When did Old Slavic ЪI become Ы?

  • 1
    While the question is a bit terse and doesn't show evidence of research, I don't necessarily see the reason for the downvotes.
    – jogloran
    Commented Apr 2, 2021 at 22:59
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    @jogloran Not showing evidence of research is the canonical reason for downvoting. There's no good reason for the close votes, though.
    – Cairnarvon
    Commented Apr 3, 2021 at 0:52
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    @Cairnarvon In terms of not demonstrating evidence of research, I don't see this question as being any worse than (e.g.) linguistics.stackexchange.com/questions/38682/…, which has 23 upvotes and counting. The only difference is the terseness, which is not a rules violation.
    – jogloran
    Commented Apr 3, 2021 at 1:18

1 Answer 1


The question would be better asked as “When did the OCS ЪИ become ЪІ and when did ЪІ become Ы?” The three variants were originally used interchangeably, but later Ы took over, the most obvious reasons being it had the simplest shape of the three and since the yers disappeared as sounds it became irrelevant which one to use, ЪІ or Ы.

The first dated Cyrillic printed book Octoechos, 1491, in Kraków, by Schweipolt Fiol, had the letter as Ы, and since then all the printed Cyrillic books followed that trend. You can see lots of Ыs in this spread from the Octoechos, the first one is about the middle of the top line of the left page:

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So the answer to your question is: by the end of the 15th century AD Ы became the only one.

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