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When talking about possibilities in the past, You often use "could have done".

"She could have gone to the theatre with him."
"He couldn't have done such a thing!"
"I could have saved them."
"You could have borrowed the car from him."

I understand "can have done" is used in negative and interrogative statements.

"She can't have eaten all the food."
"Can he have told them all the secrets?"

But I've not seen an affirmative sentence like,

"She can have gone to the theatre with him."
"He can have told them all the secrets."
"I can have saved them."
"You can have borrowed the car from him."

Why is it? As far as I know, "can" sometimes refers to possibilities as follows.

"It can be boiling hot in summer."
"She can be nasty."

Did "can have done" in affirmatives used to exist before?
Or is it still possible but only used in limited contexts?
If it is, when do you use the structure?
If it's not used at all, what do you think is the reasons?
Should I just think of it as an exception or an irregularity?

※. I've already read this link: How often do you use "can('t) have done" structure?
※. One thing added: I looked up 'can' in Oxford Advanced Learner's Dictionary of Current English
      (Third Edition, 1974, A.S. Hornby), and here are the examples:

a. One of the prisoners escaped yesterday; he can/could(=may) be anywhere by now.
b. He's an hour late; he can have been delayed by fog, of course.

Now I'm thinking "can" really used to express speculations about the past,
and the meaning was more or less the same as "could" or "may".
if the interesting affirmative "can" was still alive in some dialects, I'd love to know about them and to know
whether the choice between "can" or "could" might be a matter of lowering possibility in the dialects.

I really want to hear different opinions on this "can".

  • This has been asked on ELU. – Esoteric Screen Name Aug 8 '14 at 15:22
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    This is a good question. :) The other thread(s) doesn't have an answer for your question, as your question is asking for the reason why: "In its epistemic use can, . . . , is restricted to non-affirmative contexts." (CGEL page 180) -- I suspect this might have something to do with grammaticalization. Hopefully someone with the resources and time might be willing to answer your question. If they do, I'll be sure to read it. Good luck! – F.E. Aug 8 '14 at 17:12
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    "b. He's an hour late; he can have been delayed by bog, of course." -- not sure on this one. It could perhaps be non-standard in using the epistemic use of "can", or perhaps it might be standard usage by mainly using a different type of modality. – F.E. Aug 8 '14 at 18:04
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    Also "can have done" and "can have been" can be found, quite not rarely, in books published in the 21th century. – Damkerng T. Aug 8 '14 at 20:03
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    @DamkerngT., it's worth noting that "published" is not exactly synonymous with "written" - Dickens, Austen, Stoker, and Descartes were all around well before the 21st century, although my own attempts to answer this question have found examples of the "can have done" construct in academic linguistic research from the past decade (unfortunately, this use of "can" is not the subject of anything I have found yet). – Pockets Aug 8 '14 at 23:57
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What your referring to with "can have" in an affirmative statement, is correctly expressed with "may have:"

She may have gone to the theater with him. (I'm not sure)

I may have saved them. (We'll soon find out)

The other use of "can" refers to general tendencies, usually not in a specific situation. The opposite of this usage would logically be "never." In other words, the opposite of "She can be nasty" IS NOT "She cannot be nasty," but rather "She is never nasty."

  • Thanks. Would you check out two exmaples just added? – daemang Aug 8 '14 at 18:18
  • (a) is fine without have, however (b) sounds strange to me with "can." I personally would use "might" or "may" in this context. – CocoPop Aug 8 '14 at 20:19
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    @daemang "I can have saved them" could mean "I may have saved them" or the very different "I could have saved them". "can have" is not only ambiguous but sounds awful to a native speaker and should be avoided. – Jim Balter Aug 11 '14 at 7:17
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I am a native speaker of American English. I'm not a professional in the area of the English language.

My belief is that "can have" is not incorrect, but it is awkward to me, and to most American English speakers in my experience... "can" most commonly is used in a situation where there is a possibility of alternate outcomes. This implies a present or future tense. "could have" and similar "have" compounds imply the past tense and so "can have" is awkward at best. It strains the common usage of 'can' to make it describe a past or present tense, and if I heard someone say "can have" I would first wonder if this was some British English usage, and after that I would probably conclude that the speaker meant this "past or possibly present" tense sense that I described above. Most people would probably just be confused.

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