Page 541 - Practical English Usage 3ed - Michael Swan, Oxford

We use do if there is no other auxiliary. She likes cakes. - She really does. That surprised you. - I t certainly did.
Non-auxiliary be and have are used in short answers. Is she happy?- I think she is.
Have you a light?- Yes, I have.
Short answers can be followed by tags (see 487-488). Nice day. '" Yes, it is, isn't it?
Note that stressed, non-contracted affirmative forms are used in short answers.
Yes, I am. (NOT Yes, Pm.)
For similar structures. see 484 (reply questions). 487-488 (question tags) and 181 (ellipsis). For So am I etc, see 541.1.
For So I am etc, see 541.2.
518 should (1): introduction 1 forms
Should is a modal auxiliary verb (see 353-354). It has no -s in the third person singular.
The postman should be here soon. (NOT The p6stmtm sh6ftltls ...) Questions and negatives are made without do.
ShouldwetellJudy?(NOT lJtJweshould...?) Should is followed by an infinitive without to.
Should I go? (NOT Sh6Uld : 16 g6?)
She should be told the truth.
There is a contracted negative shouldn't.
The meeting shouldn't take long.
Should has a weak pronunciation /jad/, often used when it is not stressed (see 616).
2 obligation, probability
Should can be used to talk about obligation: things that it is good or important for people to do (see 519.1).
Everybody should wear car seat belts.
It can also be used to say what we think is probable, because it is logical or normal (see 519.2).
She's away, but she should be back tomorrow.
With these meanings, should is like a weaker form of must.
3 It is important/surprising that . .. should ...
Should is used in that-clauses after certain adjectives and nouns, especially in British English (see 521).
It's important that somebody should talk to the police. It's surprising that she should say that to you.
..
should (1): introduction 518
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