To say "can" in English you bolt an unchanging little modal — can — in front of the verb, and the verb never moves: swim → can swim, read → can read. Japanese does something structurally different. It conjugates the verb itself into a brand-new form, the potential form (可能形, かのうけい): 泳ぐ (oyogu, "swim") becomes 泳げる (oyogeru, "can swim"); 話す (hanasu, "speak") becomes 話せる (hanaseru, "can speak"). This page explains what that form means and why it behaves the way it does; the mechanics of building it, class by class, live on the potential formation page.
What the potential expresses: ability and possibility
可能形 covers the whole English span of "be able to" — both personal ability and circumstantial possibility.
- Ability — a skill or capacity the subject holds: 泳げる ("can swim"), 話せる ("can speak").
- Possibility — the circumstances allow it, regardless of skill: この水は飲める ("this water is drinkable"), 明日なら会える ("if it's tomorrow, we can meet").
私、犬かきしかできないけど、一応泳げるよ。
watashi, inukaki shika dekinai kedo, ichiō oyogeru yo
I can only doggy-paddle, but I can swim, at least.
この水、そのまま飲めるのかな。
kono mizu, sonomama nomeru no kana
I wonder if you can just drink this water as is.
Two ways to say "can"
Japanese offers two routes to "can," and they overlap heavily:
- The native potential form — conjugate the verb: 読む → 読める, 行く → 行ける.
- する-verbs become できる, the suppletive potential of する: 運転する ("drive") → 運転できる ("can drive"). できる is also a standalone verb meaning "can do / be possible," and it pairs with nouns: 料理ができる ("can cook").
There is also the fuller, more formal frame 〜ことができる (泳ぐことができる), which packages any dictionary-form verb into "is able to." It is covered on its own 〜ことができる page. In everyday speech the one-word potential (泳げる) is far more common; the ことができる version sounds more careful or written.
兄は車の運転ができるけど、私はまだ免許を持っていない。
ani wa kuruma no unten ga dekiru kedo, watashi wa mada menkyo o motte inai
My older brother can drive, but I don't have my license yet.
The potential verb is itself an ichidan verb
Here is the fact that makes the whole system tidy: every potential form ends in -eる or -られる, so it conjugates exactly like an ichidan (ru-)verb — like 食べる. You never re-derive anything; you just clip the ichidan endings onto the potential stem.
| Form | 泳げる (can swim) | 話せる (can speak) |
|---|---|---|
| Dictionary | 泳げる | 話せる |
| Polite (masu) | 泳げます | 話せます |
| Negative | 泳げない | 話せない |
| Past | 泳げた | 話せた |
| Past negative | 泳げなかった | 話せなかった |
| te-form | 泳げて | 話せて |
昨日は忙しくて、昼ご飯も食べられなかった。
kinō wa isogashikute, hirugohan mo taberarenakatta
I was so busy yesterday I couldn't even eat lunch.
予約なしでも入れますか。
yoyaku nashi demo hairemasu ka
Can we get in without a reservation?
The deep point: the potential is stative
Competing explanations tell you how to form the potential and stop there. The insight that ties this whole subgroup together is that the potential is semantically stative — it describes a standing state (an ability, a possibility), not an action that happens at a moment. 泳げる doesn't describe an act of swimming; it describes the condition of being a person who can swim.
Two concrete consequences fall out of this stativity:
1. The object usually takes が, not を. Because "can eat bread" is closer to "bread is edible-to-me" than to "I act on bread," the thing eaten behaves like the subject of an adjective of ability and re-marks with が: パンが食べられる. This is not a quirk to memorize case by case — it flows directly from the form being stative. The full treatment, with the cases where を survives, is on the potential + が page.
この字、小さすぎて読めない。
kono ji, chīsasugite yomenai
The print is too small — I can't read it.
一人で行けるから、迎えに来なくて大丈夫だよ。
hitori de ikeru kara, mukae ni konakute daijōbu da yo
I can get there on my own, so you don't need to come pick me up.
2. It pairs naturally with 〜ようになる ("come to be able to"), because acquiring an ability is a change into a state.
最近やっと、早く起きられるようになった。
saikin yatto, hayaku okirareru yō ni natta
Lately I've finally become able to get up early.
A caution: 見える and 聞こえる are not the regular potential
A handful of perception verbs carry a separate, older "spontaneous potential" that means something presents itself to the senses on its own: 見える (mieru, "be visible / come into view") and 聞こえる (kikoeru, "be audible"). These are not the regular potentials of 見る and 聞く. The regular potentials — 見られる ("able to watch," e.g. a program you chose to see) and 聞ける ("able to listen") — describe an ability you exercise. Keep the two apart:
ここから富士山が見えるよ。
koko kara fujisan ga mieru yo
You can see Mt. Fuji from here (it's within view).
この映画、来週やっと見られる。
kono eiga, raishū yatto mirareru
I'll finally be able to watch this movie next week.
The first is spontaneous (the mountain simply is visible); the second is an ability you'll get to exercise. English blurs both into "can see," which is exactly why learners overuse 見られる where 見える is meant.
Common mistakes
❌ 私は泳ぐできる。
watashi wa oyogu dekiru
Incorrect — できる cannot be tacked onto a plain verb like English 'can.' Use the potential 泳げる, or 泳ぐことができる.
✅ 私は泳げる。
watashi wa oyogeru
I can swim.
The potential is a conjugation, not a separate word placed beside the verb. This is the number-one transfer error: English speakers reach for a standalone "can."
❌ 漢字が読めるない。
kanji ga yomeru nai
Incorrect — the potential itself is an ichidan verb, so its negative is 読めない.
✅ 漢字が読めない。
kanji ga yomenai
I can't read the kanji.
❌ 私は日本語を話せる。
watashi wa nihongo o hanaseru
Heard, but not the textbook default — a potential's object usually re-marks to が.
✅ 私は日本語が話せる。
watashi wa nihongo ga hanaseru
I can speak Japanese.
Keeping を is a real, understandable slip because English never re-marks the object. が is the safe default; see potential + が for when を is genuinely fine.
❌ この水は飲めるできる。
kono mizu wa nomeru dekiru
Incorrect — 飲める is already the potential; don't stack できる on top of it.
✅ この水は飲める。
kono mizu wa nomeru
This water is drinkable.
Key takeaways
- The potential form (可能形) conjugates the verb into "can / is able to" — Japanese changes the verb; English adds a modal.
- It covers both ability (泳げる) and circumstantial possibility (飲める, 会える).
- Every potential form is itself an ichidan verb — conjugate 泳げる like 食べる (泳げない, 泳げた, 泳げて).
- The potential is stative, which is exactly why its object leans to が and why it pairs with 〜ようになる.
- Keep the spontaneous perceptions 見える／聞こえる separate from the true potentials 見られる／聞ける.
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Start learning Japanese→Related Topics
- Potential Formation by Verb ClassN4 — How to build the potential form class by class — られる for ru-verbs, the -eる shift for u-verbs, and the suppletive できる / 来られる irregulars.
- Potential + が for the ObjectN4 — Why the object of a potential verb usually re-marks from を to が, and the conditions under which を survives.
- 〜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.