Usage: Modals Anatomy -- Part 5 (Must)

I hope you have read the previous entry. Today's the final chapter on modal verbs usage! Must .

There are two main functions for the modal verb Must, 

1. Making deductions or conclusions (highly probable / highly improbable)
2. Stating necessity and Obligation

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The first main function...


Making deductions or conclusions (highly probable):

1. He jumped off a 10-storey building to test his parachute? He must be mad!
2. He's such a snake! Yet she decided to marry him. She must be really in love with him.

However, you never use must not to express the opposite meaning -- that something is highly impossible. We use can't instead.

1. He jumped off a 10-storey building to test his parachute? He can't be that crazy!
2. He's such a snake! Yet she decided to marry him. She can't be that irrational!

Modal Perfect:

He must have done
He can't have done




Express past certainty using must have done / can't have done:
A: I haven't heard from George for years. I have been looking for him all these years.
B: He must have emigrated. Living happily in a place with no telecommunication devices.
A: He can't have left the country. His passport is still with me!
B: He can't have left such important thing with you! You must be joking!




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The second main function...


Stating necessity and obligation (strong tone):

1. We must cut down the level of CO2 released into the atmosphere.
2. You must be here by 7:55pm, the ferry leaves at 8pm sharp.

Alternatively, you can use have (got) to:

1. The fire is spreading fast, we've got to leave now!!!
2. My mum is home! She'll kill me if she knows I have been calling you. I've got to go!

In the negative form, we use must not, in a way similar to can't:

1. Students must not talk during examination.
2. You mustn't talk to my daughter ever again!

Apart from ordering others, we also order ourselves (not order by others):

1. I must stop playing computer games from today onwards.
2. I must learn to keep my promises.

In questions, we only use must:

1. Must I report this case to my boss?
2. Must you get your quotation by today? If not, I have some other pushing matters to handle.

In this second main function expressing necessity and obligation, there isn't a "past tense" for must,  so we use had to:

1. A: When I was a kid, I had to be back home by 5pm after school.
2. B: When I was a kid, I had to go home immediately after school.
3. C: When I was a kid, I had to ride a Mercedez Benz back home after school. If I rode a Toyota, my buttocks would itch!

For indirect speech:

1. A: My mum said that I must stop eating potato crisps. (Must is still use after a past reporting verb -- said)
2. B: I said that you had to / would have to stop listening to your mum. (Use Had to / Would have to)

When an obligation is from external force, or 'outside', we prefer to use have to:

1. I have to go to Tsim Sha Tsui late tonight, I have a meeting to attend.
2. You've to take these meds 3 times a day, the doctor said so.

For the case of future, we use will have to (more polite), have (got) to and must:

1. I will have to go to Beijing next Sunday to attend a conference.
2. You must come back to the office at 10am tomorrow to pack up your belongings. (giving order)
3. You can talk to the patient, but you'll have to leave before 5pm. (More polite because of distancing)
4. I have to attend a reunion dinner with my relatives this Sunday. (Used when program has long been confirmed)

Homework:
Try to explain the meanings of the following sentences in details, you can make your predictions as you wish, just simply focus on the highlighted words:
(Leave comments for me to check)


Paul: Hey Mary, how are you doing?
Mary: Not bad. How are you?
Paul: Same old. You must have been busy. I've been trying to find you.
Mary: Yeah, quite. You sound serious. It must be something important.
Paul: Well, kind of. You see, I have to attend a party organised by my school's alumni next Saturday, and ...
Mary: Sorry Paul, you'll have to speak a little faster cos I'm in a little hurry right now.
Paul: Oh, okay. You see, it is a dance ball, and I will have to have a partner to go with me, and ... I haven't find the wrong person yet.
Mary: It must be really troubling you, huh!
Paul: Ye~ah. So, I ... was was wondering ... if you could ....
Mary: Sure! Why not!
Paul: Really? You know what I was going to say?
Mary: Yeah! Well, I have to go to do some grocery shopping in the morning, but I will be free after that.
Paul: Mary, ...
Mary: Oh! I must get myself a nice evening dress first, ah! Where did I put the one I bought last week?
Paul: Mary, I mean...
Mary: Must I dress according to the theme of the party? What is the theme anyway?
Paul: In fact, the theme is ...
Mary: Oh, doesn't matter. I must dress to my very best, right?
Paul: The theme is "Dance with Your Pets", Mary! I'll have to borrow Mi Mi for a night.
Mary: What? My dog?




Resources:
http://lockyep.blogspot.com/2010/04/usage-modals-anatomy-part-4-may-might.html
http://lockyep.blogspot.com/2009/11/usage-polite-or-impolite-past-vs_13.html
Practical English Usage Third Ed. -- Michael Swan