Contents introduction chapter I grammatical meaning, grammatical form

You use 'should' and 'ought' to talk about mild obligation.
You can use ' should' and 'ought' to talk about a mild obligation to do something. When you use 'should' and 'ought', you are saying that the feeling of obligation is not as strong as when you use 'must'.
Should' and 'ought' are very common in spoken English. Should' is followed by the base form of a verb, but 'ought' is followed by a 'to'-infinitive.
When you want to say that there is a mild obligation not to do something, you use 'should not', 'shouldn't, 'ought not', or 'oughtn't'.
You use 'should' and 'ought' in three main ways:
- when you are talking about what is a good thing to do, or the right thing
to do.
We should send her a postcard.
We shouldn 't spend all the money. He ought to come more often. You ought not to see him again.
- when you are trying to advise someone about what to do or what not to
do.
You should claim your pension 3-4 months before you retire.
You shouldn't use a detergent. You ought to get a new TV. You oughtn 't to marry him.
- when you are giving or asking for an opinion about a situation. You
often use ^л1 think', ^л1 don't think', or 'Do you think' to start the sentence.
/ think that we should be paid more.
I don't think we ought to grumble.
Do you think he ought not to go?
What do you think we should do? You use ^л should have' or^л ought to have' and a past participle to say that there was a mild obligation to do something in the past, but that it was not done. For example, if you say ^л1 should have given him the money yesterday', you mean that you had a mild obligation to give him the money yesterday, but you did not give it to him.
/ should have finished my drink and gone home.
You should have realized that he was joking. We ought to have stayed in tonight.
They ought to have taken a taxi.
You use ' should not have' or' ought not to have' and a past participle to say that it was important not to do something in the past, but that it was done. For example, if you say 'I should not have left the door open', you mean that it was important that you did not leave the door open, but you did leave it open.
/ should not have said that.
You shouldn't have given him the money.
They ought not to have told him.
She oughtn 't to have sold the ring.
You use 'had better' followed by a base form to indicate mild obligation to do something in a particular situation. You also use 'had better' when giving advice or when giving your opinion about something. The negative is 'had better not'.
/ think I had better show this to you now.
You'd better go tomorrow.
I'd better not look at this.
The correct form is always 'had better' (not 'have better'). You do not use 'had better' to talk about mild obligation in the past, even though it looks like a past form.