じ vs. ぢ & ず vs. づ: When do we use which?（四つ仮名）

Choppa

Harada-sensei! Why do we say にほんじん instead of にほんぢん while
we say はなぢ instead of はなじ?

That's a great question!
Japanese has another case like that between ず and づ!
There are some rules which you can use to decide which hiragana to use.
I will introduce those!!

Harada-sensei

Choppa

はい、お願いします！

じ vs. ぢ: When do we use which?

In this section, I will explain when じ/ず should be used instead of ぢ/づ in Tokyo dialects (in some dialects in Japanese such as Kochi, Miyazaki, and Kagoshima dialects, those four letters are pronounced differently). There are same rules with respect to the use of じ vs. ぢ and ず vs. づ、and I explain those in turn.

The following box shows when じ/ぢ should be used, where 'ZI' refers to a letter pronounced じ or ぢ (e.g., いちZI 'one o'clock'), whose right form you are curious about. When you examine the right form of ZI, you can check each of the following four rules IN THE ORDER; i.e., check Rule 1. If the statement of the if-clause is irrelevant, check Rule 2. If the statement of the if-clause is irrelevant, check Rule 3. If the statement of the if-clause is irrelevant, check Rule 4.

As Rule 4 says, じ/ぢ is generally prioritized. Moreover, there are some exceptions for the above rules, as shown below. So it is safer to use じ/ぢ when in doubt. But the rules work for many words, so you could look at the details of the rules below.

Rule 3

Rule 3 says that if ZI is the voiced counterpart of し/ち due to rendaku, use じ/ぢ. Suppose that there is a word あいうZIえお. If the meaning of the word consists of the meanings of the word あいう and the word しえお, then use じ for ZI (e.g., いろじろ = いろ+しろ). Likewise, if the meaning of the word あいうZIえお consists of the meanings of the word あいう and the word ちえお, then use じ for ZI (e.g., はなぢ = はな+ち).

Now, consider いちじるしい, which looks prima facie surprising because ち precedes じ; according to Rule 2, it seems that the right form is いちぢるしい. Here comes etymology again! There is a view that いちじるしい comes from いち+しるし, and the first し becomes じ due to renduku, just like いろじろ above. Isn't it interesting?!

Here's another interesting word: せかいじゅう（世界中）. 中 has ちゅう as its basic hiragana form, so one may wonder why せかいぢゅう is the right form, where ぢ is derived from ち of ちゅう via rendaku. My answer to this question is that 中 has じゅう as its basic hiragana form, so せかいじゅう is the 'preferred' form (it seems that せかいぢゅう is not incorrect form, though it doesn't look great to me).

Lastly, consider also

ONE PIECE STRONG WORDS 下巻 <ヴィジュアル版> (集英社新書)

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Note: I've attached the above comic page including the target word (i.e., たしぎぢゃん) as One Piece is very popular among Japanese language leaners and I wanted to introduce how the relevant grammar point is used in real life. If there is any copyright issue with the picture, I will immediately delete it. Otherwise, thank you very much for your help and great comic!!

As shown above, there are basic rules about the use of じ/ぢ, but there are some 'exceptions'. For instance, some proper names such as ブリヂストン (Bridgestone), 大人のラヂオ (a radio program), スタジオ ヂーニアス (fitness club) uses ヂ although ジ should be used according to the above rules. So you could use the above rules as a baseline, and memorize exceptions!

ず vs. づ: When do we use which?

For ずvs.づ, ず and づ behave in the same way as じ and ぢ, respectively, as summarized below. So I do not go into the details of each rule, but I briefly discuss two tricky data.

First, in relation to Rule2, consider みっつずつ (わたしはペンとかばんをみっつずつかう。'I'll buy three for each of pens and bags.'); we use ず instead of づ despite it being preceded by つ. Why is that? This is because according to Rule2 づ should not be used if there is a word boundary immediately before ZU, and this is the case in みっつずつ , which can be decomposed into みっつ 'three' and ずつ 'each'.

Next, consider いなずま（稲妻）’thunder' in relation to Rule3. As you can see from the kanji, いなずま consists of two words いね(rice) and つま'wife'. Since the latter word starts with つ, why don't we write いなづま? One potential answer to this question is that いなずま has a unique characteristics compared to さばずして, づくり that the meaning of the word has little to do with rice and wife (although there is some etymological story behind the use of kanji and づ, which most Japanese do not know and thus which is less likely to be the reason why we use づ). This hypothesis is compatible with the fact that we write other people's wife and new wife as ひとづま（人妻）and にいづま（新妻）. The meaning of ひとづま consists of ひと '(other) person' and つま 'wife' and the meaning of にいづま consists of にい 'new' and つま 'wife'. However, if this hypothesis is right, how can we explain the use of ず in かたず（固唾）'saliva you get when you are nervous', which consists of かた 'hard' and つば 'saliva'? At first glance, the meaning of かたず has little to do with hard and saliva, but one can think of かたず as the saliva when you are nervous, in which your body is likely to be 'hardened' (i.e., you clam up). After all, orthography is not a natural thing, but an artificial thing made up by humans. So we may be just seeing irregular examples, do you see some pattern those 'irregularities'?

Lists of words with じ/ぢ and ず/づ in Genki I (third edition) and Tobira

I will introduce words with じ, ぢ, ず, or づ that are used in Genki I (3rd edition) and Tobira in turn.

References

• 現代仮名遣い　本文　第2（表記の慣習による特例）, Agency for Cultural Affairs, Government of Japan.