For learners of Japanese, mastering kanji and kana is often seen as one of the biggest challenges. But beyond writing, the sound system of Japanese also hides many fascinating rules. One of these is rendaku.
For example:
・さかな (sakana, fish) begins with a clear sound, but when combined with やき (yaki, to grill), it becomes やきざかな (yakizakana, grilled fish).
However, not all compounds trigger rendaku. You say やきさば (yakisaba, grilled mackerel) but not yakizaba. In other words, rendaku has patterns, but it also includes exceptions that make it less straightforward.
What is Rendaku and Why Does It Happen?
What is Rendaku?
Rendaku is a sound change that occurs in Japanese compounds. When two words are combined, the initial consonant of the second element may change from k, s, t, h to g, z, d, b.
Why does this happen?
・Assimilation: A voiceless consonant between vowels naturally becomes voiced, making pronunciation smoother.
・Historical background: In old Japanese, words rarely began with voiced consonants. By adding voicing inside compounds, speakers could signal that the words were joined together.
Examples:
・やき＋さかな → やきざかな (yakizakana, grilled fish)
・はな＋ひ → はなび (hanabi, fireworks)
・て＋かみ → てがみ (tegami, letter)
・ほし＋そら → ほしぞら (hoshizora, starry sky)
When Rendaku Does Not Occur
Lyman’s Law
If the second element already contains a voiced consonant, rendaku does not occur.
・はる＋かぜ → はるかぜ (harukaze, spring breeze)
・おお＋とかげ → おおとかげ (ootokage, large lizard)
Word Origin
Rendaku occurs most frequently in native Japanese words, but it behaves differently in Sino-Japanese compounds and loanwords.
・Native: やき＋さかな → やきざかな (yakizakana). This is the regular pattern.
・Sino-Japanese: かぶしき＋かいしゃ → かぶしきがいしゃ (kabushikigaisha, corporation).
This is an exception, since Sino-Japanese words rarely undergo rendaku.
・Loanword: あま＋かっぱ → あまがっぱ (amagappa, raincoat).
This is also an exception, because loanwords almost never take rendaku. Only older
borrowings sometimes allow it.
Semantic Relationship
If the two elements are parallel, rendaku is unlikely. If one modifies the other, it is more likely.
・やま＋かわ → やまかわ (yamakawa, mountains and rivers, parallel, no rendaku)
・やま＋かわ → やまがわ (yamagawa, river in the mountains, modifying, rendaku)
・すき＋きらい → すききらい (sukikirai, likes and dislikes, no rendaku)
・くわず＋きらい → くわずぎらい (kuwazugirai, dislike of something without trying it, rendaku)
Compound Structure
In compounds of three or more elements, rendaku depends on which parts combine first and where the internal “unit” is formed.
・[[お＋しろ]＋わし] → おじろわし (ojirowashi, white-tailed eagle). The inner unit is お＋しろ (oshiro). Here, し changes to じ, giving おじろ, and then わし (eagle) attaches.
・[もん＋[しろ＋ちょう]] → もんしろちょう (monshirochou, cabbage butterfly). In this case, しろ＋ちょう forms the unit 白蝶 (shirochou, white butterfly). Because し is the first element inside that unit, it does not undergo rendaku.
Regional Variation and Surnames
Rendaku also appears in surnames, but usage may vary regionally. The surname 山崎 is often read やまざき (Yamazaki) in eastern Japan and やまさき (Yamasaki) in western Japan.
In addition, some words allow both voiced and unvoiced forms, such as 奥深い (okubukai / okufukai, profound), reflecting historical variation.
Special Cases
Verb Compounds
In verb + verb compounds like 追いかける (oikakeru, to chase) or 積み重ねる (tsumikasaneru, to pile up), rendaku usually does not occur.
Sino-Japanese Verbs
Some Sino-Japanese verbs ending in する shift to ずる. Examples: 感ずる (kanzuru), 演ずる (enzuru), 講ずる (kouzuru). Today, these are often replaced by forms like 感じる (kanjiru) and 演じる (enjiru).
Accent
Compounds with rendaku often shift toward a flat intonation pattern.
Examples:
・やま＋さと → やまざと (yamazato, mountain village)
・ほし＋そら → ほしぞら (hoshizora, starry sky)
・いし＋ばし → いしばし (ishibashi, stone bridge)
Final Thoughts
Rendaku is one of the most intriguing sound changes in Japanese. It is partly rule-based but also unpredictable.
For learners, the goal is not to memorize every exception, but to develop an ear for natural usage. By paying attention to how words appear in conversation, surnames, and dictionaries, you will gradually build an intuition for when voicing feels natural.
Next time you encounter a new compound, ask yourself: will it rendaku or not? That small habit will help you better understand this fascinating feature of Japanese phonology.