What's the difference between dis- and mis-, un- and non-? This negative prefix list can help you understand the important prefixes at the beginnings of words that can change a word's meaning into its opposite.
Note that sometimes one prefix is used for an adjective, and different ones are used for related nouns or verbs.
Usually, however, the same prefix serves both adjective and noun: uncertain, uncertainty; unwilling, unwillingness; unfriendly, unfriendliness, inadequate, inadequacy, disloyal, disloyalty, etc.
Examples: deactivate, decode, decomission, decompose, deconstruct, decontaminate, decrease, deflate, deform, demythologize, derail.
Note that the prefix de- in Latin (and in words that originate in Latin) has other, contrary meanings as well as sometimes making words negative. (See List of Prefixes.) It is often used as an intensifier, meaning completely (as in demand), as well as meaning from, down, or away. When used with an English verb to make a new word, it works as a negative. (Debug, defrost, devalue.)
Examples: disaffected, disability, disagree, disagreement, disagreeable, disbelief, disfigure, dishonorable, disinfect, disinherit, disintegrate, disloyal, displeased, disproportionate, distasteful, distrust.
(Tasteful refers to something that shows good taste or judgment. Things which are pleasant to the taste buds are ‘tasty.’ Distasteful refers to tasks that are unpleasant. Foods that lack flavor are tasteless. A lack of good taste in aesthetics can also be called tasteless.)
In- often changes to 'il-' before l; 'im-' before b, m, or p; and 'ir-' before r. These changes make it easier to pronounce.
Examples: illegal, illegible, illiterate, illogical, imbalance, immature, immaturity, impatient, imperfect, impossible, imprecise, inability, inaccessible, inaccurate, inadequate, inappropriate, incapable, incoherent, incompatible, incomplete, inconceivable, inconsistent, incredible, indefinite, indiscretion, inevitable, infinite, inflexible, insecure, insignificant, instability, insubordination, insufficient, invalid, invariably, invisible, involuntary, irrational, irregular, irrelevant, irreparable, irresistible, irresponsible, irreversible, etc.
Exceptions in which ‘in-‘ does not negate, but intensifies: Inflammable has the same meaning as flammable-- something that burns easily. Their opposite is nonflammable. The same is true for habitable and inhabitable (the negative is uninhabitable). Valuable and invaluable also are synonyms— except that invaluable is even stronger. It means something is priceless: so valuable that a person would not want to give it up for any amount of money.
Examples: misconduct, misdemeanor, misdiagnose (to diagnose wrongly,, misinform, misinterpret, mislead, misleading, misplace, misspell, mistake, mistaken, mistrust, misunderstand.
Note that a misdiagnosed disease is diagnosed incorrectly, as compared to an undiagnosed disease, which has not been diagnosed at all. Similarly, a misinformed person has been given wrong information, while an uninformed person simply does not know much about a subject.
Examples: nonconformist, nonentity, nonexistent, nonintervention, nonmetallic, nonpartisan, nonresident, nonrestrictive, nonsense, nonstop, etc.
Some words can be negated either with non- or with another negative. 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: unable, unacknowledged, unaffected (not affected at all; disaffected means affected badly), unafraid, unaided, unaltered, unambiguous, unanticipated, unapproachable, unassigned, unattainable, unavailable, unaware, unceasing, uncertain, unclear, unconventional, uncooperative, uncoordinated, unenforced, unexposed, unfocused, unfriendly (in this case -ly isn’t for an adverb; friendly & unfriendly are adjectives), unhelpful, uninformed, unknown, unmodified, unnatural, unpleasant, unpredictable, unprofessional, unrealistic, unrefined, unresolved, unrestricted, unscheduled, unstable, untouched, unwilling, unwise, etc.
There are other prefixes, besides the 6 on this negative prefix list, that can sometimes give a negative connotation to words. (Note 'sub-' above.) These 6 are the most common, however. They are worth knowing!
The best way to learn the different negative prefixes is to work (or play) with them. You can do both on Practice Negative Prefixes. It emphasizes academic vocabulary, so is also a good way to review about 60 common words on the Academic Word List.
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