|Learning English - The Flatmates|
Modals - possibility, probability, guesses and deductions
Modals can be used to show possibility, probability, a guess or a deduction (a guess which is based on evidence).
For example, you are in your house and the doorbell rings (you can't see who is at the door). You say:
That must be the postman.
That might be the postman.
That may be the postman.
That could be the postman
That can't be the postman.
Must, might, may, could and can't are also used to talk about past probability and possibility, and to make guesses and deductions about things that happened in the past.
For example, after a shopping trip you go to the train station to return home. You can't find your wallet.
I can't have left it in the last shop. I remember putting it in my pocket. (This means you are certain about something that DIDN'T happen in the past)
must have left
Remember, if you don't use a modal, then you are giving a fact, for example: I left it in the shop.
Be careful: Modal verbs often have other different meanings. For example, 'could' can be used to show ability as well as possibility. Use the context to help you understand which meaning is being used. 'Can' is NOT normally used to talk about the past: use 'could'.