1. ABILITY
 

We use can to describe an ability and cannot or can’t to describe a lack of ability in the present:

She can speak Spanish but she can’t speak Italian.

If the present ability is surprising or involves overcoming some difficulty, we can also use is/are able to:

Despite his handicap he is able to drive a car.

To emphasise the difficulty or to suggest a great effort (in the present, past or future) we use manage to. In more formal English we can also use succeed in + -ing form:

Do you think she’ll manage to get a visa?

The army succeeded in defeating their enemy.
 

To describe a future ability we use will be able to:

Will I be able to speak fluently by the end of the course?
 

We also use be able to where can/could is grammatically impossible, for example:

I haven’t been able to drive since I dislocated my wrist. (with the perfect aspect)

We love being able to talk the local language. (with -ing forms and infinitives)


We use could to describe the possession of an ability in the past:

Mozart could play the piano at the age of five.
 

To describe the successful use of an ability on a specific occasion we do not use could, but rather,  was/were able to:

Mike's car broke down but fortunately he was able to repair it.
 

But we can use could in questions, and in sentences with limiting adverbs such as only or hardly:

‘Could you fix the computer yourself?’ ‘No, I could only back up the key files.’

She was so exhausted she could hardly speak.
 

We use couldn’t or was/were not able to to describe a lack of ability or success:

Mozart couldn’t speak French.

Despite being a mechanic, Mike couldn’t fix his car when it broke down yesterday.
 

2. POSSIBILITY, DEDUCTION AND SPECULATION
 

3. ARRANGMENTS, SUGGESTIONS, OFFERS
 

4. ASKING FOR AND GIVING/REFUSING PERMISSION
 

5. OBLIGATION AND NECESSITY
 

6. PROHIBITION AND CRITICISM
 

7. ABSENCE OF OBLIGATION OR NECESSITY
 

8. RECOMMENDATION AND ADVICE
 

9. LOGICAL DEDUCTION AND PROBABILITY
 

10. WILLINGNESS AND REFUSAL