Modal Verbs of Probability

Perfect English Grammar


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Click here for all the exercises about modal verbs.

We can use these modal verbs (also called modals of deduction, speculation or certainty) when we want to make a guess about something. We choose the verb depending on how sure we are.

1: Talking about the present:

must / might / could / may / can't + infinitive

For example:

I am waiting for Julie with another friend, David.
I ask: 'Where is Julie?'
David guesses:

Notice that the opposite of 'must' is 'can't in this case.

Will / won't

We use will and won't when we are very sure:

Should / shouldn't

Should and shouldn't are used to make an assumption about what is probably true, if everything is as we expect: This use of should isn't usually used for negative events. Instead, it's a better idea to use will:

Can

Can is used for something that is generally possible, something we know sometimes happens: Can is not used to talk about specific possibilities:

2: Using modal verbs to talk about the past:

must / might / could / may / can't + have + past participle

(Click here to review how to make the past participle) For example:

You: Where was Julie last night?
David:

Will / won't + have + past participle

Will and won't / will not + have + past participle are used for past certainty (compare with present use of 'will' above):

Should + have + past participle

Should + have + past participle can be used to make an assumption about something that has probably happened, if everything is as we expect (compare with present use of 'should' above):

Could

We can use could + infinitive to talk about a general possibility in the past (compare with the use of 'can' above): This is not used to talk about specific possibilites in the past (instead we use could + have + past participle): Click here for modal verbs exercises