When talking about possibilities in the past, You often use **"could have done".** >"She could have gone to the theatre with him."<br> "He couldn't have done such a thing!"<br> "I could have saved them."<br> "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."<br> "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."<br> "He can have told them all the secrets."<br> "I can have saved them."<br> "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."<br> "She can be nasty." Did **"can have done"** in affirmatives used to exist before?<br> Or is it still possible but only used in limited contexts?<br> If it is, when do you use the structure?<br> If it's not used at all, what do you think is the reasons?<br> Should I just think of it as an exception or an irregularity?<br><br> **※.** I've already read this link: http://ell.stackexchange.com/questions/7519/how-often-do-you-use-cant-have-done-structure<br> **※. One thing added:** I looked up **'can'** in *Oxford Advanced Learner's Dictionary of Current English*<br> *(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.<br> b. He's an hour late; he **can have been delayed** by bog, of course. Now I'm thinking **"can"** really used to express speculations about the past,<br> and the meaning was more or less the same as **"could"** or **"may".**<br> if the interesting affirmative **"can"** was still alive in some dialects, I'd love to know about them and to know<br> whether the choice between **'can'** or **'could'** might be a matter of lowering possibility in the dialects.