Can I use the helping verb can in the future? "I can travel to London tomorrow." Or I have to use able to? "I am able to travel to London tomorrow."

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    You can use 'can' for future events. I can visit you tomorrow. You can drive my car next Sunday. – Michael Harvey Nov 14 '19 at 11:55

'Can' is perfectly fine in this context, though it is often used in a 'reserved' manner, by which I mean that someone might well say "I can travel to London tomorrow, (but really don't want to.)"

'Can' is not a direct replacement for 'Able to' in all circumstances - it works fine in your example, but to borrow Michael H's example, "You can drive my car" does not mean the same thing as "You are able to drive my car"

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  • I'm not sure about that a 'reserved' manner. It seems to me the "reserved, cautious, tentative, provisional" sense is more naturally conveyed with the explicitly "non-Present" form I could travel to London tomorrow (but I'd rather not). – FumbleFingers Reinstate Monica Nov 14 '19 at 16:27
  • @FumbleFingers Yeah, 'Reserved' in its normal sense isn't the word I was scrabbling for, but still can't think of the right one! – Mike Brockington Nov 14 '19 at 16:32
  • In formal English, that second sense of "can", conveying permission rather than ability, is instead handled by "may". – Monty Harder Nov 14 '19 at 23:19
  • @MontyHarder: I'd say that usage is more "dated" than "formal". I asked the boss if I might leave work early isn't something you're likely to hear today (it's always ...if I could). – FumbleFingers Reinstate Monica Nov 15 '19 at 13:21

English doesn't really have a Future Tense anyway, but I would say that in I can go tomorrow, can is effectively Present Tense. You can see this at the syntactic level by noting that the "future" version of I can go is I will be able to go.

But it's also true at the semantic level, in that I can go tomorrow effectively means My current status is that I will be able to go tomorrow. That "present tense reference to future ability" may be more obvious if we also consider negating contexts...

[My mother's dementia is getting worse...]
1: ... I hope she will be able to recognise me next Christmas
2: ... I'm afraid she won't be able to recognise me next Christmas (won't = will not)
3: ... I hope she can recognise me next Christmas (QUESTIONABLE - see below)
4: ** I'm afraid she can't recognise me next Christmas (INVALID)

Most native speakers would accept the "Present as Future" usage in #3 - particularly if extended to ...can still recognise me (which more overtly references the passage of time between now and next Christmas).

But note that most native speakers would not accept #3 if we change I hope... to The doctor says... That's because my specific example refers to [future] ability. In a structurally / syntactically identical example where the meaning is more about [present / future] permission, there's no real difference between...

5: The doctor says I can go home tomorrow
6: The doctor says I will be able to go home tomorrow

Because it's both a "defective" verb (with an incomplete conjugation) and a "modal" (auxiliary verb expressing necessity or possibility), can is a difficult word to master in English. There's too much to cover in a single Answer here on ELL, but I'll just point out that in most contexts, the meanings of...

7: The doctor said I can go home tomorrow
8: The doctor said I could go home tomorrow

...are identical. But sometimes, #8 means ...might be able, not ...will be able or ...will be permitted.

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  • Thanks all for good information. I understand now it is right to say: – Sdg Nov 14 '19 at 21:10
  • Thanks so no difference between. I will be able to travel tomorrow And I can travel tomorrow. – Sdg Nov 14 '19 at 21:14
  • @Sdg: Normally there's also no difference with I am able to travel tomorrow. Mostly these are just stylistic choices, with no particular syntactic or semantic implications. – FumbleFingers Reinstate Monica Nov 15 '19 at 13:48

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