koto-ga-dekiru-vs-koto-ga-aru

You’ve been studying Japanese for a while now, and you feel confident with こと. Then you see two sentences side by side:

📌 日本語を話すことができる。 — I can speak Japanese.
📌 日本に行ったことがある。 — I have been to Japan before.

Same こと. Same が. Same ある/できる ending. But wildly different meanings. If you’ve ever written the wrong one and wondered why your Japanese friend looked confused, you’re in exactly the right place. This guide breaks down ことができる (ability and possibility) vs ことがある (past experience) once and for all.

ことができる — Ability and Possibility

ことができる expresses that someone has the ability to do something, or that something is possible. It is the formal equivalent of the potential verb form, and it attaches to the dictionary form (plain non-past form) of a verb.

Formation: Verb (dictionary form) + ことができる

Notice that the verb before こと is always in its dictionary form — the base form you find in a dictionary: 話す, 弾く, 撮る, 読む, 解く. This is the key signal that we are talking about ability, not experience.

ことができる also appears in formal or written contexts to express possibility — that something is permitted or achievable, not just a personal ability:

📋 このチケットで新幹線に乗ることができます。
With this ticket, you can ride the Shinkansen. (= it is possible / permitted)

Yuka

So ことができる is like saying “I have the ability to…” or “It is possible to…”? That makes sense — the verb stays in its base form because you’re talking about a general skill, not something that already happened!

Rei

Exactly! Think of it as a present fact about what you can do. The ability exists right now, so you use the present-tense (dictionary) verb form. That’s your first clue for telling these two apart.

ことがある — Past Experience (“Have Ever Done”)

ことがある expresses that you have had the experience of doing something at some point in the past. In English, this is often translated as “have ever done” or “have done before.” It attaches to the た-form (past tense form) of a verb.

Formation: Verb (た-form) + ことがある

Formation note: The た-form is the plain past tense. For Group 1 (u-verbs): 飲む → 飲んだ, 書く → 書いた. For Group 2 (ru-verbs): 食べる → 食べた, 見る → 見た. For irregular verbs: する → した, くる → きた.

The た-form before こと is the essential signal: something happened in the past, and that past event is now a part of your life experience. You’re not talking about current ability — you’re talking about something you once did.

This pattern is extremely common in Japanese conversation when people share life experiences:

🗨️ スカイダイビングをしたことがある？
Have you ever gone skydiving?

🗨️ ない！怖そう！あなたは？
No! Sounds scary! What about you?

Yuka

Wait — I need to remember: ことがある uses the た-form, not the dictionary form. So if I want to say “I have eaten natto before,” I say 納豆を食べたことがある, not 納豆を食べることがある!

Rei

Perfect! 納豆を食べることがある would actually mean something different — it’s a less common usage that means “there are times when I eat natto” (occasional occurrence). That’s an advanced nuance. For beginners, just remember: past experience = た-form + ことがある.

The Confusion Trap — Why Learners Mix Them Up

Both patterns use こと + が + ある/できる, so at first glance they look almost identical. Here are the most common mistakes English speakers make:

Mistake 1: Using the Wrong Verb Form

This is the most frequent error. The verb form before こと tells you everything:

Mistake 2: Confusing できる and ある

Learners sometimes swap the ending too:

Mistake 3: The “Sometimes” Confusion

There is an advanced usage of dictionary-form verb + ことがある (without た) that means “there are times when…” or “sometimes…”:

📌 仕事で遅く帰ることがある。
There are times when I come home late from work. / I sometimes come home late from work.

This is different from the experiential ことがある! Context and the verb form (dictionary vs. た) separate them. For N4–N3 learners, focus first on the experiential usage (た-form + ことがある). The “sometimes” usage appears more in writing and formal speech.

Negative Forms: ことができない vs ことがない

The negatives are just as important as the affirmatives — and the same verb-form rule applies.

ことができない — Cannot Do (No Ability)

Formation: Verb (dictionary form) + ことができない

たことがない — Have Never Done (No Experience)

Formation: Verb (た-form) + ことがない

Key difference in the negatives:

Yuka

So if I want to say “I have never driven a car,” I need to use the た-form: 車を運転したことがない. But if I want to say “I cannot drive a car,” I use the dictionary form: 車を運転することができない. The difference is huge!

