LESSON NOTES · レッスンノート

N4Grammar, one piece at a time · Sep 12, 2026

ことができる vs the potential form: two ways to say "I can" in Japanese

Japanese has two ways to say "I can do it": the potential form (はなせます) and ことができます (はなすことができます). They mean the same thing, but they are not interchangeable — and one of them quietly changes your particle.

Textbooks usually teach these a chapter apart, so learners end up with one of them and never find out the other exists. Then they meet a sign or a form that uses the one they skipped. Both are worth owning, and the choice between them is mostly about register, with one grammatical trap hiding underneath.

The basics

What does ことができる literally mean?

Break it apart and there is no word for "can" in it at all:

  • こと — a nominalizer: "the act of", "the thing of"
  • — marks that act as the subject
  • できる — to be possible, to be doable

So およぐことができます is literally "the act of swimming is possible." It describes an ability as a fact about the world, which is exactly why it reads as formal and slightly detached — it is talking about the action rather than about you.

わたし日本語にほんごはなすことができます。 — I can speak Japanese. (polite, formal or written register) ここで写真しゃしんることができます。 — You can take photos here. (polite, the register signs and notices use)

How do you build it?

Dictionary form + ことができる. Nothing conjugates except できる at the end, which is the easiest verb pattern in the language to attach.

はなす → はなことができるはなことができます べる → べることができるべることができます する → することができる

Because the main verb never changes, this pattern is a genuine safety net: if you have not drilled the potential form yet, you can still express every "I can" sentence you need with a dictionary form you already know.

And the potential form?

The potential form conjugates the verb itself, and it is what people actually say.

Group Rule Examples
Group 1 (godan, う-verbs) final う-sound → え-sound + る はなす → はなせる / む → める / およぐ → およげる / く → ける
Group 2 (ichidan, る-verbs) drop る, add られる べる → べられる / る → られる
Group 3 (irregular) memorize both する → できる / る → られる

Note that する becomes できる — which is the same できる sitting at the end of ことができる. The two patterns are cousins, not rivals.

わたし日本語にほんごはなせます。 — I can speak Japanese. (polite, the everyday version) からいものがべられません。 — I can't eat spicy food. (polite negative, extremely common)

Beyond the basics

Which one should you actually use?

The potential form in speech, ことができる in writing and in formal or emphatic moments. That is the whole rule, and it holds up about ninety percent of the time.

If you say はなすことができます to a friend, you sound like you are reading from a brochure. If you write はなせます on an official application, it is not wrong, but ことができます looks more finished. The longer form also adds weight when you want it: わたしにもできることがあります lands harder than a bare potential form because it draws attention to the act itself.

英語えいご説明せつめいすることができますか。 — Would it be possible to explain in English? (polite, formal — a request to staff or an office) 英語えいご説明せつめいできますか。 — Can you explain in English? (polite, everyday — same meaning, lighter)

The particle changes — this is the real trap

With the potential form, the object usually takes が instead of を. With ことができる, it stays を.

日本語にほんごはなせます。 — I can speak Japanese. (potential form takes が) 日本語にほんごはなすことができます。 — I can speak Japanese. (ことができる keeps を)

Both を and が are acceptable with the potential form, and you will hear 日本語にほんごはなせます from native speakers. But が is the textbook-correct and more natural choice, and it is the one graders and forms expect. Getting this backwards — 日本語にほんごがをはなすことができます, or dropping が where it belongs — is the single most common error I see on this grammar point.

The reason is structural: in ことができる, the subject slot is already taken by こと, so the object has nowhere to go but を. In the potential form, the ability itself is the predicate, and the thing you are able to do slides into the subject slot.

What happens in casual speech?

The potential form shrinks, and ichidan verbs lose their ら.

からいものべれない。 — I can't eat spicy stuff. (casual — べられない with ら dropped) 明日あしたれる? — Can you come tomorrow? (casual — られる → れる)

This is called ら言葉ことば ("ra-dropping"), and it is everywhere in speech and anime while still being marked as incorrect in writing and in exams. Know it so you can hear it; do not put it in an email. ことができる, by contrast, never contracts — another reason it belongs to the written register. Which situations license the casual version is the usual question, covered in casual vs. polite Japanese.

How do the negative and past work?

Only the ending changes, in both patterns, because できる and られる are both ichidan verbs.

Potential form ことができる
Present はなせます はなすことができます
Negative はなせません はなすことができません
Past はなせました はなすことができました
Past negative はなせませんでした はなすことができませんでした

去年きょねん日本にほんくことができませんでした。 — I wasn't able to go to Japan last year. (polite past negative, formal) チケットがれなかった。 — I couldn't get a ticket. (casual past negative)

What about 日本語にほんごができる, with no verb at all?

That is a third pattern, and it is the shortest of the three: noun + が + できる, where the verb is implied.

かれ中国語ちゅうごくごができます。 — He can speak Chinese. (polite — "speak" is understood) 運転うんてんができません。 — I can't drive. (polite — noun + できる)

This works with nouns that describe an activity — 日本語にほんご, 運転うんてん, 料理りょうり, テニス. It is the most natural way to talk about skills, and it saves you a conjugation entirely.

