Pitch accent excepting, they are pronounced the same. I think it is historical. Like 大 used to be opo, but the p softened and eventually fell away altogether. I think those double vowel words tend to come from old japanese, and hence you see them in kun’yomi, whereas the おう comes from chinese-borrowed words, and hence are in on’yomi. There are exceptions, though, and they seem to be historical too. 妹 (いもうと) for example, which comes from いも (sister) + 人 (ひと) which had a vowel shift when used in that word, and became いもふと and eventually いもうと
So yeah, rule of thumb is kun’yomi has more おお, on’yomi has more おう
Seems like Mousefire already answered the question, but yeah, most of the おお sounds had an “h” sound at one point in history that later got lost. Some words can still be pronounced either way like 頬 is still widely pronounced both ほほ and ほう. I believe おおきい also used to be おほきい. I don’t think you’ll ever find a おお long vowel in an on’yomi.
The second お in a “oo” group is usually the case of a ほ or を that got changed to an お because of spelling reforms, to reflect modern pronunciation as opposed to classical orthography. I’m pretty sure only kun’yomi readings contain this kind of group.
While we’re on the topic, does anybody have any fun mnemonics or memory shortcuts for remembering which one to use? I keep getting tripped up on words like 氷 (こおり) and 十日 (とおか), and then end up hyper-correcting on words like お父さん (おとうさん) and 王子 (おうじ) and bungling them too.
Well, the first two are both kun’yomi and the second two are both on’yomi, so that rule of thumb is still holding.
But in the end, have you tried… not hyper-correcting? As I mentioned in my previous post, if you just go with ～おう as the default assumption, you’ll be correct more often than not. Then you simply need to remember the exceptions.
Ah yes, the pedagogically proven strategy of, “just like…don’t.”
I get what you’re saying, but “simply remembering the exceptions” is where I run into the issue. I go, “Was it this one that was the exception?..oop, nope, it wasn’t.”
I guess I’ll just have to make myself a jingle or something to remember.
I’m sure it’s riddled with problems (e.g. English grammar does not align with Japanese grammar, and I don’t know if 遠い can be used to refer to temporal distance, or if it can, if it can only refer to distant past, etc) but whatever, I’m frankly shocked that nothing apparently exists for this at all, considering how often the question gets asked online, and always receives the same handful of generally unhelpful answers.
“Just follow kun/on rules” is problematic for noobs like me because
a) I barely understand what on’yomi/kun’yomi even mean at this point, much less being able to apply them in any meaningful way, and
b) Yes, all おお readings appear to be kun’yomi, but not all kun’yomi readings are おお (妹 - いもうと, 弟 - おとうと, etc), which doesn’t help the problem of, “which ones are the exceptions, again?”
Hmm. You’re right, it’s supposedly intransitive, though WaniKani gives the example トンネルを通る, and jisho gives the example ヘルメットを通った and now I’m questioning my sanity and have lost all sense of what a direct object is.
I’m grateful that modern Japanese has few actual remaining kana spelling rules.
in addition to おお⇆おう (and the obvious を⇆お, へ⇆え, and は⇆わ) there is also the slightly more ill-defined case of ええ⇆えい which is generally pronounced ええ but is more likely to become pronounced えい in some cases like when someone is clearly enunciating or speaking slowly compared with the おう case.
I’ve recently also noticed song lyric transcriptions that write いく in hiragana in the lyrics even though it is clearly being pronounced as ゆく in the song.