Between using the prefixes non-, ir-, i-, and dis-, a-, or un-, meaning "not (root word) to do something", when is the best time to use each?

  • Consult a dictionary. Or do you mean: how should you invent your own words?
    – GEdgar
    Dec 20, 2014 at 21:13
  • @GEdgar -- well, I'm not trying to invent a word, but a particular word I looked up had multiple prefixes, ended with the same meaning.
    – Trevor
    Dec 20, 2014 at 21:18

1 Answer 1


You use each prefix with the words that can take that prefix. I'm sorry, but that is the whole of the answer.

There are tendencies which might help (for example, in- and its variants il- and ir- are only used with words of Latin origin, a- with words of Greek origin, and un- mostly with words of Germanic origin. But even if you know the origins of words, these rules are not reliable.

  • Germans seem to experience particular difficulty in choosing the right ones. I had a colleague whom I swear used to toss a coin, and would talk about things being unpossible, and inofficial. In other respects he would speak faultless English.
    – WS2
    Dec 20, 2014 at 21:39

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