Common mistakes

  • Using を with the potential form by default. 日本語にほんごはなせます is tolerated; 日本語にほんごはなせます is what you want.
  • Conjugating the verb inside ことができる. It is はなすことができます, never はなせることができます — that stacks two potentials.
  • Using ことができる with a friend. Grammatically fine, socially stiff. Use the potential form.
  • Writing ら言葉ことば. べれる is fine to say and wrong to write. In anything graded or official, べられる.
  • Forgetting that する becomes できる. 勉強べんきょうすることができる is correct, but 勉強べんきょうできる is what people say — and it is not a shortcut, it is the standard form.
  • Treating られる as only potential. べられる also means "to be eaten" (passive). Context separates them, which is precisely why ことができる exists as an unambiguous alternative.

Practice

Each answer is hidden — work out your version first, then open it. If you get the particle right on every one of these, this grammar point is done.

1. Put む into the potential form, polite.

Show answer

めます — Group 1 verb, so the final む becomes め and you add る: む → める → めます.

2. Fill in the particle: わたし日本語にほんご( )はなせます。

Show answer

わたし日本語にほんごはなせます。The potential form pulls the object into the subject slot. を is heard in speech but が is the form to use.

3. Fill in the particle: わたし日本語にほんご( )はなすことができます。

Show answer

わたし日本語にほんごはなすことができます。Here こと already occupies the subject slot, so the object keeps を. This is the pair to question 2 — the particle is the only thing that moves.

4. Rewrite およげます using ことができます.

Show answer

およぐことができます — go back to the dictionary form (およぐ), then attach ことができます. Do not start from the potential form: およげることができます stacks two potentials and is wrong.

5. Something is wrong here: 明日あしたれることができますか。

Show answer

明日あしたることができますか。 — two errors stacked. れる is already potential (and is ら言葉ことば besides), so ことができる on top is doubled. The everyday spoken version would simply be 明日あしたられますか。

6. Make it negative, polite: からいものをべる。

Show answer

からいものがべられません。 — potential form べられる, negative べられない, polite べられません. Note the particle moved to が. The ことができる version is からいものをべることができません。

7. Say "I couldn't get a ticket" in casual past negative.

Show answer

チケットがれなかった。る → れる → れない → れなかった. Only the ending carries the tense; the potential part stays put.

8. Which of these belongs on a public notice: ここで写真しゃしんれます/ここで写真しゃしんることができます?

Show answer

ここで写真しゃしんることができます — signs, notices, and forms use the long written form. れます is correct Japanese but reads as conversational for a public notice.

9. Rewrite 運転うんてんすることができません in the shortest natural way.

Show answer

運転うんてんができません。運転うんてん is an activity noun, so noun + が + できる works and no verb conjugation is needed at all. 運転うんてんできません is equally natural.

10. べられる has two meanings. What are they, and how would you avoid the ambiguity?

Show answer

"can eat" (potential) and "to be eaten" (passive). Context normally settles it, but when it genuinely matters you use べることができる, which can only mean ability. That is the one job the long form does better than the short one.

FAQ

Is ことができる ever wrong where the potential form works? Not grammatically, but it can be socially wrong — it sounds stiff in casual conversation. The reverse is also true: the potential form on a formal application looks unfinished rather than incorrect.

Which should a beginner learn first? ことができる, because nothing conjugates — you attach it to a dictionary form you already know. Then learn the potential form properly, because it is what you will hear.

Is べれる really wrong? It is standard in speech and marked as incorrect in writing. Treat it the way you would treat "gonna" in English: recognize it, say it, don't write it.

Why does する become できる instead of しられる? Historical irregularity, like most of Group 3. The upside is that it gives you できる, which then powers both noun + できる and the ことができる pattern — one irregular form doing three jobs.

Can I use ことができる with adjectives? No. こと attaches to verbs here. For "I can be quiet," you need a verb — しずかにすることができます — not the adjective on its own.

Does 〜られる ever attach to a Group 1 verb? Not for the potential. はなされる is passive or honorific, not "can speak." Group 1 verbs form the potential with the え-sound: はなせる. Mixing these up is a good reason to keep your te-form and verb groups straight.

Vocabulary from this article

Tap the block to select all of it, then copy. In Anki: File → Import, note type Basic, separator Tab — the first column becomes the front, the second the back.

話す	はなす — to speak
読む	よむ — to read
泳ぐ	およぐ — to swim
食べる	たべる — to eat
行く	いく — to go
来る	くる — to come
見る	みる — to see, to watch
取る	とる — to take, to get (a ticket)
撮る	とる — to take (a photo)
説明する	せつめいする — to explain
運転	うんてん — driving
料理	りょうり — cooking, a dish
写真	しゃしん — photograph
辛い	からい — spicy
去年	きょねん — last year
明日	あした — tomorrow
英語	えいご — English (language)
日本語	にほんご — Japanese (language)
中国語	ちゅうごくご — Chinese (language)
できる	できる — to be able, to be possible
こと	こと — thing, act (nominalizer)

I'm Yuuki, a Japanese teacher based in Tokyo. I've taught on italki as a Top 1% teacher and watched over 1,500 anime, and the particle swap in questions 2 and 3 above is the thing I correct most often on this grammar point — students learn both patterns and then use one pattern's particle with the other's structure.

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Sources: the author's own lessons and standard reference grammars.

More drills like the ones above, plus a timed JLPT-style mock test: Practice · N4

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