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What’s the difference between “can” and “will be able to” in this sentence in the context? I want to distinguish between them so please don’t tell me they mean the same.

A: We’ve got lost. What should we do?

B: Jack grew up here. If we give him some information, he’ll be able to/can give us directions.

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    You have asked several questions about this, and there really isn't any definite distinction between the two. Perhaps he will be able to carries more of a suggestion that the information will be necessary to enable him to help. "If we tell him where we want to get to, he'll be able to give us directions."
    – Kate Bunting
    Commented Jul 21 at 16:26
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    If they are the same, how would you have us modulate our answers to account for the devoutness of your desire that they be different?
    – Paul Tanenbaum
    Commented Jul 21 at 17:25
  • I don't agree with either of the answers so far. They are trying to be helpful and find differences for you because of the way you asked your question. But in my view there simply is no difference. You owe it to them and us to explain why you think there is a difference. Then we can/will be able to help.
    – Peter Kirkpatrick
    Commented Jul 21 at 18:52
  • @PeterKirkpatrick: So you don't think my point about I'll do the washing-up and you will be able sweep the floor being structurally the same (but idiomatically / semantically invalid) is relevant? Given we don't know why giving Jack information affects getting directions from him in the OP's example, I don't see how you can casually dismiss one of the biggest differences between possible ways of using can and will be able to.
    – FumbleFingers
    Commented Jul 22 at 16:09
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    @FumbleFingers, you've given a good answer and I take your point. Fwiw, you will note the use of either answer in my comment. I only remember two answers when I wrote it; I don't think yours was available on my screen at the time.
    – Peter Kirkpatrick
    Commented Jul 22 at 21:53

3 Answers 3

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I'm sure most people would say that in the cited context, can and will be able to are semantically equivalent...

Jack grew up here. If we give him some information...
1: ...he’ll be able to give us directions.
2: ...he can give us directions.

But the nuance of difference can be seen by comparing the above to...

We need to clear up this untidy mess! I'll do the washing-up and...
3: ...you can sweep the floor.
4: ...?you will be able sweep the floor. <== Doesn't work!

In OP's cited context, the "condition" (giving Jack some information) is a very "weak" precondition. It wouldn't really be any different if it was phrased as...

Jack grew up here. We'll just give him some information and...
5: ...he’ll be able to give us directions.
6: ...he can give us directions.

...where it still makes no difference to #6 (but not #5) if we change give him some information to ask him nicely.

In short, to be able to (with was / is / will be = past / present / future) almost always carries the sense of having the ability to do something.

But can - which has no "future" form (and could isn't always "past" was able to) - sometimes signifies little more than "assignment" of value / role (Let X be 7, and Y can be 9). It doesn't necessarily have any implications for ability as such.

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  • I think "If+will be able to" is like this: He will gain the ability to give us directions if we give him some information. "If+can" is like this: His helping us will be possible if we give him some information.
    – Chien Te Lu
    Commented Jul 22 at 3:24
  • Yes, I think that's a good way of looking at it (for some contexts; the distinction doesn't always apply). Arguably it could even reduce to His helping us will follow as a consequence... It's not clear from the question exactly what information Jack would "need" We don't know if Jack is with the speaker, or needs to be told where they are or where they want to go, in order to give directions. For all we know, Jack is with them, but won't cooperate unless they tell him some secret that has nothing to do with the problem of being lost.
    – FumbleFingers
    Commented Jul 22 at 10:13
  • Or the information is something Jack needs to check something. He already has the ability to check but he needs some data to do so, and the speaker suggests that they should give him the information to get the directions. In this sense, “can” works fine as Jack’s lack or possession of the ability is not emphasized. It’s just a suggestion made by the speaker. On the other hand, “will be able to” is more like Jack has already told them that he can’t do anything without the information needs. He will only gain the ability to help them if they give him the information. Do you agree? @FumbleFingers
    – Chien Te Lu
    Commented Jul 22 at 14:53
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    I think you're overthinking this one. You wrote the original sentence, so presumably you know what you wanted it to mean. Native speakers wouldn't be likely to say If we give Jack some information [he might do something] anyway, so I can't really "agree" with you about what your text might mean. You asked about the difference between can and will be able to, and you insist you want to know a difference even though in practice for your specific example there probably isn't a difference. I've told you a "possible, theoretical" difference that might apply. End of story.
    – FumbleFingers
    Commented Jul 22 at 16:03
  • I am not saying you are wrong, and I agree the difference is subtle but indeed exists. Maybe "will be able to" has a stronger connection between the if clause and the ability to perform the actions than "can." As you have mentioned, "If you ask him nicely, he can help you out" is different from "If you ask him nicely, he'll be able to help you out" as the first one means that asking nicely makes his help available (it might have little to do with his ability) while the second means that he gains the ability to help if you ask him nicely (which is weird though) @FumbleFingers
    – Chien Te Lu
    Commented Jul 23 at 6:17
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The key is that right now, Jack cannot give us directions. After all, he does not know what our destination is. But if we give him enough information, then this will change. The fact that "can" is defective means that we need to replace "can" with "to be able to" if we want to express the future.

That being said, one would probably still prefer to use "can" in the situation -- after all, it is just the lack of our detailed question that's preventing Jack from helping us.

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In the context of this sentence:

"Can" refers that it is possible that Jack can give them directions. They are confident that since Jack grew up there, he can easily answer them.

Example: He can swim. Means we are sure that he can swim.

But, if "will be able to" is used they are not sure that they will get some information from Jack. They are predicting that Jack will be able to give information but they were not certain to get information from him.

Example: He will be able to catch Train. Means we are predicting that he will be able to catch Train, but not sure.

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  • "He will be able to catch a/the train". There is no suggestion of uncertainty unless the statement is qualified - "If there isn't too much traffic on the road to the station he will be able to catch the train".
    – Kate Bunting
    Commented Jul 21 at 16:25
  • I think "If+will be able to" is like this: He will gain the ability to give us directions if we give him some information. "If+can" is like this: His helping us will be possible if we give him some information. "can" is more like we should do something so that Jack's help will be available to us. It's not that he doesn't have the ability to help right now.
    – Chien Te Lu
    Commented Jul 22 at 3:25

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