Intermediate Grammar: Should, must and have to

SHOULD, MUST AND HAVE TO 

• Should  - We use should to give an advice
• Must and have to - We use must and have to for obligations

SHOULD

• Advice: If you feel bad, you should go to the doctor. 
• Obligation (in a polite way): Anyone who wants to enter the concert should show his ticket. 

Should in present: You should tidy your bedroom. 

Should in past: She should have finished her composition yesterday. 

Should in future: Tomorrow you should call your grandfather, it's his birthday. 

Should in negative: You shouldn't smoke. 

Should in interrogative: Should we wear an umbrella?

MUST AND HAVE TO .- Diferences between must and have to 

• Must: Obligation imposed by the speaker. 
• Have to: Obligation imposed by an external agent or Strong personal obligation imposed by the speaker. 

MUST: It is always followed by an infinitive verb without to. 

• We must wait
• You mustn't smoke
• Why must we be quiet?

HAVE TO: it is always followed by an infinitive verb with to. 

• I have to study Maths. 
• We don't have to go.
• Why doesn't he have to wear uniform?