In English, making a verb "can" leaves its object untouched: I eat bread → I can eat bread. Japanese does something no English speaker expects. When a verb goes into the potential form, the direct object that took を often re-marks to が:
- パンを食べる → パンが食べられる
- 日本語を話す → 日本語が話せる
This particle shift is one of the most reliable "tells" that separates natural Japanese from textbook-literal Japanese, and it flows from a single idea you already met in the overview: the potential is stative.
The shift in a nutshell
Take the object of the plain verb, switch を to が, and put the verb in the potential:
| Plain (action) | Potential (ability) | Reading |
|---|---|---|
| 車を運転する | 車が運転できる | kuruma o unten suru → kuruma ga unten dekiru |
| 漢字を読む | 漢字が読める | kanji o yomu → kanji ga yomeru |
| お酒を飲む | お酒が飲める | osake o nomu → osake ga nomeru |
兄は車が運転できるけど、私はまだ自転車しか乗れない。
ani wa kuruma ga unten dekiru kedo, watashi wa mada jitensha shika norenai
My brother can drive a car, but I can still only ride a bicycle.
最近、漢字がだいぶ読めるようになった。
saikin, kanji ga daibu yomeru yō ni natta
Lately I've become able to read a fair amount of kanji.
お酒が飲めないので、ウーロン茶をお願いします。
osake ga nomenai node, ūroncha o onegai shimasu
I can't drink alcohol, so I'll have oolong tea.
Why が: the potential is stative
The deep reason is not arbitrary. A potential describes a standing state — an ability or a possibility — not an action performed on an object. "I can eat bread" is closer in meaning to "bread is edible to me" than to "I act on bread." In that reading, the bread isn't really a patient being acted upon; it behaves like the subject of an adjective of ability, and Japanese marks such subjects with が — the same が that heads 好き ("私は寿司が好き", "I like sushi") and 上手 ("彼は料理が上手", "he's good at cooking"). The potential joins that family.
The person is the topic (は); the thing is が
A common beginner tangle is trying to give the person が. In a full sentence the person is usually the topic with は, and the thing gets が:
私は 日本語が 話せる。 — "As for me, Japanese is speakable." (I can speak Japanese.)
Two different particles doing two different jobs: は frames who we're talking about; が marks the ability's object.
私は辛いものが食べられないんです。
watashi wa karai mono ga taberarenai n desu
I can't eat spicy food.
ピアノが弾けるなんて、すごいね。
piano ga hikeru nante, sugoi ne
You can play the piano? That's amazing.
ここでは写真が撮れますか。
koko de wa shashin ga toremasu ka
Can I take photos here?
When を survives: it's a real choice, not a hard rule
Here is the honest, insight-level part that many sources flatten into "always use が." が is the default, but を is genuinely acceptable in several situations — the choice is real and meaning-bearing:
1. The action or effort is emphasized. When you're stressing the doing, not the standing ability, を feels right.
こんなに難しい問題を、よく一人で解けたね。
konna ni muzukashii mondai o, yoku hitori de toketa ne
You actually managed to solve such a hard problem all by yourself — impressive.
2. A long, complex, or distant object. When lots of material sits between the object and the potential verb, を keeps the sentence readable and が can sound clumsy.
3. Avoiding a が pile-up. If the clause already has a が subject, adding a second が for the object grates. Keeping を on the object neatly sidesteps the "double-が" clash.
誰がこんな重い荷物を一人で運べるの?
dare ga konna omoi nimotsu o hitori de hakoberu no?
Who could carry such heavy luggage all by themselves?
Here 誰が is the subject, so the object stays 荷物を — two が in one clause (×誰が荷物が) would be unnatural.
4. Inside 〜ことができる, keep を. In the fuller frame 〜ことができる, the object belongs to the dictionary-form verb tucked inside こと, so it keeps its normal を: 日本語を話すことができる. The が-shift is a property of the one-word potential, not of ことができる.
この試験に合格すれば、日本語を教えることができる。
kono shiken ni gōkaku sureba, nihongo o oshieru koto ga dekiru
If you pass this exam, you'll be able to teach Japanese.
できる with a noun also takes が
The suppletive potential できる pairs the ability's object with が in the same way: 運転が上手 / 運転ができる. In the common compound pattern the whole noun+する fuses, and the object of the noun re-marks: 車が運転できる.
日本語がまだうまく話せないので、ゆっくり話してもらえますか。
nihongo ga mada umaku hanasenai node, yukkuri hanashite moraemasu ka
I can't speak Japanese well yet, so could you speak slowly?
Common mistakes
❌ 私が日本語を話せます。
watashi ga nihongo o hanasemasu
Incorrect — the person should be topic (は), and the ability's object defaults to が, not を.
✅ 私は日本語が話せます。
watashi wa nihongo ga hanasemasu
I can speak Japanese.
Double-wrong: が on the person, を on the object. Flip both — は on the person, が on the thing.
❌ 甘いものをあまり食べられない。
amai mono o amari taberarenai
Understandable, but the textbook default re-marks the object to が.
✅ 甘いものがあまり食べられない。
amai mono ga amari taberarenai
I can't eat many sweets.
Mechanically keeping を because English keeps its object is the classic transfer slip. You'll hear を, but が is the safe default in careful speech.
❌ 日本語が話すことができる。
nihongo ga hanasu koto ga dekiru
Incorrect — inside 〜ことができる the embedded verb 話す keeps its own を.
✅ 日本語を話すことができる。
nihongo o hanasu koto ga dekiru
I'm able to speak Japanese.
Don't over-apply the が-shift. It belongs to the one-word potential (話せる), not to the dictionary verb sitting inside ことができる.
❌ 誰がこの漢字が読めますか。
dare ga kono kanji ga yomemasu ka
Incorrect — with a が subject already present, stacking a second が on the object is unnatural; keep を.
✅ 誰がこの漢字を読めますか。
dare ga kono kanji o yomemasu ka
Who can read this kanji?
Key takeaways
- A potential verb usually re-marks its object from を to が: パンが食べられる, 日本語が話せる.
- The reason is stativity — the object behaves like the subject of an adjective of ability ("bread is edible-to-me"), the same が as 好き and 上手.
- In a full sentence, the person is topic (は) and the thing is が: 私は日本語が話せる.
- を survives when the action is stressed, the object is long/distant, a が subject is already present, or inside 〜ことができる — a genuine choice, not a rule to force.
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Start learning Japanese→Related Topics
- The Potential Form: Expressing 'Can'N4 — An introduction to the potential form 可能形 — the stative conjugation that turns a verb into 'can / is able to,' and why its object leans toward が.
- が: The Subject MarkerN5 — How が marks the grammatical subject — presenting new information, answering 'who/what?', and marking the が-object of stative predicates like 好き, 分かる, and できる.
- 〜ことができる: The Analytic PotentialN4 — The periphrastic potential — dictionary-form verb + ことができる — a heavier, more explicit way to say 'can' that rules the written and formal register while the short potential owns speech.