Should – to express weak obligation and advice
The modal verb should expresses weaker obligation than must and have to.
|Should – to express obligation|
|Structure: should + infinitive form of a verb:
should be, should go, should do, etc.
We use should for the present and the future.
|You should tell them the truth.
You shouldn’t smoke, it’s bad for you.
I don’t think you should do it.
Should have – for unfulfilled past obligation
|Should have – to express unfulfilled obligation in the past|
|Structure: should + have + past participle
We use should have for the past.
|You should have told them the truth.
You shouldn’t have gone there – it was a mistake.
I don’t think you should have done it.