can have done...is not used in English, only the negative... can't have done, is used He can't have been there yesterday........past impossibility......He can't have done that! He couldn't have been there yesterday.......past impossibility ( -can't have been- is a little stronger) *He couldn't be there yesterday.................negative past ability He could have been sick...........past possibility but did not happen He could be sick.........................present possibility Дополнительная информация: What's the difference. They knew it could be very dangerous......past possibility viewed from earlier in the past They knew it can be very dangerous.........present possiblity viewed from the past Дополнительная информация: *I could go to the store.....past ability (or present possibility ) I can go to the store.......present possibility/ability Also You could ask your doctor...........suggestion You could have asked your doctor.......past suggestion.

I think "can have done" is wrong. "Can have been doing" is better. (I guess, not necessary right - just my opinion) eg: If it isn't for you who is disturbing me right now, I can have been doing my homework. "Could do" is used to express conditional possibility or ability. Eg: You could do it if you tried. "Could have done" is used to express conditional possibility or ability that most probably didn't happen. Eg: You could have done all your homework if you didn't went out last night.

Yes, "He can't have been there yesterday" is incorrect. "Have been" points to a time in the past. So the "can" verb needs to agree = "couldn't have". Could vs. could have = The word "could" indicates an ability. Adding "have" to it indicates an ability in the past. I could go to the store. = I have the ability to go to the store. I can go to the store. He could be sick = It is possible he is sick. Or he has the ability to be sick. I could have gone to the store. = (notice "go" has to change to "gone" because the sentence becomes past tense with "have".) I had the ability to go to the store. This sentence also indicates that I did not go to the store, even though I had the ability. I couldn't go to the store = I wasn't able to go to the store. I couldn't have gone to the store = I wasn't able to go to the store. Even if I wanted to, I didn't go to the store. Hope this helps!