Some of my spell checkers (including the one in vim, and the build-in one in gmail) mark the form "copiable" as an error, and insist on "copyable". This doesn't seem to make sense; the rule I always learned was that "y become i if preceded by a consonant when adding a suffix, unless the suffix starts with an i: eg "copied" or "copier", but "copying". According to this rule, the correct spelling would be "copiable", which is what I always use. But I often see "copyable", which doesn't seem right to me. (For what it's worth: Merriam Webster says that the word doesn't exist, in either form, the American Heritage Dictionary gives both forms, and the Oxford English Dictionary only gives "copiable".)

What is the correct usage, and why?

  • 2
    Uh, what is a "rule"???
    – Hot Licks
    Aug 31, 2020 at 11:51
  • Google 1grams seem to suggest that apart from brief reversals around 1850 and 1950, copyable has been the favoured (not the only correct) variant. As AHD licenses both, it's best to consider both acceptable. Choose one (perhaps the more commonly used one?) and stick with it. Aug 31, 2020 at 12:08
  • The corresponding results from the British corpus Google uses show far greater variation; copiable was in favour from 1990 to 2010, but has been pushed firmly into second place since then. Aug 31, 2020 at 12:12

1 Answer 1


The 'rule' you've learnt doesn't apply to all words. There are more "exceptions to rules" than there are "rules". For example, you can't write plaiable instead of playable.
Some other exceptions are buyable, repayable, displayable, employable, enjoyable etc.

In case of copyable/copiable, they're both used, I don't know why.

According to Google Ngram Viewer, copyable is much more prevalent: Google Ngram results for copyable/copiable

Both are correct and acceptable. Use whichever you want but be consistent.

  • 3
    Your examples all conform to the rule. The rule say when "y is preceded by a consonant". When it is preceded by a vowel, as in all of your examples, it doesn't change. Aug 31, 2020 at 13:08
  • 1
    @JamesKanze, Not sure what you mean. But compare rely-reliable with play-playable. The "rule" you're talking about is inconsistent. Aug 31, 2020 at 13:11
  • rely-reliable might be an exception, although there may also be something additional with regards to where the accent falls. I can't think of any exceptions where the -y is unaccented and preceded by a consonant. Aug 31, 2020 at 17:26
  • @James: What are you trying to say? Can you please explain with examples? Aug 31, 2020 at 17:27
  • @JamesKanze The problem that I, and apparently others here, are having is that your use of "rule". This implies an invariable result. Unfortunately, English is quite an irregular language as it has multiple origins. I will offer you “There are no rules in English, only guidance. Some guidance looks like a rule; it probably isn't."
    – Greybeard
    Aug 31, 2020 at 20:57

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