Are there any patterns to observe in choosing the correct negative prefix to use, as in unbelievable, disproportionate, asymmetric, and intolerable? (There are other negative prefixes as well, but these are the ones I usually mix up.)

Un- and in- are probably the ones I most frequently mix up, as in *untolerable/intolerable, *unedible/inedible, *unexact/inexact, *unappropriate/inappropriate, ... I realize these are all in-, but why? Is there anything to look for there?


4 Answers 4


Agreeing with the answer Shinto Sherlock gave from Fowler, World Wide Words says,

In general, words take un- when they are of English (Germanic) origin and in- if they come from Latin. (The forms im-, il-, and ir- are variations on in-.) Apart from that, there’s really no good guide to which one you should choose.

Following the link will give you an expanded discussion of this topic.

  • wasn't a- also for Latin / French derived words?
    – Abel
    Commented Sep 5, 2010 at 11:57
  • Hi Daniel, u mentioned about a link in your last statement. Where is the link?
    – Part Timer
    Commented Aug 28, 2012 at 8:29
  • @PartTimer the link is above the quote or here is the url: worldwidewords.org/qa/qa-unv1.htm.
    – Daniel
    Commented Aug 28, 2012 at 12:32

a- and an- are used in words with Greek origin, (meaning no, absence of, without, lack of, not in said language). Other Greek prefixes are ana-, (meaning again, up, on, above, c.f. anabaptist literally meaning "re-baptist") and anti- (meaning against, c.f. antidemocrat).

Anyway, the thing is that as language is a living thing with lots and lots of users (especially in the case of English, where there also are a lot of different cultures, further contributing to the confusion), and therefore, rules like this tend to be mixed up (especially when creating new words or combining already existing ones). The rule of thumb is that, as previously stated:

  • un- is used in words of Germanic origin,

  • in- in words of Latin origin (and generally in words from other Latin-derived languages, like Spanish or French),

  • a- and an- is used in words of Greek origin.

Prefixes like de-, dis- and dys- come from Latin or Greek and have a slightly different meaning.

Note that un-, in- and a-/an- have the same origin, but they have taken very different ways into our language of today.

  • -dys is obviously not from Latin. Here's a hint: the Latin name for Y is I Graeca - the Greek I.
    – Angelos
    Commented Jul 27, 2016 at 19:28
  • There are exceptions, especially in more recent words: amoral (Greek a + Latin) was coined to be distinct from immoral. Similarly, asexual.
    – DjinTonic
    Commented Nov 4, 2023 at 13:44
  • There are exceptions, especially in more recent words: amoral (Greek a + Latin) was coined to be distinct from immoral. Similarly, asexual. Also unattractive and undaunting are non-Germanic.
    – DjinTonic
    Commented Nov 4, 2023 at 13:51

Fowler says:

The general principle that un- is English and belongs to English words, and in- is Latin and belongs to Latin words, does not take us far.

There is a lot more which you can read in Google books.


The general rule is to choose the prefix according to the etymology of the word:

However, the un- prefix is usually used for Latin derivatives that end in suffixes such as -ed and -able , resulting in adjectives such as unfounded, unassailable, and unbelievable. This to prevent confusion with another Latin prefix with identical appearance but a different meaning of "to cause to", which appears in words like illuminate, irradiate, or inflame.

Latin-derived words with un-:

  • unattractive
  • unconscious
  • undaunting
  • unfortunate
  • unimportant
  • unpleasant
  • unpopular
  • unprepared
  • unproductive

Roots with different prefixes for adjective and noun forms:

  • unstable and instability
  • uncivil and incivility
  • unable and inability

Roots with both un- and in- variants with distinct connotations:

  • inhuman and unhuman
  • indigestible and undigestible
  • inconsolable and unconsolable
  • inartistic and unartistic


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