We use can't have or couldn't have to say that a past event was impossible: We use can't or cannot to say that something is impossible: (= People often got lost in that town.) could and could have (= It was sometimes very cold there in winter.) We use could to make general statements about the past: Where are they? They could have got lost. We use may have, might have or could have to make guesses about the past: Notice the difference in meaning between can and may/ might/ could:

He may/ might/ could be(NOT can) in his office. We do not use can to talk about specific events:ī: I'm not sure. (= People often get lost in this town.) Be careful!

(= It is sometimes very cold here in winter.) We use can to make general statements about what is possible:

We use may, might and could to say that something is possible, but not certain: