I basically learnt that words that start with a 'm' or 'p' get 'im' as a negative prefix, whilst words starting with 'r' get 'ir' in such a case (irreverent, irrelevant).

However, I stumbled upon 'realistic'. I'm almost sure it is 'unrealistic'. A quick search on Google revealed 13 million hits for 'unrealistic'; 'irrealistic' on the contrary only results in 14.000 hits.

Therefore, is 'unrealistic' an exception to this rule?

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    The rule is bogus. You have to take the etymology into account. You would never say irready or irruly, either.
    – RegDwigнt
    Commented Mar 22, 2011 at 19:06
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    Do you say "unready"? New one to me... ;-) Commented Mar 22, 2011 at 19:10
  • 6
    Ever hear of King Æthelred (en.wikipedia.org/wiki/%C3%86thelred_the_Unready)?
    – Kelly Hess
    Commented Mar 22, 2011 at 19:12
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    @jae: you miss the point. As does Kelly, actually, as Æthelred's name has nothing to do with not being ready, and everything with being ill-advised (cf. German Rat, "counsel"). My point was that whether or not unready, unround, unright, and unrude exist, you would prefer them over irready, irround, irright, and irrude any time.
    – RegDwigнt
    Commented Mar 22, 2011 at 20:00
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    "She was young and unready for motherhood."
    – apaderno
    Commented Mar 23, 2011 at 9:22

2 Answers 2


The word realistic is negated with the prefix un-, which is not the same as in-/im-/ir-, and is not subject to the rule regarding in-/im-/ir-. The rule that you cited is correct, but only for words that take the negative prefix in-/im-/ir- (e.g. intractable, impossible, irresponsible). Words that are negated with un- always use un- (e.g. untreatable, unbearable, unready), and never vary the second letter of the prefix.

There is no general rule that will allow you to know which words take the negative prefix un- and which take the negative prefix in-.

The forms that you find on the net with the word irrealistic are either mistakes by non-native speakers, people being clever with word-play, or possibly people creating derivations off of the specialized linguistic term irrealis.

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    So, basically, "Theorem: A holds whenever A holds."? Commented Mar 22, 2011 at 19:09
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    @jae, kind of. If you know that the word is negated with one of in-/im-/ir-, then you can use the OP's rule to predict which version of the prefix to use. But if you don't know whether to negate with un- or in-, then you're pretty much hosed. Commented Mar 22, 2011 at 19:15
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    +1 — excellent answer! More examples of un + r: unreasonable, unreadable, unrelated, unrated, unrhymed
    – PLL
    Commented Mar 22, 2011 at 20:47


Never heard of such a rule. Or I may have forgotten about it. Never been a fan of rules about language anyway: you learn the rule and the myriad of exceptions (depending on rule and language in question)- Why not just learn the words, and be done with it?

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    When rules often apply, it is a good idea in my opinion to learn those instead of each single word. Of course there are exceptions, but it's useful to fall back on.
    – pimvdb
    Commented Mar 22, 2011 at 19:13
  • Yes, and why not just learn all the sentences, instead of bothering with grammar? Patterns are for the birds. Commented Mar 22, 2011 at 19:25
  • They think differently about that at my school :o)
    – pimvdb
    Commented Mar 22, 2011 at 19:48
  • I didn't learned rules (or grammer, which is rules), I just learnt the language. Just like I learn not German, I just learndit. Seriously (no, seriously seriously), I never bothered much with grammar in school (and my grades were as one would expect ;-)). We had a German-teacher who was all about comma rules; she had a catalog of rules for where to put commas, and most of the class learned those rules slavishly -- I didn't bother. I learn by... osmosis, if you will. Commented Mar 22, 2011 at 19:59
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    To put it in context: I know it's "unruly", and "not ready" and "irrelevant"... but I don't see, nor do I need, any rules behind that. So, I don't bother with them anymore. Not for the actual activity of speaking/writing. As an academic/intellectual exercise, grammar (and "rules") can be fun... but mostly by amusing oneself with the exceptions. But that's MVPO (my very personal opinion). Commented Mar 22, 2011 at 20:05

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