongs to has to be learned word by word, because plenty of words starting with those same letters keep un- (unlikely, unpopular, unreliable). The other three prefixes each carry a meaning of their own: dis- reverses a verb or an attitude and forms a few adjectives too (disagree, dislike, dishonest), mis- means done wrongly rather than not done at all (misunderstand, miscalculate, mistranslate), and non- simply puts something outside a category (nonfiction, non-profit).

When to Use It

1. 1

   Default to un- with everyday adjectives

   His behavior at the meeting was unprofessional.

2. 2

   Change in- to il-, im- or ir- before l, m, p and r

   Parking here is illegal.

3. 3

   Learn the in- words as whole words, since similar adjectives take un- instead

   The report was inaccurate and incomplete.

4. 4

   Use dis- to reverse a verb or an attitude

   She disagreed with the committee's decision.

5. 5

   Use mis- when the action was done wrongly rather than skipped

   She misunderstood what I said and thought I was being rude.

6. 6

   Use non- to place something outside a category

   The charity is a non-profit organization.

Common Mistakes

• Un- on an in- word: write illegal or irregular, not unlegal or unregular — legal and regular belong to the in- family, which becomes il- and ir- here.
• In- before p: write impolite, not inpolite — in- becomes im- in front of p and m.
• Dis- where un- belongs: write unreliable, not disreliable — dis- reverses verbs and attitudes (disagree, dishonest), and most other adjectives take un-.
• Mis- for dis-: write I disagree with your conclusion, not I misagree with your conclusion — mis- marks a wrong action, as in misread or miscount.
• Non- as a separate word: write nonfiction or non-profit, not non fiction — non- joins the word, with or without a hyphen.