Rei

You’ve got it! And notice: “I have never driven” doesn’t say anything about whether you can or not. Maybe you never had the chance but you could learn! “I cannot drive” is a statement about ability right now. These are genuinely different ideas in Japanese.

Simpler Alternatives: できる vs たことがある

Both patterns have shorter, more conversational alternatives. In everyday speech, especially casual conversation, Japanese speakers often drop the こと entirely.

ことができる → できる (Potential verb form)

Most verbs have a potential form that means “can do.” These are shorter and sound more natural in casual speech:

Both forms are grammatically correct. Use ことができる in formal writing, official contexts, or when you want to emphasize the possibility aspect. Use the potential form in everyday conversation.

ことがある → たことがある (already shortened!)

For the experiential pattern, the “full” form and the casual form are essentially the same. However, you may hear native speakers drop ことが entirely in very casual speech:

📌 Formal: 日本に行ったことがあります。
📌 Casual: 日本に行ったことある。
📌 Very casual: 日本に行ったことある？ (question form, dropping the period)

In casual speech, が is often dropped (ことある instead of ことがある). The meaning stays the same. Just be aware of this when listening to native speakers.

When to use the formal ことができる instead of the potential form

Some verbs do not have a standard potential form, or using ことができる sounds more natural in certain contexts:

Side-by-Side Sentence Comparison

The clearest way to understand the difference is to see both patterns used with the same verb. Let’s compare:

Study the verb forms carefully. The pattern is consistent:

• 話す (dictionary) + ことができる = ability to speak
• 話した (た-form) + ことがある = experience of having spoken

This one rule — dictionary form for ability, た-form for experience — unlocks both patterns.

Decision Flowchart

Not sure which pattern to use? Follow this flowchart:

START: What do you want to express?
          |
          |
    +-----------+----------+
    |                      |
    v                      v
Are you talking        Are you talking
about ABILITY?         about EXPERIENCE?
(Can you do it?)       (Have you done it?)
    |                      |
    v                      v
Use DICTIONARY         Use TA-FORM
form + ことができる     + ことがある
    |                      |
    v                      v
話すことができる       話したことがある
"I can speak"         "I have spoken before"
    |                      |
    v                      v
Negative?              Negative?
ことができない         たことがない
"I cannot speak"      "I have never spoken"
    |                      |
    v                      v
Simpler option?        Simpler option?
Use potential form     Drop が in casual speech:
話せる (casual)        話したことある

Quick Quiz

Test your understanding! Choose the correct form for each sentence. Answers are below.

Question 1: I can read hiragana.
a) ひらがなを読んだことができる
b) ひらがなを読むことができる
c) ひらがなを読むことがある

Question 2: I have never eaten uni (sea urchin).
a) うにを食べることができない
b) うにを食べることがない
c) うにを食べたことがない

Question 3: Have you ever been to Hokkaido?
a) 北海道に行くことがありますか？
b) 北海道に行ったことがありますか？
c) 北海道に行くことができますか？

Question 4: She cannot play the guitar.
a) 彼女はギターを弾いたことができない
b) 彼女はギターを弾くことができない
c) 彼女はギターを弾いたことがない

Question 5: I have tried Japanese sake before.
a) 日本酒を飲むことができる
b) 日本酒を飲んだことがある
c) 日本酒を飲むことがある

Question 6: You cannot smoke in this restaurant.
a) このレストランでタバコを吸ったことがない
b) このレストランでタバコを吸うことがない
c) このレストランでタバコを吸うことができません

———

Answers:

• Q1: b) ひらがなを読むことができる — Ability uses the dictionary form (読む), not た-form (読んだ).
• Q2: c) うにを食べたことがない — “Have never eaten” = た-form + ことがない.
• Q3: b) 北海道に行ったことがありますか？ — Asking about past experience requires た-form.
• Q4: b) 彼女はギターを弾くことができない — “Cannot play” = dictionary form + ことができない. Option c) means “has never played.”
• Q5: b) 日本酒を飲んだことがある — “Have tried before” = た-form + ことがある.
• Q6: c) タバコを吸うことができません — Prohibition (cannot do) = dictionary form + ことができない/できません.

How did you do? If you got 5 or 6 correct, you’ve mastered the core distinction! If you got fewer, review the verb form before こと — that’s always the key.

Which question tripped you up? Share in the comments below — knowing where learners get confused helps us write better explanations for everyone!

Keep Learning

Now that you can tell ことができる from ことがある, these related grammar guides will help you keep building confidence:

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