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
- must + infinitive
- might / might not + infinitive
- could / could not + infinitive
- may / may not + infinitive
- can't + infinitive
I am waiting for Julie with another friend, David.
I ask: 'Where is Julie?'
- She must be on the bus. (I'm fairly sure this is a good guess)
- She might come soon. (maybe)
- She could be lost. (maybe)
- She may be in the wrong room. (maybe)
- She can't be at home. (I'm fairly sure this isn't true)
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:
- She'll be at work now.
Should / shouldn'tShould and shouldn't are used to make an assumption about what is probably true, if everything is as we expect:
- They should be there by now.
- It shouldn't take long to drive here.
- The underground will be very busy now (not: 'should be').
CanCan is used for something that is generally possible, something we know sometimes happens:
- Prices can be high in London.
- He could be on the bus (not: 'can be').
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)
- must have + past participle
- might / might not have + past participle
- could / couldn't have + past participle
- may / may not have + past participle
- can't have + past participle
You: Where was Julie last night?
- She must have forgotten about our date.
- She might have worked late.
- She could have taken the wrong bus.
- She may have felt ill.
- She can't have stayed at home.
Will / won't + have + past participleWill and won't / will not + have + past participle are used for past certainty (compare with present use of 'will' above):
- The parcel will have arrived before now.
Should + have + past participleShould + 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):
- The train should have left by now
CouldWe can use could + infinitive to talk about a general possibility in the past (compare with the use of 'can' above):
- Prices could be high in the sixteenth century.
- He could have been working late (not: 'could be'. As this is a specific possiblity, 'could be' is present tense)