According to the Oxford Grammar Course (Intermediate) book by Swan & Walter, we normally use can if we are deciding now what to do in the future. In other cases, we use will be able to.

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I need some help with the questions number 8, 10 and 11 in the first exercise of the page:

  • 8 I'm free at the weekend, so the kids __[can]__ come round.

  • 10 We're busy this week, but we __[can]__ repair it by next Thursday.

  • 11 I __[can]__ pay on Saturday – I promise.

I put can, as indicated here.

My reasons for all three:

  • 8) I think can is correct because the speaker is deciding to allow the kids to come round in the weekend though he is busy.

  • 10) I think can is correct because the speaker is deciding when exactly what to do the next Thursday.

  • 11) I think can is correct because the speaker is deciding (and consequently promising) what to do on Saturday.

But the answer key says these three sentences should have will be able to.

I really hope that there is someone here who has a deep knowledge of grammar and can explain to me why we can't use can in these three questions. Why do we have to use will be able to?

  • As a native speaker, my opinion is that you could use can with all of them, and I would think for (8) and (10), can would be the preferred verb. Commented Jul 7, 2018 at 0:54
  • @PeterShor Thank you. And what if you just wanna solve an exercise from a textbook? I mean what do you say if you wanna ignore real-life and just answer those 12questions and get the max score(12/12)? What will be your answer to #8,#10#,#11? Note that please, the author just saying we can use 'can', it's not necessary. So tell me please as a native speaker among those questions which ones satisfy the needed bolded condition (Deciding Now) to be able to use "CAN" too? I'm just wanna sure the answer key (even according to what the authors are saying) is wrong.
    – S Ped
    Commented Jul 7, 2018 at 5:13
  • @S Ped: I don't speak "textbook English", so I can't answer that question. Commented Jul 7, 2018 at 11:46
  • I think the textbook has a different idea of what "deciding now" means than native English speakers. In (8) and (10), the speakers are making plans, and for me that qualifies as "deciding now". In fact, if they're trying to decide on the time of a meeting, a native English speaker might say "I can't make next Thursday—I'll be in Paris." The textbook presumably thinks that the fact that the plane tickets have already been bought means that the speaker isn't deciding "now", and needs to use "won't be able to" (which I would use only if the meeting time has already been set). Commented Jul 7, 2018 at 13:35
  • @PeterShor I looked up the topic and didn't found any grammar reference book covering it. It exclusively belongs to Oxford Grammar Course intermediate and Advanced. Probably it would be interesting to see what does the Advanced book present? Imgur : i.imgur.com/geEA3bI.png. Any help or just they're repeating the same word from the first book?
    – S Ped
    Commented Jul 7, 2018 at 16:08

1 Answer 1


I think the rule the book describes is very subtle, and not obeyed rigidly by many native speakers. Both "can" and "will be able to" would probably be considered acceptable by most people.

But to explain the answer the book gives, these sentences are making predictions about something being possible, not making promises or describing decisions.

8) The subject of the clause is "the kids". The speaker can't make promises on their behalf, just predictions about their ability. You'd use "can" if it were something like "so I can take the kids".

10) To make a promise about something happening at a specific time, you'd normally use "will" all by itself. This sentence is making a prediction that they'd be less busy the following week, and they'll be able to finish the work then.

11) Again, a promise would be expressed with "will". The sentence is a prediction about the speaker's ability to pay, not a decision to pay.

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