Английская грамматика: модальные глаголы

5. It was expected in the past but didn't happen (should + have + past participle).
This expresses the idea that the subject did not fulfill their obligation in the past or did not act responsibly.
You should have given your boss the report yesterday when he asked for it.


6. Not fulfilling an obligation (should + be + verb -ing).
This expresses the idea that the subject is not fulfilling their obligation or is not acting sensibly.
7. Sometimes should is replaced by ought to without a change in meaning. Note that ought to sounds more formal and is used less frequently.
They ought to stop doing that. (= They should stop doing that)
Shouldn't

We use shouldn't to advise not to do something, usually because it is bad or wrong to do.

You shouldn't throw your litter onto the street.

5. Modal verbs. May and might

Теория:
Study the information about ‘may’ and ‘might’.
May and Might

1. To express (future) possibility.
There is a chance that something is true or that there is a possibility of something happening.
Might is used more frequently than May in spoken English.
It might rain later.
He's very good, in fact, I think he may win the competition.

2. To give permission.
You may take only one brochure.

You may not park your car in front of the gate.

3. To ask for permission.
Can is used more frequently than May in spoken English though May sounds more polite.

May I borrow your pen?
May I use your bathroom please?

Might could also be used to request permission but it sounds very old and is not common.
4. May is used when we talk about typical occurrences.
May is used in academic (or scientific) language to refer to things that typically happen in certain situations.
Adults may find it difficult to sleep if they use technology before going to bed.