Rendaku in Japanese: Why かみ Becomes がみ, and How to Hear It

Your friend says 昨日、祖母に手紙を書きました (kinou, sobo ni tegami wo kakimashita), and somewhere in the middle you lose the thread. Grandmother, wrote, yesterday. What was tegami? You know 手 (te, hand). You know 紙 (kami, paper). You have known both for a year. But the word in the sentence was gami, and your ear was waiting for kami.

That shift has a name: rendaku (連濁), or sequential voicing. When Japanese glues two words into one, the first consonant of the second word often picks up voicing. K turns into g, s into z, t into d, h into b. Tofugu's guide teaches it as a set of rules for predicting readings. This post treats it as a listening problem: the four swaps, how to run them backwards when you hear a word you don't recognize, the one brake that almost never fails, and where the rules run out.

What rendaku does: four consonant swaps, one direction

折り紙 is origami, not orikami. 青空 (blue sky) is aozora, built from sora. 本棚 (bookshelf) is hondana, built from tana. 花火 (fireworks) is hanabi: flower plus hi, fire.

That little pair of dots (゛, dakuten) is how you write the change. Rendaku is the change itself.

Notice h goes to b, never p. That looks odd until you learn that Japanese h descends from an older p sound, and b is the voiced partner of p (Wikipedia, "Rendaku"). So 人々 is hitobito and 切り花 (cut flowers) is kiribana. If you've met the p in いっぽん (one long thing) and the b in さんぼん (three), those come from a different set of changes, covered in the post on Japanese counters. さんぼん is probably a look-alike: voicing after ん with its own history, which Wikipedia, citing Mark Irwin, describes with 東国 (tōgoku).

The same change runs in the other direction when you speak. Build 手紙 from its parts and you'll say tekami, which a listener will understand and immediately notice.

For a listener, the voicing is a useful clue in itself: it only happens inside a compound, so ひとびと is one word, "people," while ひと、ひと is two. Why Japanese does this at all is less certain. One leading idea is that a linking の shrank to a nasal sound that voiced the next consonant, so yama-no-tori became やまどり (copper pheasant). The Japanese Wikipedia article on 連濁 says plainly that nothing certain is known.

Why you don't recognize 手紙 when you hear it

居酒屋 is izakaya, and you've probably said it a hundred times without spotting 酒屋 (sakaya, liquor shop) inside it. That's the listening problem in one word. Your memory files the word under sakaya. The sentence hands you zakaya. Nothing connects them unless you make the connection on purpose.

Two things make it harder than the kana suggest.

First, the g in the middle of a word often isn't a hard g. Some speakers, mostly older ones and people from north-eastern Japan, turn it into the ng of English "singer." This is called 鼻濁音 (bidakuon), and it's getting rarer among younger speakers. Many others soften g, d and b between vowels until they're barely a stop at all (Wikipedia, "Japanese phonology"). So 手紙 can reach you as something close to te-ngami. If you only listen for a crisp g, you'll miss it.

Second, two of the voiced kana are spelled one way and heard another. When rendaku voices つ or ち, the spelling becomes づ or ぢ: 三日月 (crescent moon) is みかづき, 鼻血 (nosebleed) is はなぢ, 手作り (handmade) is てづくり. In standard Tokyo speech, づ sounds exactly like ず and ぢ exactly like じ (Wikipedia, "Yotsugana"). Your ear hears zu.

How to undo rendaku while you listen

When a word goes past you and it has g, z, j, d or b right where a second word would start, strip the voicing and see what's left:

• hear g → try k: くちぐせ (pet phrase) → くせ, habit
• hear z → try s and ts: まきずし (rolled sushi) → すし; みかづき → つき
• hear j → try sh and ch: はなぢ → ち, blood
• hear d → try t: ときどき (sometimes) → とき, time
• hear b → try h, never p: はなび → ひ, fire

Here it is in three everyday sentences:

• 週末は時々ジムに行きます。Shuumatsu wa tokidoki jimu ni ikimasu. I sometimes go to the gym on weekends. Toki-doki: time, time.
• 今年の花火大会、一緒に行かない？Kotoshi no hanabi taikai, issho ni ikanai? Want to go to the fireworks festival together this year? Hana-bi: flower, fire.
• 回転寿司でも巻き寿司は頼む。Kaitenzushi demo makizushi wa tanomu. Even at conveyor-belt sushi, I order rolls. Maki-zushi: roll, sushi. You'll also hear kaitensushi; both are in the dictionary.

