can / be able to

Many books say the future tense of "can" is "will be able to". But "can" has at least three basic meanings:
C1, ability;
C2, epistemic can(possibility);
C3, permission.

Which meaning of the three the future tense can be applied to? For example,
S1,He can do the homework tomorrow.
In this sentence,I think "can" has the meaning of C3,but not C1 & C2.

So my question is, Could C1 & C2 have future tense (about a specific occasion)?
S2, He can be here tomorrow.
S3, He can finish the job tomorrow.
Do S2,S3 only mean "be allowed to"? Could S2 be epistemic and S3 be about ability?
(Maybe my examples (S2,S3) don't help me make myself understood well.)

Or simply, how should I understand the future tense of "can" is "will be able to"?

Many thanks in advance.

Let's keep this simple, Mengxin. Simplicity is usually the best way to go.

All these modal auxiliaries (can, may, might, should, ought to, must) and the semi-modal have to are used for the present or the future.

Could is used for the present when it means possibility.

Now, as for the sentence He can do the homework tomorrow, without context it's not just isolated to the meaning you've given, permission. It can also mean ability or opportunity.

As for the phrase be able to, we need this phrase to avoid two problems in the language. Read on and you'll see what I mean.*

"Why is it that English has this expression that is synonymous with can/could as long as the meaning is ability? Here are a couple of ungrammatical sentences ...

1. For that job at the United Nations, he needs to can speak at least three languages.

2. Canning speak four languages, he had no trouble getting that job at the UN.

Yes, we know these are really bizarre sentences! And that's just the point.

The corrections should be "he needs to be able to speak ..." for Sentence 1 and "Being able to speak ..." for Sentence 2.

In order for us to avoid such bizarre problems, we use be able to instead of can after prepositions and when an -ing form is required."

There you have it, Mengxin. Nice and concise. I hope this clarifies these points for you.

*Richard Firsten with Patricia Killian. The ELT Grammar Book: A Teacher-Friendly Reference Guide. Alta Book Center Publishers. Burlingame, CA. 2002

quote:

Now, as for the sentence He can do the homework tomorrow, without context it's not just isolated to the meaning you've given, permission. It can also mean ability or opportunity.

Thank you for your time,Richard.

It's easy to understand that "can" may mean "opportunity" here.

The following are about "ability":
As for "He can do the homework tomorrow" being correct, is it because of the word "tomorrow" itself? I forgot it has the meaning similar to "in the future".
I think "He can do the homework on Tuesday(Suppose today is Monday" is incorrect, am I right ? {I feel myself somewhat foolish now.}?

This message has been edited. Last edited by: Mengxin2009,

No, my friend. Assuming today is Monday, saying He can do the homework on Tuesday is perfectly fine.

We have an expression in English: "Don't make a mountain out of a mole hill." It means, don't make something complicated when it's really something simple.

Can, as I've said, represents the present or the future, depending on the context. It's that simple, okay?