Most of the time can and be able to can be used interchangeably without causing any trouble in meaning. However, there are some slight differences that need to be pointed out.
Can is a modal verb, and it’s used to talk about general ability in the present tense. For example:
- I can speak English.
- I can ride a bike.
- She can drive.
In the sentences above, you could use ‘be able to‘ instead of ‘can‘, but ‘can‘ is more common among native speakers.
Using ‘be able to’
‘Be able to’ is not a modal auxiliary verb. It consists of three parts:
- The conjugated form of ‘to be‘
- the adverb ‘able‘
- and the infinitive ‘to‘
- I am able to learn complicated languages.
- I am able to handle situations which used to baffle me in the past.
- He is not able to lift that mountain.
You can see from the above example that if you want to create a negative sentence, just place ‘not‘ after ‘to be‘
Using ‘be able to’ for past and future abilities
You can also use ‘be able to’ to express abilities in the past and in the future.
For past abilities:
- I was able to learn languages.
- You were able to swim.
For future abilities:
- I will be able to swim.
- You will be able to help him soon.