Ability: Can, Could & Be Able To

In English, the modals of ability — can, could, and be able to — are the 3 main tools for talking about what someone is able or unable to do. Each one fits different slots:

Can and could are quick and natural, but they are limited — they only have present and past forms. Be able to fills all the gaps where can and could cannot go: future tenses, present perfect, and after other modals or verbs. The key challenge is knowing which tool to reach for in each situation.

Note: "Can" is also used to talk about permission (e.g. Can I sit here?). This lesson focuses on ability only. For permission, see Permission: Can, Could & May.

Present Ability: Can & Can't

Use can + base verb to say what someone is able to do right now, and can't (cannot) for things they are unable to do.

Affirmative

Key point: Can is a modal verb — it never changes form. No -s, no -ing, no -ed.

• ✅ She can cook.
• ❌ She cans cook.

Negative

The full form is cannot (one word), and the contraction is can't. The negative is always can't or cannot — never "don't can" or "not can":

• ✅ I can't swim.
• ❌ I don't can swim.
• ❌ I not can swim.

Questions & Short Answers

Tip: Don't use contractions in positive short answers.

• ❌ Yes, I can't. → ✅ Yes, I can.

Can with Perception Verbs

With verbs of perception (see, hear, smell, taste, feel), English uses can where many other languages use the simple present tense:

• I can see the mountains from here. (not just "I see the mountains")
• Can you hear that noise?
• I can smell something burning.

This also applies to mental verbs like understand and remember:

• I can't understand what he's saying.
• I can remember her face clearly.

👉 Practice Can & Can't: Present Ability →

Past Ability: Could & Couldn't

Use could + base verb for general abilities you had in the past, and couldn't (could not) for things you were unable to do.

General Past Ability

"Could" describes what someone was generally able to do over a period of time — not just on one occasion:

• When I was a teenager, I could stay up all night without feeling tired.
• My grandfather could speak five languages when he was younger.
• In the 1990s, people couldn't use the internet easily. It was very slow.

Questions & Short Answers

Common Time Expressions with Could

These past time expressions signal that "could" is the right choice:

Don't confuse: "Could" also has other uses — polite requests (Could I borrow your pen?) and possibility (It could rain). When combined with a past time expression, "could" means past ability.

👉 Practice Could & Couldn't: Past Ability →

Be Able To: Beyond Can & Could

Can and could are limited — they only have present and past forms. For all other tenses and structures, use be able to.

Present: Am / Is / Are Able To

This has the same meaning as "can" but is less common in everyday speech:

• She is able to solve complex problems. (= She can solve...)
• Are you able to understand the instructions?
• He is able to fix almost anything around the house.

Past — Specific Achievements: Was / Were Able To

This is the most important rule in this lesson:

For one-time successes in the past — where someone actually managed to do something on a specific occasion — use was/were able to, not "could":

• After hours of work, he was able to fix the engine. ✅
• After hours of work, he could fix the engine. ❌

Why? "Could" means you had the general ability over a period. "Was able to" means you actually succeeded on that specific occasion.

Synonym: "Managed to" is an informal alternative to "was able to" for specific achievements:

• She managed to pass the exam. (= She was able to pass the exam.)

Exception — Perception verbs: With see, hear, smell, taste, feel, you can use "could" even for specific past moments:

• I could see the mountains clearly that morning. ✅
• I could hear someone singing in the next room. ✅

Future: Will Be Able To

Can has no future form. Use will be able to:

• She will be able to speak fluently by next year.
• I won't be able to attend the meeting tomorrow.
• Will you be able to come to the party on Saturday?

Present Perfect: Have / Has Been Able To

Use this for ability that started in the past and continues to now. Look for time markers like since, recently, yet, and for:

• She has been able to drive since she got her licence last month.
• I haven't been able to sleep well recently because of stress.
• They haven't been able to find a solution yet.
• He has been able to concentrate better since he started meditating.

Common mistake: Don't use "could" with "since" — it requires present perfect:

• ❌ She could swim since she was five.
• ✅ She has been able to swim since she was five.

After Other Verbs & Modals

When ability follows another verb or modal, you must use be able to — you cannot combine two modals:

👉 Practice Be Able To: All Tenses →

Can vs Could vs Be Able To — How to Choose

Quick Decision Table

The Key Rule: Could ≠ Was Able To

This is the distinction that causes the most mistakes:

More examples showing the contrast:

• I couldn't play tennis before, but after taking lessons I was able to beat my brother last week.
  • "couldn't" = general past inability ✅ / "was able to" = specific one-time success ✅
• The police were able to catch the thief after a long chase. (They actually caught him.)
• Despite the heavy rain, they were able to finish the match. (They actually finished.)

Two Exceptions

1. Negatives — both forms work:

For past inability, you can use either form with no difference in meaning:

• I couldn't find the restaurant. ✅
• I wasn't able to find the restaurant. ✅

2. Perception verbs — "could" is fine for specific past moments:

With see, hear, smell, taste, and feel, you can use "could" even for a specific occasion:

• I could see the mountains clearly that morning. ✅
• I could hear someone singing in the next room. ✅

👉 Practice Can vs Could vs Be Able To →

Common Mistakes to Avoid

Quick Summary

Ask yourself two questions to choose the right form:

Question 1: What time frame?

Question 2 (past only): General ability or specific achievement?

Key rules to remember:

• Can never changes: no -s (cans), no -ing, no -ed
• Negative = can't or cannot (never "don't can")
• Questions = Can + subject + base verb? (no do/does)
• Two modals cannot go together → use be able to (will can, should can)
• Since requires present perfect → has been able to (not could)

Practice Tips

1. Describe your abilities: Write five things you can do and five things you can't do now. Then write five things you could do as a child but can't do anymore.
2. Tell a success story: Describe a time you achieved something difficult — practise using "was able to" and "managed to" instead of "could".
3. Future plans: Talk about skills you will be able to develop — "After this course, I will be able to..."
4. Spot the difference: When talking about the past, always ask yourself: "Is this a general ability (could) or a one-time success (was able to)?"
5. Watch for double modals: If you need to combine ability with another modal (might, should, will) or verb (want to, hope to), always use "be able to".

Practice All Exercises

Ready to put everything together? Start with the Mixed Ability Expressions set for a comprehensive review:

👉 Practice Mixed Ability Expressions →