It feels slow at first. It stops feeling slow once you've pulled 酒屋 out of 居酒屋 and 棚 out of 本棚 a few times, because then zakaya and dana start to register as words you already own.

Lyman's Law: when the second word already has g, z, d or b

山火事 (forest fire) is yamakaji, not yamagaji. 火事 already has a voiced sound in it, the j of じ, and Japanese won't add a second one. That brake is called Lyman's Law, and it's the most dependable rule in this post.

The j counts because じ is just the z row before i. "Anywhere" means anywhere. 蜥蜴 (lizard) is とかげ, with the g in the third syllable, and 大蜥蜴 is still おおとかげ. 春風 (spring breeze) is はるかぜ, because 風 already has a z. Only those four sounds count. M, n and r don't block anything, which is why かみ, たな and そら all voice freely.

For listening, the law gives you permission to relax. If the second half of a compound you hear already has a voiced sound in it, its first sound is exactly what it seems to be. You don't need to undo anything.

The law is named after Benjamin Smith Lyman, an American who described it in 1894, but Edo-period scholars Kamo no Mabuchi and Motoori Norinaga had spotted it in the 1700s (Wikipedia, "Rendaku"). It isn't perfect. 縄梯子 (rope ladder) is なわばしご, even though はしご has a g. Exceptions like that are rare enough to learn one at a time.

Which compounds resist rendaku, and how much to trust each rule

大好き is daisuki. Not daizuki. The voicing doesn't always come, so it helps to know how far each rule goes, from the one you can bet on to the ones you can't.

Lyman's Law is the one you can bet on. The Wikipedia article on rendaku, citing the linguist Mark Irwin, calls it "highly reliable, with only a small number of exceptions."

Next comes a strong tendency: native words voice, Sino-Japanese words mostly don't. Words of Japanese origin (かみ, そら, たな) take rendaku often. Words borrowed from Chinese, the ones you read with on'yomi, mostly resist. Irwin counted only about 20% of single-kanji Sino-Japanese roots and 10% of two-kanji ones that voice in at least some compounds. The exception you'll actually hear is 会社 (kaisha, company). It's がいしゃ in 株式会社 (kabushiki-gaisha, the "Inc." in countless company names) and in 親会社 (oyagaisha, parent company). Modern loanwords almost never voice. A few very old Portuguese ones do: 雨合羽 (raincoat) is あまがっぱ, from capa (連濁).

"X and Y" compounds tend not to voice, though this one is weaker. 山川 read as やまがわ is a mountain stream. Read as やまかわ, it's "mountains and rivers." Same kanji, and the voicing tells you which one you heard. 好き嫌い (likes and dislikes) stays すききらい.

Sound-effect words never voice. ときどき does because it's two nouns, toki and toki. きらきら (sparkle) and ころころ (rolling) are onomatopoeia, and they keep their second half exactly as it is.

Everything else you learn word by word. The Japanese Wikipedia article on 連濁 says it can't be fully predicted, at least in modern Japanese, and the NINJAL Rendaku Project filled a whole volume with the factors that push it one way or the other. 大好き stays suki. That's just what the word does.

A five-minute reverse-rendaku drill

口癖 is kuchiguse: kuchi plus kuse, mouth plus habit. Say each of these out loud, split it into two words you know, then check the answers below:

• てがみ
• あおぞら
• みかづき
• いざかや
• ひがさ

Answers: て + かみ, あお + そら, みか + つき, い + さかや, and ひ + かさ (a parasol is a sun umbrella).

Then say pairs back to back, the bare word and the compound: かさ / ひがさ, そら / あおぞら, たな / ほんだな, ひと / ひとびと. Same word, two shapes.

One honest limit: this only works for words you already know, so if you've never met さかや, no drill will pull it out of いざかや. What the drill fixes is the case that stings. A word you studied goes past you in a sentence while you're still waiting for a k that never comes.

Next time someone suggests an izakaya after work, listen for the sakaya inside it. It's been there the whole time.