Expressing Necessity and Expectation

When we are thinking of saying something necessary or expectation, we can use the following expressions:

No.	Necessity	Expectation
1	Have to	To be supposed to
2	Must	should
3	Need	Ought to
4	Be necessary	Be expected to

Examples:

      1.       You have to pay taxes if you run a business.

      2.       You must prepare yourself for the upcoming exams.

      3.       I need to talk to you for a second.

      4.       It is necessary to follow all instructions precisely.

      5.       You are supposed to come to meetings on time.

      6.       We should leave now if we don’t want to miss the show.

      7.       They ought to work hard and smart to get a promotion.

      8.       You are expected to show your best performance in the match.

Have to VS Must

Betty Azar says in Fundamentals of English Grammar (3^rd ed) page 206 that Have to and must have basically the same meaning. Have to is usually used in questions, not must.

However, Raymond Murphy says in English Grammar in Use with Answers (2^nd ed) page 62 that must is personal. We use must when we give our personal feelings. While have to is impersonal. We use have to for facts, not for our personal feelings.

Examples:

She’s a really nice person. You must meet her. (=I say this is necessary)

You can’t turn right here. You have to turn left. (because of the traffic system)

Compare:

I must get up early tomorrow. There are a lot of things I want to do.

I have to get up early tomorrow. I’m going away and my train leaves at 7.30.