Is such construction correct? And if so, what's the difference in usage between "can+have+PP" and "could+have+PP"?

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Is such construction correct?

No. 'Can' only works in present simple. If you want to use it in pp you're going to have to put it back into the past, and one fnction of 'could' is as a past form of 'can' in the same way that 'would' can function as a past form of 'will'. Alternatively you could use a pp form of 'be able to' + infinitive:-
'I've been able to dance since I was ten'.
And if so, what's the difference in usage between "can+have+PP" and "could+have+PP"?

Only the second one works.
'I could have danced all night'
or a conditionally one:-
'I could have told you that if you'd asked me'.
DC
O czasie 2004-06-03 11:36, taki/taka jeden/jedna Django Cat wzia;/e;?(a) i napisa?(a) :
Only the second one works. 'I could have danced all night' or a conditionally one:- 'I could have told you that if you'd asked me'.

how about:
'If we keep travelling, we can have seen all the European capitals by the end of this year.'

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O czasie 2004-06-03 11:36, taki/taka jeden/jedna Django Cat wzia;/e;?(a) i napisa?(a) :

Only the second one works. 'I could have danced all night' or a conditionally one:- 'I could have told you that if you'd asked me'.

how about: 'If we keep travelling, we can have seen all the European capitals by the end of this year.'

No. 'Can' doesn't work in the future, either. You have to use 'be able to':-
'If we keep travelling, we will have been able to see all the European capitals by
the end of this year.'
Some people would describe this as the 'future perfect tense', but see Cyber Cypher's post under 'how many tenses...', which I agree with.

DC
O czasie 2004-06-03 11:36, taki/taka jeden/jedna Django Cat wzia;/e;?(a) i ... all the European capitals by the end of this year.'

No. 'Can' doesn't work in the future, either. You have to use 'be able to':- 'If we keep travelling, we ... describe this as the 'future perfect tense', but see Cyber Cypher's post under 'how many tenses...', which I agree with.

Wouldn't you in real life say "If we keep travelling, we could have seen..."?

Mike.
O czasie 2004-06-03 11:36, taki/taka jeden/jedna Django Cat wzia;/e;?(a) i ... all the European capitals by the end of this year.'

No. 'Can' doesn't work in the future, either. You have to use 'be able to':- 'If we keep travelling, we will have been able to see all the European capitals by the end of this year.'

I'd say 'If we keep traveling, we can see all the capitals...' To throw in a few more words, '...we'll be able to see all the capitals...' You have to throw in a lot of extra words to get to 'we will have been able to see...'
I would say that you can use 'can' with a past participle if it's negated: 'We can't have come that far. It's only been one hour.' Then an argumentative reply could be 'We can have come that far- we were doing ninety.'

john
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Is such construction correct?

No. 'Can' only works in present simple.

Not true.
John is competing in an eating contest most hot dogs in ten minutes. He deliberately paces himself to eat a maximum of three per minute; otherwise he gags. The starter fires the starting gun and wanders off behind the platform where the contest is being staged. An eating-contest fan encounters the starter and asks him how he thinks John is doing. Starter looks at watch and sees that give minutes have elapsed. "John can have eaten fifteen hot dogs by now."
Okay, it's a bit stilted. It's English. Have a gander at (search for "john can have"). This example was written by someone who appears to be a fully literate native speaker of English. See also .

Inverted into question form it's much more natural: "Can John have eaten fifteen hot dogs yet?" "Can we have arrived already?" Can anyone have asked this question before?" Try searching for "can john have."
There may be other ways possibly even better ways to frame these variuos sentences, but there's nothing wrong with them as is.

Bob Lieblich
Can I have finished already
No. 'Can' doesn't work in the future, either. You have to use 'be able to':-

I disagree I think the above, with "can" in the present, is fine.
'If we keep travelling, we will have been able to see all the European capitals by the end of this year.'

That's correct too, but it describes a possibility that will apply at the end of the trip, if the intention to keep traveling is carried out. The previous version describes a possibility that applies now, by establishing the intention to keep traveling.
"can have seen" 643
"will be able to have seen" 6
"can have done" 3,470
"will be able to have done" 7
"can have finished" 251
"will be able to have finished" 4
"can have accomplished" 67
"will be able to have accomplished" 0
"can have painted" 51
"will be able to have painted" 0
Note that while the relative google counts support my point, the absolute numbers are pretty low, suggesting that in practice people look for other ways to say things like this.
Wouldn't you in real life say "If we keep travelling, we could have seen..."?

I certainly wouldn't the sequence of tenses is wrong.
Mark Brader, Toronto > "It's easier to deal with 'opposite numbers' (Email Removed) > when you know you cannot trust them." Chess

My text in this article is in the public domain.
"can have seen" 643 "will be able to have seen" 6 "can have done" 3,470 "will be able to have done" 7

You really need to rake through these a bit to see if they really are being used in the way you suggest. Out of the first few pages of 'can have seen' hits, only one struck me as semi-valid. It was from a translation of a novel by a Swedish writer. Even here, 'could have seen' would have been fine, and certainly to my ears, a better choice.
"Can have done" is even problematic because it is a valid formation - "Do you know what repairs I can have(=get) done to my car".

Still, it's surprising common. I wonder if I'd notice if someone slipped such a formation into everyday speech. If I don't pay attention, by the end of the day I can have heard someone use it without even noticing.

Dylan
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