[General] can't have done/seen etc. versus couldn't have done/seen etc.

[JarekSteliga]

Do these two phrases mean two different things?

 

[5jj]

Context, as usual, is vital if we are to discuss the meanings of expresions.

 

[david11]

Not a teacher.

I haven't seen the phrase Can't have done.

 

[5jj]

I haven't seen the phrase Can't have done.

There are 158 COCA citations for 'can't have' + third form.

 

[david11]

There are 158 COCA citations for 'can't have' + third form.

I have searched(before posting my earlier reply) it but found only one.Corpus of Contemporary American English (COCA)

 

[david11]

.Corpus of Contemporary American English (COCA)

I gave the link to show that I have only one example but the link doesn't take us to page I saw.

 

[JarekSteliga]

Context, as usual, is vital if we are to discuss the meanings of expresions.

Again a fragment of a test which you not so long were not particularly fond of.

Complete the sentece using the word in bold. Use two to five words.

I'm sure Fred didn't steal the money. (have)

The answer provided by the author of this test is: Fred can't have stolen the money.

My question is if "Fred couldn't have stolen the money" is also acceptable.

 

[5jj]

Again a fragment of a test which you not so long were not particularly fond of.

"Fred can't have stolen the money" has roughly the idea of "It is logically improbable that Fred stole the money".
"Fred couldn't have stolen the money" is closer to the idea of "It was not possible for Fred to steal the money".

"Fred can't have..." is therefore closer to the idea of "I am sure Fred didn't..."

 

[JarekSteliga]

"Fred can't have stolen the money" has roughly the idea of "It is logically improbable that Fred stole the money".
"Fred couldn't have stolen the money" is closer to the idea of "It was not possible for Fred to steal the money".

"Fred can't have..." is therefore closer to the idea of "I am sure Fred didn't..."

Thank you.

Just to make sure I got it right.

'I am sure Fred didn't steal the money' matches 'Fred can't have stolen the money' (it is my strong conviction based on evidence, my experience etc.)

while

'Fred didn't steal the money' matches 'Fred couldn't have stolen the money' (the facts leave no room for speculation)

Would you notice/make a mental note if you heard someone mismatch the above?