If Dad comes home early tomorrow night, he can help you with that.

[MichaelLu2000]

I made up these sentences so there's no source.

A: I have trouble doing my math homework.
B1: If Dad comes home early tomorrow night, he can help you with that.
B2: If Dad comes home early tomorrow, he’ll be able to help you with that.

I think the main difference is that B1 sounds like B is suggesting Dad as an available option for A to consider asking for help from while B2 sounds more straightforward: Dad will have the ability to help A given that he comes home early tomorrow.

I am not sure if I've distinguish between them correctly, but I know there's a difference. Please share with me your opinions.

 

[tedmc]

I'd say B is more natural. B1 is general while B2 is specific.

 

[teechar]

while B2 sounds more straightforward: Dad will have the ability to help

I agree.

am not sure if I've distinguished between them correctly,

Because "can" expresses ability or possibility, using the standard ("will"+Vbase) "will be able to" is preferred here.

Note that "can" does work in some conditional-1 contexts. For example:

If you promise to be polite, you can come to the party.

 

[MichaelLu2000]

I agree.

Because "can" expresses ability or possibility, using the standard ("will"+Vbase) "will be able to" is preferred here.

Note that "can" does work in some conditional-1 contexts. For example:

If you promise to be polite, you can come to the party.

Does B1 sound more suggestive?

 

[teechar]

No. I don't think so.

 

[jutfrank]

I think it's a poor example if you want it to be a suggestion. The context you've written sounds like you're talking about the father's ability.

Let me change it for you to sound more like a suggestion:

Well, if he gets home early tomorrow, perhaps your dad can help.

 

[MichaelLu2000]

I think it's a poor example if you want it to be a suggestion. The context you've written sounds like you're talking about the father's ability.

Let me change it for you to sound more like a suggestion:

Well, if he gets home early tomorrow, perhaps your dad can help.

Does “can” sound more suggestive than “will be able to” in this case?

 

[jutfrank]

Does “can” sound more suggestive than “will be able to” in this case?

In my example? Yes. It doesn't just 'sound' that way—that's what it means.

 

[MichaelLu2000]

In my example? Yes. It doesn't just 'sound' that way—that's what it means.

Sorry, what I want to ask is whether “can” sounds more like making a suggestion than “will be able to” in your dad example.

 

[jutfrank]

Yes, that's why I wrote it. The whole utterance is a suggestion.

 

[MichaelLu2000]

Yes, that's why I wrote it. The whole utterance is a suggestion.

I think when “can” means opportunities, it sounds more like making a suggestion than “will be able to”

Like this:

A: What should I do if I get in trouble?
B1: If there’s a policeman on the scene tomorrow night, he can help you out.
B2: If there’s a policeman on the scene tomorrow night, he’ll be able to help you out.

For this example, I think B1 is better for suggesting that you should ask a police officer to help you. B2 might sound like the policeman’s being there will give him the ability to help, which is weird because policemen’s being present doesn’t give them the strength or authority to help. They have the ability to help because they are police officers not because they are there.

 

[jutfrank]

Yes. As I've said before, 'be able to' has the word 'able' in it, so it always sounds like ability. It's not particularly good for suggestions, permission, requests, etc.

 

[MichaelLu2000]

Yes. As I've said before, 'be able to' has the word 'able' in it, so it always sounds like ability. It's not particularly good for suggestions, permission, requests, etc.

This is the shortest but the best answer.