Modal Verbs of Probability


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