1. MODALS
Modal verbs are used to talk about ability, obligation, necessity, and permission.
Also when speculating, expressing certainty and possibility.
Past modals are used to talk about regrets, criticisms, and to speculate or make deductions about a past action or situation.

2. Certainty MUST ….strong certainty
Eg: Carol must live close to the school because she´s never late.
CAN´T …..strong certainty that something isn´t
Eg: It can´t be just a problem with my computer – none of the computers in the office are working.

3. We use must have, can´t have, couldn´t have, etc
We use must have, can´t have, couldn´t have, etc. with the past participle to talk about certainty in the past.
Eg: I can´t have lost the essays.
They were on my desk this morning.

4. Possibility CAN ….general possibilities or general truths.
Eg: This PC can crash without warning.
Taking out a loan can be risky.
MAY, MIGHT, WOULD, COULD …..speculate that something is possible.
Eg: There´s a message on the phone.
It may/might/could be from Jim.
What do you think has happened?
They may/might/could have missed the train.

5. When we speculate about something happening in the future, use MAY or MIGHT.
Eg. We may go this month or next month, I´m not sure.
It might be sunny when we´re in Manchester next week.
CAN and COULD also suggest that someone has the ability to do something.
Eg: Tom can speak German and English.
Use MAY HAVE, COULD HAVE, etc. with the past participle to talk about possibility in the past.
Eg: When I ring, there´s no reply.
They might have gone out.

6. PAST MODALS We form past modals using
a modal verb + have + past participle.
We normally use past modals to:
talk about regrets and criticisms about past actions or situations
speculate or make deductions about a past action or situation

7. Regrets and criticisms
SHOULD/SHOULDN´T HAVE + PAST PARTICIPLE …
to talk about past actions/situations we regret.
Eg: I really should have told my manager about the customer´s complaint.
I should have studied for the test.
We shouldn´t have come late.
Also to make criticisms of past actions/situations.
Eg: You shouldn´t have drunk so much beer.
She should have prepared for the exam.

8. OUGHT TO HAVE + PAST PARTICIPLE can be used instead of should/shouldn´t have + past participle to express regrets and criticisms.
Eg: We ought to have studied more.
WOULD and COULD can also be used for regrets and criticisms.
Eg: I would have prepared a better presentation.
We could have started the preparations
for the trip sooner.

9. Speculation and deduction
We use MUST HAVE + PAST PARTICIPLE when we feel very certain about a situation in the past.
Eg: Life 100 years ago must have been very difficult.
Sally must have worked hard to get such good
results in the examinations.
We use CAN´T/COULDN´T HAVE + PAST PARTICIPLE
when we feel very certain that a past situation was not the case.
Eg: I didn´t receive the bill. You can´t have sent it.
The inventors of the motor car couldn´t have known
the impact it would have on our environment.

10. When we speculate without certainty about
past events, we use
MAY/MIGHT/COULD + HAVE + PAST PARTICIPLE .
Eg: This coffee might have come from Central America.
The documents haven´t arrived. They could have
got lost in the post.
I´ll come to the presentation, but I think I may
have seen it already.

11. Past modals are closely related to the 3rd conditional
and I wish…/ If only…
Eg: If it hadn´t rained, more people would have come.
If the meeting had finished on time, she might
have cought her train.
I wish I lived in France.
I wish you wouldn´t keep ringing me.
If only I had studied for the test.
If only I hadn´t left my phone at home.

12. Obligation: HAVE TO / DON´T HAVE TO NEED TO WILL HAVE TO BE OBLIGED TO
Some more modals to express that
you must / have to do something:
HAVE TO / DON´T HAVE TO
NEED TO
WILL HAVE TO
BE OBLIGED TO
BE COMPELLED TO
* be careful with MUST and MUSTN´T
and HAVE TO / DON´T HAVE TO.

13. OTHER:
SHALL / SHOULD
HAD BETTER
OUGHT TO
BE DUE TO
BE BOUND TO