Where is my phone?
- PAST CERTAINTY(MUST HAVE + PARTICIPLE) :
I must have lost it !!!
- PAST POSSIBILITY (COULD HAVE + PARTICIPLE) :
- I might have left it at home.
- I could have left it on the bus. (Alternative action)
- REGRET OR CRITICISM ABOUT A PAST EVENT:
I shouldn't have been in such a hurry!