Page 544 - Practical English Usage 3ed - Michael Swan, Oxford

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must not used
Should and ought can be used for predictions - to say what people expect to happen. Must is 110t often used in this way.
It should be fine tomorrow. (BUT NOT .'t m!t8t bejine t6I1U:Jff611i.)
Nextweek'sexamshouldbeeasy.(BUTNOT.'V~tlIieek's~mmllstbeemy.) Should have and ought to have + past participle can be used to talk about unfulfilled obligation in the past. Must is not used like this.
You should have been nicer to Annie. (BUT NOT Y8lt m!t8t have been nicer t8 Armie.)
For details of the use of mllst, see 358-361.
For the difference between sholildiolight and had better, see 230.
should (4): in subordinate clauses importance: It's important that . .. should . ..
In formal British English, should can be used in that-clauses after adjectives and nouns expressing the importance of an action (e.g. important. necessary. vital, essential. eager. anxious. concerned. wish).
It's important that somebody should talk to the police. Is it necessary that my uncle should be informed?
I'm anxious that nobody should be hurt.
It is his wish that the money should be given to charity.
This also happens after some verbs expressing similar ideas, especially in sentences about the past.
He insisted that the contract should be read aloud.
I recommended that she should reduce her expenditure.
In a less formal style, other structures are preferred.
It's important that she talks to me when she gets here.
Was it necessary to tell my uncle?
In American English. this use of should is unusual; subjunctives may be used (see 561).
It's important that somebody talk to the police. Was it necessary that my uncle be informed?
I recommend that she reduce her expenditure.
reactions: It's surprising that she should ...
Should is also used in subordinate clauses after words expressing personal judgements and reactions, especially to facts which are already known or have already been mentioned. (This use. too. is more common in British than American English. It is not particularly formal.)
It's surprising that she should say that to you.
I was shocked that she shouldn't have invited Phyllis.
I'm sorry you should think I did it on purpose.
Do you think it's normal that the child should be so tired?
In American English, would is more usual in this kind of sentence.
It was natural that they would want him to go to a good school. (BrE ... that
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they should . ..)
should (4): in subordinate clauses 521
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