Modal Verbs of Ability in English

Modal Verbs of Ability in English: Can, Could, and Be Able To

Modal verbs of ability in English include can, could, and be able to. Although they often seem similar, they are not always interchangeable. In this complete guide, you’ll learn the difference between can, could and was able to, with clear explanations, practical examples, and exam-focused tips for B2 First and C1 Advanced.

Let’s go step by step.

Can – Present Ability (and General Future)

We use can to talk about ability in the present.

Structure:

Subject + can + base verb

Examples:

• Ann can type very fast.
• I can swim.
• She can speak three languages.
• We can meet tomorrow.

Future Meaning with “Can”

We often use can for future arrangements when the situation is already possible.

• I can pay you next week.
• We can discuss it tomorrow.

This is natural and common in everyday English.

Be Able To – More Formal / Other Tenses

Be able to has the same basic meaning as can, but it is:

• slightly more formal
• necessary when we need other tenses

Why? Because can has only two forms:

• can (present)
• could (past)

If we need future perfect, present perfect, infinitive or gerund, we must use be able to.

Examples:

• I will be able to pay you next week.
• She has been able to solve the problem.
• I would like to be able to speak Japanese.
• Being able to work from home is convenient.

So think of be able to as the “complete” form that works in all tenses.

Could – Past Ability (General Ability)

We use could to talk about general ability in the past.

Structure:

Subject + could + base verb

Examples:

• She could read when she was four.
• He could play the violin at six.
• We could run very fast when we were younger.

This describes repeated or general ability — not a specific successful action.

Was/Were Able To – Specific Success in the Past

Here is where learners often make mistakes.

When we talk about a single successful action in the past, we usually use:

was/were able to

Example:

• The door was locked, but I was able to open it.
• We were able to catch the last train.
• She was able to pass the exam after months of study.

This suggests that it was difficult, it required effort and the action was successfully completed.

Important Contrast – Modal Verbs of Ability in English

❌ I could open the locked door.

(Usually incorrect if you mean one specific occasion.)

✅ I was able to open the locked door.

However…

Exception: Verbs of Perception

With verbs like see, hear, smell, feel and understand, we often use could even for single actions.

• I could hear someone crying.
• She could see the mountains from her window.
• I could smell something burning.

In these cases, could sounds completely natural.

Negative Forms

In negative sentences, couldn’t and wasn’t able to are both common — even for single actions.

• She couldn’t pass the test.
• She wasn’t able to pass the test.

Both are acceptable.

Questions

In questions, both forms are possible:

• Could you swim when you were five?
• Were you able to finish the report?
• Could you get to work every day last week?
• Were you able to speak to the manager?

There is often little difference in meaning.

Summary Table

Common Mistakes – Modal Verbs of Ability in English

❌ I could pass the exam yesterday.

(If you mean a specific exam result.)

✅ I was able to pass the exam yesterday.

❌ I can to swim.

✅ I can swim.

❌ I will can go.

✅ I will be able to go.

Final Thoughts

The key difference is this:

• Could = general ability in the past
• Was able to = specific successful action
• Can = present ability
• Be able to = all other forms

Once you understand that distinction, the system becomes much clearer.

And in exams, that clarity makes all the difference.

FAQ – Modal Verbs of Ability in English

What is the difference between could and was able to?

We use could for general past ability and was able to for a specific successful action in the past.

Can we use could for one specific past action?

Usually no — except with perception verbs like see, hear and smell.

When do we use be able to instead of can?

We use be able to in tenses where can is not possible, such as the future perfect or present perfect.

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Modal verbs of obligation