蜜芽传媒

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Learning English - The Flatmates

Language Point

Archive Language Point 65
Modals - past possibilities, certainties and deductions

Common modals include: must, should, might, may, can, could, will, would. Modals affect the meaning of sentences. For example, some of them can be used to show possibility or probability.

I meet my boss at ten o'clock every day.
(a statement of fact)

I might see my boss tonight.
(the modal 'might' expresses a probability or possibility)

John can't see his boss tonight.
(the modal 'can't' means that it is not possible for John to see his boss tonight)

Grammar note:
With a present or future reference, the modal is followed by a base verb (the infinitive form of the main verb, without 'to').

I might see my boss tonight.
He could be in London.
She may arrive late.

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.
(This means you are certain it is the postman)

That might be the postman.
(You are not certain, but it is possible/probable)

That may be the postman.
(You are not certain, but it is possible/probable)

That could be the postman
(You are not certain, but it is possible/probable)

That can't be the postman.
(You are certain that it is NOT 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.

Past certainty
I must have left it in the last shop. I don't remember putting it in my pocket. (This means you are certain about something that happened in the past)

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)

Past possibility/probability
Someone might have stolen it.
Somebody may have taken it.
I could have dropped it.

Grammar note:
When modals are used to talk about past events, the modal is followed by the perfect infinitive, without 'to'.

The perfect infinitive is made with 'have' + the past participle of the main verb. Here are some examples of modal verbs followed by perfect infinitives:

must have left
might have stolen
may have taken
could have dropped

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'.