づ vs ず (and ぢ vs じ): The Japanese Spelling Rule for Yotsugana
づ and ず sound identical. So do ぢ and じ. Yet 水 is written みず and 続く is written つづく — and getting it wrong is a classic mistake (even for natives, and for the IME). These four kana are called yotsugana (四つ仮名), and the rule for choosing between them is refreshingly simple.
The Default: Always ず and じ
In modern Japanese spelling (現代仮名遣い), the “zu” sound is written ず and the “ji” sound is written じ — unless one of two specific exceptions applies. When in doubt, use ず/じ.
Exception 1: Rendaku (連濁)
When a word that begins with つ or ち joins a compound and becomes voiced, it turns into づ or ぢ — keeping its connection to the original word.
| Original word | Compound | Reading |
|---|---|---|
| 月（つき） | 三日月 | みかづき (crescent moon) |
| 遣い（つかい） | 小遣い | こづかい (pocket money) |
| 作り（つくり） | 手作り | てづくり (handmade) |
| 血（ち） | 鼻血 | はなぢ (nosebleed) |
| 力（ちから） | 底力 | そこぢから (latent strength) |
つ → づ, ち → ぢ. The voiced kana “points back” to the word it came from.
Exception 2: Repeated つ / ち
When つ or ち is repeated within a word and the second one voices, it is written づ / ぢ.
つ + つく — repeated つ
ち + ちむ — repeated ち
Words People Get Wrong
repeated つ (Exception 2)
「地」 on-reading is じ — not rendaku
modern standard is ず (いなづま also accepted)
Typing & Checking
On a romaji keyboard: ず = zu, づ = du, じ = ji, ぢ = di.
Let the IME confirm you: type tuduku and 続く appears; tuzuku will not convert to it. If the kanji you expect does not come up, your kana is wrong.
Teacher’s Note
Boil it down to one sentence: default to ず/じ; use づ/ぢ only when the sound comes from a つ/ち (rendaku) or a repeated つ/ち. Watch 地面 (じめん) — the じ is an on-reading, not rendaku, so it is じ, not ぢ.
Frequently Asked Questions
When do you use づ instead of ず?
Default to ず. Use づ only in two cases: rendaku, where a word starting with つ gets voiced inside a compound (手 + 作り → てづくり), and repetition, where つ follows つ in the same word (続く → つづく). Everything else is spelled with ず.
Is there any pronunciation difference between づ and ず?
In modern standard Japanese, no — づ and ず are pronounced identically, as are ぢ and じ. These four kana are called yotsugana. The distinction survives only in spelling, which is why the rule has to be memorized.
Why is 鼻血 written はなぢ and not はなじ?
Because it is rendaku: 鼻 (はな) + 血 (ち) — the ち of 血 gets voiced to ぢ inside the compound. Since the original kana is ち, the voiced spelling keeps its shape as ぢ rather than じ.
Spell it right, every time
Nihongo Pass pairs every word with its correct reading and audio — so づ/ず and ぢ/じ stop being a guessing game.
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