I am currently studying Japanese grammar through Japanistry's Grammar Guide (https://www.japanistry.com/the-number-system/)

I've come across a section when it says that a reading changes when two kanji join. For example, the Tsu (つ) character may be used and sometimes a dakuten (or handakuten) is added.

Yes, there's a chart but it's really confusing for me.

Is there a name for this process? Yes, I know it's almost irrelevant to on and kun readings but what is this called? Is there any more resources I can research that might help me? I want to know more about this. Thank you.

4 Answers 4


There's a page here on the 9 different changes that can occur in Japanese when words or syllables are joined. https://jn1et.com/hennonngennshou/

The insertion of a つ is 促音化 sokuonka (gemination in English).

The general rules are relatively straightforward for most two on-yomi compounds.

  1. First character reading ends in tsu followed by k, s or t -> tsu changes to sokuon (発射 hatsu+sha = hassha)
  2. First character reading ends in ku followed by k -> ku changes to sokuon (国歌 koku + ka = kokka)
  3. First character reading ends in tsu followed by h -> tsu changes to sokuon, h changes to p (出版 shutsu + han = shuppan)
  4. First character reading ends in n followed by h -> h changes to p (新品 shin+hin= shinpin)

In words of three or more characters, the gemination can be optional for the third character. It is more likely if the three characters are thought of as one word, rather than as word+suffix. E.g. sentaku (washing) + ki (machine) -> both sentakki and sentakuki are allowed

Rendaku, which is specifically the voicing of consonants in compounds, is not common for on-yomic compounds, but can happen. E.g. 融通 is yuuzuu, which has rendaku changing the reading of 通 tsuu to zuu.

Kun-yomi, numbers and some other compounds can be less regular, although there are general rules. And there are, as always, exceptions to the above.

  • Thank you. This really seems really helpful, I believe the number system follows it as well. Commented Sep 28, 2018 at 21:32
  • Yes, I know the small Tsu character is a pause but it being added is rather interesting. Thank you so much. Very much! <3 Commented Sep 28, 2018 at 21:41
  • Numbers don't always follow it. E.g. 3分 => さんぷん but 3本 => さんぼん, not さんぽん; yon almost never changes the following syllable (4分 => よんぷん is colloquially common, よんふん is standard; 四日 よっか is the only standard change I can think of); hachi sometimes geminates, sometimes doesn't; ichi, roku and juu geminate almost without exception before s,k,t and h, despite not ending in tsu. Commented Oct 1, 2018 at 9:06
  • @brownsardineThis is a total aside, but do you happen to know what font the Japanese on that site you linked is? It's perfect !! jn1et.com/hennonngennshou
    – kandyman
    Commented Nov 9, 2018 at 23:05
  • nevermind, I found it. It's Yu Gothic. Very nice looking font, first time I saw it.
    – kandyman
    Commented Nov 9, 2018 at 23:08

I believe the name for this process is rendaku.

More here: https://en.wikipedia.org/wiki/Rendaku


You're describing what's known as sandhi, specifically rendaku and gemination. It happens a bunch in Japanese, but the rules are notoriously complex. For example it's unclear to me why 学祭{がくさい} couldn't be がっさい.

You can read about it some more here.

  • Thank you very much! It's really interesting, this Rendaku or れんだく in Hiragana. What is the process called when adding or bridging つ? Commented Sep 28, 2018 at 10:21
  • @SteveWoods It's called gemination.
    – Ringil
    Commented Sep 28, 2018 at 14:05
  • I noticed く becomes っ usually only when it's followed by another k sound. I might be wrong though, never paid that much attention to it
    – Ordoshsen
    Commented Sep 28, 2018 at 15:00

It is called 音便 (onbin).

But this is not something that beginners should worry about.
Instead of trying to guess the pronunciation of words, you should just consult the dictionary.

For example 学校 is listed in the dictionary:
So you can see that 学校 is pronounced がっこう.

There are many words out there whose pronunciations (and meanings) can be quite unexpected, so it is not a good idea to try to guess.
It is much better and simpler to just consult the dictionary.

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