Should is a modal auxiliary verb. In the third person singular, it has no –S.For example:
1. The teacher should be here soon. – (You do not say “ The postman should…”)
Questions and negatives are made without do.For example:
1. Should we tell Mabelle? – (You do not say “Do we should…?”)
Should is followed by an infinitive without to.For example:
1. Should I come? (You do not say – “Should I to go?”)
2. She should be told the reality.
There is a contracted negative shouldn’t.For example:
1. The class shouldn’t take long.
Please note: Should has a weak pronunciation – often used when it is not stressed.
Should can be used to talk about obligation: things that is good or important for people to do.For example:
1. Everyone should wear a cap.
It can also be used to say what we think is probable, because it is logical or normal.For example:
1. She is at home, but she should be at the office tomorrow.
With these meanings, should is like a weaker form of must.
Should is used in that-clauses after certain adjectives and nouns, especially in British English.For example:
1. It’s important that somebody should talk to Anna.
2. It’s surprising that she should do that to you.
Should can be used in if-clauses, after “in case” after “for fear that” and “lest” and after “so that” and “in order that”.For example:
1. If you should see Dana, tell her I’ve got the books.
2. I’ll get the fruits out of the basket in case Uncle Boy should come.
3. He turned the radio down so that he shouldn’t disturb the old lady.