Your brother eats sweets every day, and his teeth start to hurt. In English and Chinese, you can just say "his teeth hurt" and be done. Japanese doesn't work that way — you must add なる to express "they weren't hurting before, but now they are because of something."
This is one of the biggest differences between Japanese and Chinese/English: Japanese is very particular about state changes.
The Basic Rule
Depending on the word type that comes before it, なる connects differently:
| Word type | Connection | Example |
|---|---|---|
| い-adjective | い → くなる | 痛い → 痛くなる (become painful) |
| な-adjective | な → になる | 好き → 好きになる (come to like) |
| Noun | Noun + になる | 医者 → 医者になる (become a doctor) |
い-adjective + くなる
Drop the い, add くなる:
お腹が痛くなった。 → My stomach started hurting.
最近、寒くなりましたね。 → It's gotten cold recently, hasn't it?
歯が痛くなった。 → My teeth started hurting.
Key point: The stomach wasn't hurting before — it became painful because of eating too much. Japanese requires なる to express this transition from one state to another.
な-adjective + になる
Drop the な, add になる:
日本のアニメを見て、日本語が好きになりました。 → After watching Japanese anime, I came to like Japanese.
部屋がきれいになった。 → The room became clean.
Key point: 好きになった means you didn't like it before (or had no feeling about it), and then developed a liking for it.
Noun + になる
弟は医者になりました。 → My brother became a doctor.
来年、大学生になります。 → Next year I'll become a university student.
The Gap Between Japanese and Chinese/English Thinking
In Chinese, you say "my brother eats sweets every day, his teeth hurt" and that's it. But a Japanese speaker's brain works like this:
His teeth weren't hurting originally, right? → It's because of eating sweets that they started hurting → Must use なる
So in Japanese, you must write:
弟は毎日甘い物を食べたので、歯が痛くなりました。
Writing 「歯が痛いです」 without なる isn't wrong per se, but it means "my teeth hurt (as a current fact)" — there's no sense of change. Adding なる conveys the transformation.
More examples:
| English | Japanese (with なる) | Logic |
|---|---|---|
| My stomach started hurting | お腹が痛くなった | Wasn't hurting → became painful |
| I came to like Japanese | 日本語が好きになった | Had no feeling → came to like it |
| It got cold | 寒くなった | Wasn't cold → became cold |
Bonus: Verb Nominalization
The lesson also covered a related point: dropping ます from the ます-form turns a verb into a noun.
| Verb | ます-form | Nominalized | Meaning |
|---|---|---|---|
| 食べすぎる | 食べすぎます | 食べすぎ | overeating |
| 行く | 行きます | 行き | the way there |
| 帰る | 帰ります | 帰り | the way back |
食べすぎですよ。 → You've been overeating! (食べすぎ is a noun, so it can take です)
行きはバスで、帰りはタクシーです。 → I take the bus on the way there and a taxi on the way back.
The verb's second conjugation form (ます-form minus ます) → becomes a noun → can then take です. This is why 食べすぎ can be directly followed by です.
Summary
- い-adjective → くなる; な-adjective / noun → になる
- なる expresses the transition from state A to state B
- Japanese is very particular about change: it wasn't like this before, something caused it to change → must use なる
- Verb ます-form minus ます → noun; can then take です
Practice Questions
Q1. How do you say "after watching Japanese anime, I came to like Japanese" in Japanese?
Answer
日本のアニメを見て、日本語が好きになりました。 好き is a な-adjective, so it takes になる.
Q2. Why can't you just use 「お腹が痛いです」 to express "my stomach started hurting"?
Answer
「お腹が痛いです」 states the current condition ("my stomach hurts") without any sense of change. To express "it wasn't hurting before but started hurting because of something," you need お腹が痛くなりました with なる.
Q3. What part of speech is 「食べすぎ」in「食べすぎですよ」? Where does it come from?
Answer
食べすぎ is a noun. It comes from the verb 食べすぎる — take the ます-form (食べすぎます), drop ます, and you get a noun. This is why it can be followed by です.