You've learned the basic particles (が・を・に・で) and think you've got them down. Then you encounter passive, causative, and ～たい — and suddenly all the particles rearrange.
「酒を飲む」 (drink sake) → 「酒が飲みたい」 (want to drink sake)
Why did を become が? It's not random — there's a system behind it.
Core Principle: The New Subject Gets が
Japanese sentence structure revolves around one rule: the subject gets が. When the sentence's perspective shifts (e.g., active → passive), the subject changes, and particles must be redistributed.
To understand any particle swap, ask two questions:
- Who is the new subject? → That person/thing gets が
- What happens to the displaced particle? → It changes to something else
Passive: を → が, が → に
Passive flips the perspective from the doer to the receiver.
Basic Passive (Transitive Verbs)
| Active | Passive |
|---|---|
| 三田が 吉田を 殴る。 | 吉田が 三田に 殴られる。 |
| Mita hits Yoshida. | Yoshida is hit by Mita. |
The swap rules:
- The original object (吉田を) becomes the subject → を → が
- The original subject (三田が) becomes the agent → が → に
Memory aid: Passive = the object rises to become the subject. を upgrades to が; the old subject が steps down to に.
Indirect Passive with Intransitive Verbs (迷惑受身)
Intransitive verbs have no object, but Japanese can use "indirect passive" to express being negatively affected:
| Original | Passive (adversative) |
|---|---|
| 雨が降る。 It rains. | 私は雨に降られた。 I got rained on. |
| 隣の人が騒ぐ。 The neighbor is noisy. | 私は隣の人に騒がれた。 I was bothered by the noisy neighbor. |
A new "victim" becomes the subject (私は), and the original subject becomes に.
Causative: が → を or が → に
Causative means "make/let someone do something." The person who used to act independently now becomes the one being commanded.
Intransitive Verb Causative: が → を
| Original | Causative |
|---|---|
| 弟が行く。 Brother goes. | 母が 弟を 行かせる。 Mom makes brother go. |
| 学生が走る。 Students run. | 先生が 学生を 走らせる。 Teacher makes students run. |
Intransitive verbs have no object, so the を slot is empty — the causee fits right in with を.
Transitive Verb Causative: が → に
| Original | Causative |
|---|---|
| 係者が 業者を催促する。 The person in charge presses the vendor. | 課長が 係者に 業者を催促させる。 The section chief makes the person in charge press the vendor. |
Transitive verbs already have を (業者を催促する), so you can't add another を — the causee uses に instead.
Key Rule: One Verb Cannot Have Two を
This is an iron rule of Japanese grammar. When causative + movement space both need を:
| Problem | Fix |
|---|---|
| ×先生が 学生を グラウンドを走らせる。 | ○先生が 学生に グラウンドを走らせる。 |
グラウンドを走る (run on the field) needs its を for the movement space, so the causee must yield and take に instead.
Priority: Movement-space を > Causee を. When they conflict, the causee switches を → に.
～たい (Want to): を → が
When expressing desire, the object's を can become が:
| Original | ～たい |
|---|---|
| 酒を飲む。 Drink sake. | 酒が飲みたい。 Want to drink sake. |
| 寿司を食べる。 Eat sushi. | 寿司が食べたい。 Want to eat sushi. |
Why? Because ～たい is adjectival (it describes a psychological state, not an action). The thing you want becomes the subject of the state, so it takes が.
In practice, both を and が work with ～たい, but が sounds more natural in conversation. を is common in writing and exams.
Potential Form: を → が
Similar to ～たい, potential forms tend to swap を for が:
| Original | Potential |
|---|---|
| 日本語を話す。 Speak Japanese. | 日本語が話せる。 Can speak Japanese. |
| 漢字を読む。 Read kanji. | 漢字が読める。 Can read kanji. |
Same logic: potential emphasizes "what is possible" — the object becomes the subject of the ability.
Complete Swap Table
| Grammar Change | Original → New | Explanation |
|---|---|---|
| Passive (transitive) | を → が | Object becomes subject |
| Passive (transitive) | が → に | Subject becomes agent |
| Causative (intransitive) | が → を | Causee takes empty を slot |
| Causative (transitive) | が → に | を already taken; causee uses に |
| Causative + movement を | を (causee) → に | Two を conflict; causee yields |
| ～たい | を → が | Object becomes subject of desire |
| Potential | を → が | Object becomes subject of ability |
Summary
- Passive: Object rises to subject (を→が); original subject steps down (が→に)
- Causative with intransitive: causee uses を (the slot is empty)
- Causative with transitive: causee uses に (を is taken)
- Iron rule: One verb cannot have two を — when they conflict, the causee yields を→に
- ～たい / Potential: object を→が (becomes the subject of a state)
- All swaps follow one principle: the new subject gets が, and everything else redistributes
Practice Questions
Q1. Convert 「三田が吉田を殴る」 to passive.
Show answer
吉田が三田に殴られる。 (Yoshida is hit by Mita.)
吉田 (を) becomes the subject → が. 三田 (が) becomes the agent → に. Verb becomes passive: 殴る → 殴られる.
Q2. 「先生が学生を走らせる」— how do you add "on the field" (グラウンドを走る)?
Show answer
先生が学生にグラウンドを走らせる。
Can't have two を, so 学生を → 学生に. The movement-space を takes priority.
Q3. How do you say "want to drink beer" from 「ビールを飲む」?
Show answer
ビールが飲みたい。 (You can also say ビールを飲みたい, but が is more natural.)
～たい is adjectival, so the object becomes the subject of the desire: を → が.