I would like to know what the difference is between the two spellings of the long o (ō), in hiragana, namely おう (ou) and おお (oo). Are these pronounced the same?

If so, then why does Japanese have these two different spellings for the same long o vowel?

Also, when transcribing from a textbook that uses romaji to teach Japanese, and entering the characters at the keyboard, is there a set criterion for curbing which combination I should be using (and dots it matter)?



1 Answer 1


According to the wikipedia page, the difference is due to historical reasons.



Words that were originally written with を or ほ are now written with お.
Example: おおきい (大きい)

All other words are now written with う
Example: こうしん (更新)

  • You haven't answered whether the is the same (long o), our whether a diphthong pronunciation (consisting of two vowels is also possible, as :/ the Chinese 口 (kou))? Thanks. Commented Oct 12, 2016 at 14:59
  • 1
    I am not sure about the pronunciation. I think it is the same, but I have heard people saying O-o-sa-ka, for example.
    – hisao m
    Commented Oct 12, 2016 at 15:02

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