I've spent some time solving Fakepapershelfmaker NACLO problem, and later at solution I've read that some japanese letters do not require replacement while compounding.

In Japanese you should replace letters in the atomic words to give the compound word a specific meaning (for instance, initial h with b, initial k with g, and so on). As I've understood, this is a trick in order to exclude ambiguity.

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However, solution says that some letters do not require a replacement. I guess that it could lead to ambiguity of compound words. And my question is: do Japanese really has such letters? And, if yes, in which way the ambiguity in this case is excluded?

  • 1
    This question would fit better on the Japanese SE. Commented Nov 11, 2016 at 13:22
  • The classical reference on this is Ito & Mester 1986 "The phonology of voicing in Japanese", Linguistic Inquiry 17:49–73
    – user6726
    Commented Nov 11, 2016 at 17:59
  • @lemontree How come?
    – Alenanno
    Commented Nov 13, 2016 at 13:11
  • @Alenanno Because it's about Japanese?! Commented Nov 13, 2016 at 15:19
  • @lemontree Uhm, but we don't migrate questions about English to EL&U simply because they're about English. We do it when they're about usage, for example. This one is asking about an aspect of Japanese morphology. I may concede that it could also be on topic on Japanese SE (not sure), but even if it was, it wouldn't make it off topic here.
    – Alenanno
    Commented Nov 13, 2016 at 16:01

1 Answer 1


This phenomenon is called rendaku, or "sequential voicing".

Many phonemes in Japanese occur in voiced/unvoiced pairs. In kana writing, these are distinguished with a dakuten "voice mark" over the voiced version: for instance, か /ka/, が /ga/.

(Side note: in a few cases this reflects historical rather than current pronunciation: /h/ voices to /b/ because it was originally /ɸ/, and /β/ isn't distinguished from /b/.)

Rendaku means that the first sound in the second part of a compound becomes voiced...most of the time. In reality, it's not quite this simple. There are a few additional rules:

  • Branching constraints! This is what the NACLO problem is about.
  • If the sound is already voiced, nothing happens to it
  • Lyman's Law: rendaku doesn't happen if the second word contains any voiced obstruents
  • Rendaku also doesn't happen in "A and B" compounds: so yama "mountain" + kawa "river" could become yamakawa "mountain and river" or yamagawa "river which is on a mountain"

So as you can see, rendaku isn't completely free from ambiguity. Already-voiced sounds such as /n/, /r/, /j/ aren't affected by it at all, which is what the footnote in the problem is pointing out. But there are also specific words which completely ignore rendaku, or which cause it to happen inconsistently. A few roots become voiced when attached to nouns, but not to verbs. It doesn't help that this voicing isn't indicated at all in kanji writing.

In these cases, the ambiguity has to be resolved the same way as in English: context, world-knowledge, and familiarity with the language.

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