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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 (話はなせます) and ことができます (話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"
  • が — marks that act as the subject
  • できる — to be possible, to be doable

So 泳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.

私わたしは日本語にほんごを話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を撮とることができます。 — 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.

話はなす → 話はなすことができる → 話はなすことができます 食たべる → 食たべることができる → 食た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 話はなす → 話はなせる / 読よむ → 読よめる / 泳およぐ → 泳およげる / 行いく → 行いける
Group 2 (ichidan, る-verbs) drop る, add られる 食たべる → 食たべられる / 見みる → 見みられる
Group 3 (irregular) memorize both する → できる / 来くる → 来こられる

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.

私わたしは日本語にほんごが話はなせます。 — I can speak Japanese. (polite, the everyday version) 辛からいものが食たべられません。 — 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 話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 話はなせます 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: 私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.

英語えいごで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) 英語えいごで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.

日本語にほんごが話はなせます。 — I can speak Japanese. (potential form takes が) 日本語にほんごを話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 日本語にほんごを話はなせます 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話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.

辛からいもの食たべれない。 — I can't eat spicy stuff. (casual — 食たべられない with ら dropped) 明日あした、来これる? — Can you come tomorrow? (casual — 来こられる → 来これる)

This is called ら抜ぬき言葉ことば ("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 話はなせます 話はなすことができます
Negative 話はなせません 話はなすことができません
Past 話はなせました 話はなすことができました
Past negative 話はなせませんでした 話はなすことができませんでした

去年きょねんは日本にほんに行い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) チケットが取とれなかった。 — 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.

彼かれは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.

飲のみません or 飲のめません — "don't" and "can't" are one letter apart

English uses "I don't drink" for both a choice and an inability, and lets tone sort it out. Japanese puts the difference in the verb, and the two forms are separated by a single vowel.

お酒さけは飲のみません。 — I don't drink. (polite; a choice or a habit — you decline) お酒さけは飲のめません。 — I can't drink. (polite; an inability — your body, your medication, your religion)

The same split runs through every verb you own:

肉にくを食たべません。 — I don't eat meat. (a choice — vegetarian by decision) 肉にくが食たべられません。 — I can't eat meat. (an inability — an allergy, or you simply cannot get it down)

Which one you choose carries real social weight. At a Japanese dinner table 飲のめません ends the conversation kindly, because nobody presses someone who physically cannot. 飲のみません invites a "just one?" because a choice can be changed. If you want the refusal to stick without explaining yourself, the potential form is the one to reach for.

Notice the particle moving in the second pair: 肉にくを食たべません but 肉にくが食たべられません. That is the same particle shift covered above, and it is the most reliable sign of which form a speaker used when the vowel goes by quickly.

Common mistakes

  • Using を with the potential form by default. 日本語にほんごを話はなせます is tolerated; 日本語にほんごが話はなせます is what you want.
  • Conjugating the verb inside ことができる. It is 話はなすことができます, never 話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 ら抜ぬき言葉ことば. 食たべれる is fine to say and wrong to write. In anything graded or official, 食たべられる.
  • 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. 食たべられる 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 読よむ into the potential form, polite.

Show answer

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

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

Show answer

が — 私わたしは日本語にほんごが話はなせます。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: 私わたしは日本語にほんご( )話はなすことができます。

Show answer

を — 私わたしは日本語にほんごを話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 泳およげます using ことができます.

Show answer

泳およぐことができます — go back to the dictionary form (泳およぐ), then attach ことができます. Do not start from the potential form: 泳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、来これることができますか。

Show answer

明日あした、来くることができますか。 — two errors stacked. 来これる is already potential (and is ら抜ぬき言葉ことば besides), so ことができる on top is doubled. The everyday spoken version would simply be 明日あした、来こられますか。

6. Make it negative, polite: 辛からいものを食たべる。

Show answer

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

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

Show answer

チケットが取とれなかった。 — 取とる → 取とれる → 取とれない → 取とれなかった. 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を撮とれます/ここで写真しゃしんを撮とることができます?

Show answer

ここで写真しゃしんを撮とることができます — signs, notices, and forms use the long written form. 撮とれます 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. 食たべられる 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 食たべることができる, 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 食たべれる 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 — 静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. 話はなされる is passive or honorific, not "can speak." Group 1 verbs form the potential with the え-sound: 話はなせる. 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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