Quote:
Originally Posted by Preslang  Does this construction exist in English ? , and what it means: can + have + past participle |
The construction exists in English, but I have to disagree with Riverkid about the implications. Modal verbs are different in many respects from other English verbs, but they still show tense. Modals exist in pairs (present/past):
wiil/would
can/could
shall/should
may/might
In order to understand that, you have to understand that a tense is a construction that is often related to time, but a specific tense can refer to a time other than what is named in that tense (past, future, etc.) and the past tense can be used for things other than past time, such as politeness or hypothetical situations.
The constructiuon you are referring to is "can have + past participle". We also have "could have + past participle". The first has a present tense modal and the second has a past tense modal. So let's look at the difference.
He can't have eaten all five pizzas by himself.
He couldn't have eaten all five pizzas by himself.
Both sentences express the speaker's disbelief with reference to the action.
They have almost identical meanings. The only difference is where the speaker places himself. The first sentence puts the speaker's disbelief in the prersent. (Even now) I can't believe that.... The second sentence is just a statement about the past, so it uses a past tense modal.
These examples don't say very much about tense because the meanings are too close. Let's look at another example of "can" versus "could".
Ten years ago, I could run a marathon; today I couldn't/can't.
In the first clause, "could" is obviously past tense. The time is clearly in the past (ten years ago). One cannot substitute "can" for "could", because the time is in the past.
The second clause is obviously in the present. Therefore, one can use either modal. The present tense "can't" is more concrete. It gives the impression that the speaker has tried and failed. One can also use "couldn't". The past tense form gives the impression of a hypothetical situation. The past tense of verbs is often used for that reason. The speaker may have chosen "couldn't" because he has a bad hip or has gained 50 pounds, either of which would be likely to interfere with a 26 mile run. In any case, modals give the reader/listener a window into the mind of the speaker. Modal verbs are extremely important and they do not need to be strippped of "tense" to accomplish their tasks.