ENGLISH GRAMMAR ; MODALS : MUST AND SHOULD

Sometimes you prohibit someone from doing something. In other occasions, you encourage someone to do something or even make him/her do something. You should do it properly and politely. By doing it properly,people will understand you easily. By doing politely, people will be happy to your suggestion or the obligation. In this chapter, you will learn about instructing comply with prohibiting and encouraging.

A. Must

"Must" is also used to talk about obligation and is used in written rules and instructions:
You must submit your proposal by noon on 12th July.
You must not use a calculator during the exam.

"Must" is also used to give a strong recommendation:
You must tell him before it's too late.
You mustn't be late for work on your first day.

Form

"must" or "mustn't" ("must not") + the infinitive of the verb (without "to")

B. Should

We use "should" to give, or ask for, advice or an opinion in the present:

Example :
"I have a terrible stomachache." "You should go to the doctor's."
"I haven’t heard from my father." "You should call him."
"She's not happy with the salary offered." "She shouldn't accept the job."

Form

We use "should" / "shouldn't" + the infinitive of the main verb (without "to")

Should have

We use "should have" to give, or ask for, an opinion in the present about something which happened in the past:

• "I had a terrible stomachache." "You should have gone to the doctor’s."
• "I didn’t hear from my father last week." "You should have called him."
• "She isn't happy with the salary she’s getting." "She shouldn't have accepted the job."

Form

We use "should" / "shouldn't have" + the past participle of the main verb