I was going to add a tag for issues of my GitHub repository, to describe an issue that would not be able to be reproduced.

Here are the four versions of this word I can think of:

  • Irreproducible
  • Unreproducible
  • Non-reproducible
  • Not Reproducible

What are the difference between these words? Are they all correct? And which one is better for a tag name?

Also, is there any rule to pick the prefix for these negative forms of the word?

I know you can say 'irrational' but not '*unrational', 'unlikely' not '*non-likely', and 'impossible' not '*unpossible'. But I don't know how to pick the correct one for other adjectives. Is there a rule or pattern for this?

(Asterisk marks illicit/ill-formed words.)

  • 7
    I think it would be more accurate to use something like ‘Couldn't reproduce’ instead.  Because in practice you haven't proved that an issue can't be reproduced; you've merely tried and failed.  What if someone later finds a way to reproduce it?
    – gidds
    Commented May 14, 2021 at 12:43
  • 1
    If you want to write correct, simple, and easy-to-understand English, always use "not". Not reproducible, not likely, not possible, etc. FWIW (native British English speaker) I can see what "irreproducible" means, but I would never say or write it.
    – alephzero
    Commented May 14, 2021 at 13:03
  • A one-off issue. But I just don't think any of these is right for this context.
    – Lambie
    Commented May 14, 2021 at 14:33
  • 6
    The standard IT phrase to reject such issues is "Can't reproduce", or a bit more formal "Cannot reproduce"., so I'd choose one of these. From the spellings you suggest, irreproducible is the most common, as elaborated below by Void, and as witnessed by the famous Journal of Irreproducible Results. But 'irreproducible' is a much stronger statement than 'cannot reproduce'. Commented May 14, 2021 at 14:47
  • 1
    I think there's a subtle difference in meaning when you label something un- or ir- reproducible, as opposed to "not reproducible." The prefixed words to me suggest an intrinsic quality, while the two-word phrase describes a specific circumstance or situation. "We did not reproduce x" is not as definite as "x is irreproducible." But that may be attaching meaning where there really isn't any.
    – user8356
    Commented May 14, 2021 at 17:29

2 Answers 2


There isn't a hard-and-fast rule to determine which negating prefix to use; however, there's a very loose ‘guideline’1 that sometimes works:

  • un- is usually prepended (attached) to Germanic words
  • in- (or il-, im-, ir-)2 is usually, although not necessarily, prepended to Latin words

Reproducible is derived from reproduce which is in turn derived from Latin rēprōducō, so the negative adjective should logically be irreproducible, though that doesn't mean unreproducible doesn't exist.

Even though the root word is Latin, it can take the Germanic prefix un-. (English is a very flexible language.) Both irreproducible and unreproducible coexist and mean pretty much the same thing, but according to Google Ngram, irreproducible is more prevalent than unreproducible and non-reproducible.

All the options you list are equally correct and you can use whichever you prefer, although I'd say not reproducible rolls off the tongue quite nicely (personal opinion!). But if you need a single word for the tag, you can use both irreproducible and unreproducible interchangeably.


1. World Wide Words

2. all those are the assimilated forms of in-

  • Thanks you so much! I thought there can only be one.
    – Hao Wu
    Commented May 14, 2021 at 10:04
  • 1
    In this case for some reason I find irreproducible quite hard to pronounce so I too would prefer not reproducible.
    – mdewey
    Commented May 14, 2021 at 12:30
  • @mdewey - You would change the first e from long vowel to short vowel. Try it. It's much more pronounceable. The vowel shift will occur for that very reason. There is probably some rule that defines this but it's beyond me.
    – EllieK
    Commented May 14, 2021 at 13:02
  • @EllieK Well, yes, "irrepressable" is a probably more common word that "unrepressable" ("repress" has a short e) but mispronouncing a word by changing a vowel doesn't make your speech easier to understand.
    – alephzero
    Commented May 14, 2021 at 13:08
  • @alephzero - I find both pronunciations when I search the word. Oddly, the dictionary entry either provides one or the other but never both. Is it a British pronunciation? I have no idea what point you are trying to make with the word irrepressible but don't let that stop you. Were you thinking irreparable?
    – EllieK
    Commented May 14, 2021 at 14:11

Unreproducible or not reproducible. Note the corrected spelling.

  • 3
    'Irreproducible' is also attested and equally correct.
    – Void
    Commented May 14, 2021 at 6:23
  • 1
    Correct, but I think unlikely in context. Commented May 14, 2021 at 7:56

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