Can and "be able to" are both used to show abilities, talents, or strengths. They have the same meaning.
- I can swim.
- I am able to swim.
- She can speak English well.
- She is able to speak English well.
We can use "cannot" and "be not able to" to show that something or somebody does not have an ability or to show a weakness.
- People can't fly.
- People are not able to fly.
- I can't dance well.
- I am not able to dance well.
"Can" and "be able to" have the same meaning and can be used in the same way, but we usually them in different situations.
1. "Can" is much easier to say and use. So, almost all English speakers use "can" if possible.
- Can you ski?
- Can you come to my party?
- I can run fast.
- She can cook well.
- They can speak Russian.
2. "Can" is a modal. We cannot use two modals together. So, when we want to express "can" with another modal, then we have to use "be able to".
Here is a list of English modals.
So, we use "be able to" with these words because it is impossible to use "can" together with the other modals.
- I will not be able to come.
- She might be able to help us.
- They must be able to speak English to work here.
- We should be able to go in at 9.
- You should be able to use Excel if you work here.
- We may be able to finish today.
- We would be able to help you if you came here.
3. Since "could" is the past tense form of "can", we do not use "be able to" with "could". But we can use both to express abilities or possibilities in the past.
- I couldn't swim when I was young.
- I was not able to swim when I was young.
I could able to swim.
4. We also use "be able to" with the present perfect tense, but we cannot use "can" this way.
- She has been able to swim since she was 5.
- They have been able to help us a lot this week.
- She hasn't been able to come because of the bad weather.
Even though "can" and "be able to" have the same meaning, use "can" whenever possible. Use it to make simple sentences and questions about ability or possibility.
- Birds can fly, but I can't fly.
- She can't come to the party because she has to work.
We usually use "be able to" together with modals.
- I will be able to come.
- She might be able to lend us some money.
- We should be able to do it.
We also use "be able to" with the present perfect.
Understanding this lesson will help your English sound more natural. So, make sure you spend enough time studying this English lesson.
- I have been able to study quietly today because my brother is not in the house.
- She has been able to play the piano since she was 3 years old.