Elephants CAN BE very dangerous. a general fact A hundred years ago, flu COULD BE very dangerous. a fact about the past Your keys COULD BE in your other jacket a guess about the present They're 30 minutes late. They COULD HAVE GOT lost. a guess about the past This bill CAN'T BE correct. It's too much. impossibility: present You CAN'T/COULDN'T HAVE SEEN me yesterday. I was at home all day. impossibility: past They arrived over an hour late. They COULD HAVE PHONED us! a past event that was possible but didn't happen https://339efcb25eb75e967b0d-ff8eeadd950d51fd1fc939dca75b3973.ssl.cf1.rackcdn.com/assets_green.swf