be able to VS can

[panicmonger]

Why I cannot say "I can speak....."?
Instead I have to use "will be able" in the sentence below.

I will be able to speak French at the end of this course.

Wholeheartedly grateful.

 

[nyota]

You can use can if you're deciding now what to do in the future,
e.g. I can see you tomorrow morning if you like.

But otherwise, you have to use will be able to. So will be able to functions as a future form of can,
e.g. One day I will be able to speak French/ I will be able to speak French at the end of this course.

 

[5jj]

Nyota is correct, panicmonger.

I'll just add, in case you didn't know, that we cannot use modals together.

I [STRIKE]will can[/STRIKE] speak French. I [STRIKE]may must[/STRIKE] go.

If we wish to express such ideas, we have to find alternative ways, such as:

I will be able to speak French.
It is possible that I will have to go.