Modal Verbs : Abilities : Can-Could-Be able to

Modal verbs Part 2                     

You can learn Part1 Modal Verbs:General rules here.

To express  the ability we can use can-could-be able to.

 

 

 

The differences in the meaning of can and to be able to

Can  means  to have the ability or means to do something or it is used for saying what is possible.
To be able to is used for saying that it is possible for someone to do something,
where adj. able means  intelligent or good at doing something

Grammar forms 

As we have learnt , can has forms for the present (can) and  the past (could) and it has no form for the future . That's why we have to use its equivalent to be able to .

But at the same time to be able to  can be used in the Present,Past and Future as a usual phrase:

am/is/are able to (present)
was/were able to (past)
will be able to  (future)

Can  & be able to express the  ability to do something in present:
Nick can play football well.
Nick is able to play football well.

In the  past we can use could or to be able to. What is the difference?

We normaly use could with verbs see, hear, smell, taste, feel, understand ,guess, remember:
 He could see them well.
I could understand him.

Could and was / were able to (past form of  to be able to) can be used with no difference  for meaning ability in the past (repeted past action)

Ann could / was able to recite poems wonderful when she was a little girl!

But we must use be able to to express the ability  to do a single past action. We use  was/were able to to show that someone had an ability to do something in a particular time in the past.

They were able to complete the project on time !

Can / be able to in  negations and questions

In negations we can use be able to and could with no difference

He couldn't / wasn't able to  take part in this competition.

To make negations and questions with can/could we use this modal verbs
Can he dance well? He can't dance well.
Could they work together? They couldn't work together.

 To make negations and questions with to be able to we should use the correct forms of to be as an auxiliary verb. 

She was able to meet me yesterday.
She wasn't able to meet me yesterday.
Was she able to meet you yesterday?

We were able to attend her class last week.
We weren't able to attend her class last week.
Were you able to attend her class last week?

They will be able to  decorate the room for her birthday party.
They won't (will not) be able to  decorate the room for her birthday party.
Will they be able to  decorate the room for her birthday party.