I am a beginner in Japanese and I've noticed that when two words are compounded into one word the first letter of the second word changes.

hira + kana = hiragana

ko + hayashi = kobayashi

ori + kami = origami

This pattern would imply that the word Katakana should be Katagana.

Any ideas as to why this is ?

NB. I am not referring to Kanji having different readings in Japanese. That is a different issue. I am specifically referring to compound words where the first letter of the second word undergoes a change.

2 Answers 2


This phenomenon is called 連濁 (rendaku). The basic rules for rendaku can be found in the following question, so please take a look at it first:

Now, in addition to the rules mentioned in the linked question, there is yet another rule (or "tendency") regarding rendaku: there are several kanji that tend to block rendaku for whatever reasons.

According to Mark Irwin, a prefix 片- (かた; meaning "part", "fragment") is one of such kanji, and many words that start with 片 somehow block rendaku. See this presentation (PDF) for details.

  • 片言 かたこと
  • 片恋 かたこい
  • 片時 かたとき
  • 片仮名 かたかな

Likewise, 御【お】-, 御【ご】-, 一【ひと】-, 二【ふた】-, 唐【から】- and so on tend not to accept rendaku:

  • 御酒 おさけ
  • 一葉 ひとは
  • 唐傘 からかさ

Some kanji including -姫【ひめ】, -先【さき】, -浜【はま】 block rendaku when it's the second component of a compound:

  • 砂浜 すなはま
  • 歌姫 うたひめ

Unfortunately, even researchers do not know why these kanji block rendaku. It may be worth remembering which kanji tends to block rendaku, but please keep in mind that there are many exceptions like 二葉(ふたば). Ultimately, you have to remember each word individually.

  • 1
    But, for 片 you still say かたがわ (片側) so also for 片 there seem to be exceptions.
    – Tuomo
    Commented Jul 16, 2019 at 13:42
  • 7
    @Tuomo 側 is inherently voiced even without rendaku (e.g., 彼の側【がわ】に立つ).
    – naruto
    Commented Jul 16, 2019 at 13:46
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    Yes, I fixed my comment for the 姫路 part, sorry for reading your post badly. I guess you are probably also right about the 側 (although I wonder why I get it as one of the options when typing in かわ on my keyboard and searching for the kanjis)
    – Tuomo
    Commented Jul 16, 2019 at 13:50
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    @Tuomo In modern Japanese, the kun-reading of 側 is almost always がわ, but it used to be read also as かわ. We still say こちらっ側 (こちらっかわ), etc.
    – naruto
    Commented Jul 16, 2019 at 13:54
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    Thanks! I tried to see if I similarly get a 号 and 合 as options when typing in こう instead of ごう but that didn't seem to work. I can't come up with any place where 側 would be pronounces as かわ but I believe you
    – Tuomo
    Commented Jul 16, 2019 at 13:57

Unfortunately I think there is no logical explanation.

Even a pair of 2 identical kanjis may have "both versions" eg when used in names.

One example is 大島 ("big island"), with the "大島" that island being southwest of Tokyo, close to Izu peninsula is "shima", there is a railway station in Tokyo with the same kanji, but that one is "jima"

  • 2
    Maybe so. In words where the kanji is changing its reading totally (like for 小原 comparing おばら and こばら I certainly agree with you. But, what comes to adding or not the ゛I thought my example was related (as for the above mentioned 小原 comparing こはら and こばら)
    – Tuomo
    Commented Jul 16, 2019 at 13:36
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    I disagree that this is a different phenomenon. "Ooshima" and "Oojima" may be place names, but they are still effectively compound words in the same way that "hiragana" and "katakana" are compound words.
    – David
    Commented Jul 16, 2019 at 23:20
  • @David After further thought I agree with you.
    – Kantura
    Commented Jul 18, 2019 at 13:29
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    @Tuomo Actually Tuomo your example is valid. I was distracted by the Kanji. It seems that Oojima follows the Rendaku pattern while Ooshima does not. So Ooshima is in the same boat as Katakana, they both resist Rendaku. And as you suggested, there may be no logical explanation. Just an exception.
    – Kantura
    Commented Jul 18, 2019 at 13:33
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    Sorry for mixing in the kanjis. The thing was, how to highlight that the two pronounciations were written in the same way. Before posting I was actually first trying to [reverse-]engineer a theory about the ゛being used whenever it makes it easier from the pronounciation point of view, and realized that (eg due to 大島) my theory was doomed ;-(
    – Tuomo
    Commented Jul 18, 2019 at 13:46

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