How to tell apart U and O sounds

I know Japanese better orally than I do written, so that may be behind my problem, but I have a lot of trouble remembering whether a long sound is written out in hiragana as お or う. (Sounds that would be written “–” in katakana.) So I can never seem to remember if 氷 is こおり or こうり, if 十日 is とおか or とうか, or if 八日 is ようか or よおか. There doesn’t seem to be any rhyme or reason to it. Any ideas to help me?

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I have the same problem, as far as I know there isn’t even a difference in pronunciation…

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Best advice I have is that it’s almost always う and you should learn the お ones as exceptions. (Perhaps include the fact that it’s お in your mnemonics.)

Edit: Having thought about it, all the examples with お I can think of are kun’yomi. 炎, 滞る, etc. So they’re complete words that originated in Japanese, rather than on’yomi parts of compounds that originated in Chinese.

(Note that する verbs are more likely to be on’yomi, since they’re really noun + する rather than independent words.)


おう is the standard spelling for the long o sound – back in the day, words with the long o sound being seen as おお/oo today like 大きい (おおきい) and 氷 (こおり) used to actually have an “oho” sound (i.e. おほきい/ohokii and こほり/kohori) but has since faded away to just a long o overtime, which is why we see おお sometimes in modern Japanese.

Thus, you’ll only see おお in kun’yomi readings and おう in on’yomi readings :slightly_smiling_face:


That’s super helpful and fascinating – thank you!

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That’s a great hint, thank you!

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