Negative Prefixes

Most of us grow up learning the negative prefixes by hearing them spoken in context. But, what determines which prefix to use in order to form that word’s opposite? Why is it unlawful, but it’s illegal? Why is it infirm, but it’s impaired?

And how do you know what prefix to use when you need to invent a word with a negative prefix? There’s actually are some rules. Some negative prefixes are used depending on the language derivation and meaning, and some are used depending on what letter follows.

Here are some guidelines for how to use these common parts of speech.

The most common negative prefixes in English are a-, anti-, de-, dis-, il-, im-, in-, ir-, non-, and un-. While some of these prefixes are interchangeable in some uses, there are subtle differences between them. Following are some examples of each:

a- and an-

These prefixes are derived from Greek, and mean “not” or “an absence of something”. A- is added to words that start with a consonant, and an- is added to words that start with a vowel. They’re typically added to adjectives ending in -al. Exception: Words that start with ‘h’—depending on the root word, either prefix may be (e.g., ahistorical, anhydrous).

Examples: apolitical, asexual, asymmetrical, atheist, atypical.

Exceptions: Not all words that appear to have a negative prefix are negative. Example: alike.


This prefix from Greek then Latin means “against”, “opposite”, “in opposition to”, “defense”, or “prevention”.

Examples: antidepressant, anti-inflammatory, antimissile, antisocial, antithetical, antivirus.


This prefix is usually added to verbs to denote reversal of an action.

This prefix in Latin (and in words that originate in Latin) has other, contrary meanings and sometimes makes words negative. It’s often used as an intensifier, meaning “completely” (as in demand), and may mean “from”, “down”, or “away”. When used with a verb to make a new word, it works as a negative.

Examples: deactivate, debug, declassify, decode, decompose, deconstruct, decontaminate, decrease, deflate, deform, defrost, demythologize, derail, devalue.


This Latin prefix has several meanings: “absence or lack”, “not; opposite of”, or “removal; reversal of an action”. Words with dis– as a negative prefix may begin with a vowel or a consonant.

Examples: disabled, disaffected, disagree, disapprove, discomfort, disconnect, disenfranchise, dishonest, dishonorable, disloyal, dismount, disorient, distasteful.

Exceptions: Not all words that appear to have a negative prefix are negative. Example: discuss.


This prefix means “bad or difficult”.

Examples: dysfunctional, dyslexic.

in-, il-, im-, ir-

These are derived from Latin, and mean “not; the opposite of; lack of a given quality””. The last three of these are variations of in-. They’re used to create a better sound: il- is used before ‘l’; im- is used before ‘b’, ‘m’, or ‘p’; and ir- is used before ‘r’). These prefixes are generally the least useful of the negative prefixes, because they only go with certain Latin-derived stems (e.g., impenetrable, inarticulate, intolerant).

Words with il– as a negative prefix begin with the letter ‘l’. Examples: illegal, illegible, illiterate, illogical. Exceptions: Not all words that start with “i” have il- as a negative prefix (e.g., unlicensed).

Words with im– as a negative prefix begin with the letter ‘m’ or ‘p’ (only example for ‘b’ is imbalance). Examples: immaterial, immature, immaturity, immeasurable, immobile, immoral, immovable, impartial, impatient, imperfect, impolite, impossible, improper. Exceptions: Not all adjectives that start with an “m” or “p” have im- as a negative prefix (e.g., unmistakable, unpopular, unimportant).

In- is the second most common negative prefix. Words with in– as a negative prefix may begin with either a vowel (except ‘I’ or ‘u’) or a consonant. Examples: inability, inaccessible, inaccurate, inadequate, inappropriate, incomplete, incorrect, indecent, independent, ineffective, inefficient, ineligible, inevitable, informal, inorganic, insane, instability.

Words with ir– as a negative prefix begin with the letter ‘r’. Examples: irrational, irreconcilable, irregular, irrelevant, irreparable, irresistible, irresponsible, irreversible.

Exceptions: There are cases where in- does not negate the stem word, but instead, it intensifies it. So, for example, inflammable has the same meaning as flammable. Other examples include habitable and inhabitable, radiate (“emit rays, spread out”) and irradiate (“expose to radiation”), and valuable and invaluable (invaluable is stronger, meaning “priceless”).

Exceptions: Not all words that appear to have a negative prefix are negative. Examples: illuminate, important, incline, indulge, insist, and invoke, involve, irrigate.

Rare prefix: -ig, which is used before ‘n’ (e.g., ignoble).


This prefix means “wrongly”.

Examples: misconduct, misdiagnose, misfire, misguide, misinform, mislead, misleading, misplace, misspell, mistake, mistaken, mistrust, misunderstand.


The Latin prefix non- (“not”) is the most useful negative prefix—it can be attached to almost any noun, verb, adjective, or adverb. Non- is generally used to create a word that’s the complete opposite of its positive form. When non- is added to a word, no hyphen is required, unless the stem is a proper noun. A spell-checker might catch an unhyphenated non- word you may create, but this doesn’t mean that your invented word is wrong. Words with non– as a negative prefix may begin with a vowel or a consonant.

Some words can be negated with either non- or with another negative prefix. In those cases, non- has a more neutral connotation. For example, nonstandard means “not according to the usual standard”, but substandard is “below the standard: not good”. Nonreligious means “not religious”, but irreligious means “more actively opposed to religion”.

Examples: nonconformist, nonentity, nonessential, nonexistent, nonfiction, nonmetallic, nonpartisan, nonprofit, nonresident, nonsense, nonsmoker, nonstop, nontoxic.


This Latin prefix means “not; the opposite of; lack or absence of; reversal”. Un- is the most common negative prefix, and is usually attached to words derived from Latin that end in suffixes such as -ed and -able, and create adjectives. Words with un– as a negative prefix may begin with a vowel or a consonant.

Examples: unable, unaffected, unafraid, unassailable, unbelievable, uncertain, unclear, uncoiled, uncomfortable, unconcern, unemployed, unexpected, unfair, unforgettable, unfortunate, unfounded, unfriendly, unhappy, unhelpful, unimportant, uninformed, uninteresting, unkind, unknown, unnatural, unopened, unrealistic, unfriendly, unpleasant, unprepared, unstable, untouched, unusual, unwilling, unwise.

Exceptions: Not all words that appear to have a negative prefix are negative. Example: universe.

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