1. Modals and semi-modals

2. Modals and semi-modals
Can, may, must…
They are the same for all persons.
You must pay attention.
They don’t need an auxiliary verb for questions and negatives:
You shouldn’t swim when it’s windy.
Should I stay with you?
Two modal verbs can’t be used in the same phrase:
I will can play again next month (*).
Be able to, have to
They aren’t the same for all persons.
You have to pay attention / She has to pay attention.
They may need an auxiliary for questions and negatives:
You don’t have to say you’re sorry.
Do we have to speak in English?
They’re used when the modals can’t be used.
I will be able to play again next month.

3. SIMPLE MODALS Must / have to Obligation I must go to the hospital
Logical deduction (only must)
The film must be very good. Everybody likes it.
Can’t
Logical deduction
This person can’t be Michael. He’s too short.
Don’t have to
Lack of obligation
You don’t have to say you love me.
Mustn’t / can’t
Prohibition
We mustn’t smoke at school.
We can’t skip classes.
Can (past, could) / be able to
Ability
She can swim very fast.
I couldn’t concentrate yesterday.
Next year, I will be able to speak three languages.
Should / ought to
Advice
You should listen to your teachers.
May / might
Possibility
It may rain this afternoon. It’s very cloudy.
Can / could / may
permission
Can I come in, please?
Shall
Offering (used only in questions and with 1st persons)
Shall we continue?
Shall I give you my phone number?

4. PERFECT MODALS PERFECT MODALS: MODAL + HAVE + PAST PARTICIPLE
Should have
Criticism about a past action
You should have made a bigger effort.
You shouldn’t have used the present simple so often.
Must have
Logical deduction about something in the past
It must have been love, but it’s over now.
You must have worked very hard. I can see you’re so tired!
Could have
Ability to have done something which wasn’t done.
You could have written some more.
Couldn’t have
Disbelief
You couldn’t have finished so quickly. It’s impossible!
Needn’t have
An unnecessary past action
You needn’t have brought that bottle of wine. We have got plenty of it here.
Might / may have
Guessing about a possibility in the past
She might have forgotten to do her homework.
Would have
Past conditional: you wanted to do something, but you couldn’t
I would have gone to her party, but I wasn’t invited.