should

Từ điển Oxford Advanced Learner 8th

should BrE [ʃəd] NAmE [ʃəd] BrE strong form [ʃʊd] AmE strong form [ʃʊd] modal verb (negative should not, short form shouldn'tBrE [ˈʃʊdnt] ; NAmE [ˈʃʊdnt] )
1. used to show what is right, appropriate, etc, especially when criticizing sb's actions
• You shouldn't drink and drive.
• He should have been more careful.
•A present for me? You shouldn't have! (= used to thank sb politely)
2. used for giving or asking for advice
•You should stop worrying about it
• Should I call him and apologize?
•I should wait a little longer, if I were you.
• (ironic)‘She doesn't think she'll get a job.’ ‘She should worry, with all her qualifications (= she does not need to worry).’
3. used to say that you expect sth is true or will happen
• We should arrive before dark.
• I should have finished the book by Friday.
•The roads should be less crowded today.
4. used to say that sth that was expected has not happened
• It should be snowing now, according to the weather forecast.
• The bus should have arrived ten minutes ago.
5. (BrE, formal)used after I or we instead of would for describing what you would do if sth else happened first
•If I were asked to work on Sundays, I should resign.
6. (formal)used to refer to a possible event or situation
• If you should change your mind, do let me know.
• In case you should need any help, here's my number.
•Should anyone call (= if anyone calls), please tell them I'm busy.
7. used as the past form of shall when reporting what sb has said
• He asked me what time he should come. (= His words were: ‘What time shall I come?’)
• (BrE, formal)I said (that) I should be glad to help.
8. (BrE)used after that when sth is suggested or arranged
• She recommended that I should take some time off.
• In order that training should be effective it must be planned systematically.  In both NAmE and BrE this idea can be expressed without ‘should’
•She recommended that I take some time off.
•In order that training be effective…
9. used after that after many adjectives that describe feelings
• I'm anxious that we should allow plenty of time.
• I find it astonishing that he should be so rude to you.
10. (BrE, formal)used with I and we in polite requests
• I should like to call my lawyer.
• We should be grateful for your help.
11. used with I and we to give opinions that you are not certain about
• I should imagine it will take about three hours.
• ‘Is this enough food for everyone?’ ‘ I should think so.’
•‘Will it matter?’ ‘ I shouldn't think so.’
12. used for expressing strong agreement
•‘I know it's expensive but it will last for years.’ ‘ I should hope so too! ’
•‘Nobody will oppose it.’ ‘ I should think not! ’
13. why, how, who, what ~ sb/sth do used to refuse sth or to show that you are annoyed at a request; used to express surprise about an event or a situation
•Why should I help him? He's never done anything for me.
•How should I know where you've left your bag?
•I got on the bus and who should be sitting in front of me but Tony!
14. used to tell sb that sth would amuse or surprise them if they saw or experienced it
•You should have seen her face when she found out!

Word Origin:
[should] Old English sceolde: past of ↑shall.

Grammar Point:
modal verbs
The modal verbs are can, could, may, might, must, ought to, shall, should, will and would. Dare, need, have to and used to also share some of the features of modal verbs.
Modal verbs have only one form. They have no -ing or -ed forms and do not add -s to the 3rd person singular form: ▪ He can speak three languages. ◇ ▪ She will try and visit tomorrow.
Modal verbs are followed by the infinitive of another verb without to. The exceptions are ought to and used to: ▪ You must find a job. ◇ ▪ You ought to stop smoking. ◇ ▪ I used to smoke but I gave up two years ago.
Questions are formed without do/does in the present, or did in the past: ▪ Can I invite Mary? ◇ ▪ Should I have invited Mary?
Negative sentences are formed with not or the short form -n’t and do not use do/does or did.
You will find more help with how to use modal verbs at the dictionary entries for each verb.

Grammar Point:
should / ought / had better
Should and ought to are both used to say that something is the best thing or the right thing to do, but should is much more common: ▪ You should take the baby to the doctor’s. ◇ ▪ I ought to give up smoking. In questions, should is usually used instead of ought to: ▪ Should we call the doctor?
Had better can also be used to say what is the best thing to do in a situation that is happening now: ▪ We’d better hurry or we’ll miss the train.
You form the past by using should have or ought to have: ▪ She should have asked for some help. ◇ ▪ You ought to have been more careful.
The forms should not or shouldn’t (and ought not to or oughtn’t to, which are rare in NAmE and formal in BrE) are used to say that something is a bad idea or the wrong thing to do: ▪ You shouldn’t drive so fast.
The forms should not have or shouldn’t have and, much less frequently, ought not to have or oughtn’t to have are used to talk about the past: ▪ I’m sorry, I shouldn’t have lost my temper.

Grammar Point:
should / would
In modern English, the traditional difference between should and would in reported sentences, conditions, requests, etc. has disappeared and should is not used very much at all. In spoken English the short form 'd is usually used: ▪ I said I’d (I would) be late. ◇ ▪ He’d (he would) have liked to have been an actor. ◇ ▪ I’d (I would) really prefer tea.
The main use of should now is to tell somebody what they ought to do, to give advice, or to add emphasis: ▪ We should really go and visit them soon. ◇ ▪ You should have seen it!