Secondary 2 - Grammar - Unit 16
Modal verbs of obligation have to, must, need to
ANSWERS
 
1.
1 - d don't have to (Reason: It's not necessary.)   
2 - b don't need (Reason: This is the only form that fits with to be following it. You mustn't be so rude! and You don't have to be so rude! are possible sentences but don't fit here because to be is already in the sentence.)
3 - b had to (Reason: Yesterday shows that we need the past tense. Had to is the only past tense here.)
4 - c must (Reason: This is the statement of a law. Note the impersonal third person subject [drivers] and the formal language [operating a motor vehicle]. Laws are stated using must.)    
5 - d have to (Reason: It is an obligation imposed from the outside. This is someone talking about a law, not the law itself. Note the personal subject [you] and the informal language.)
6 - c mustn't (Reason: In the negative, this is the only one that means it is necessary not to do something.)
7 - a must (Reason: This is the speaker's own strong feelings or wishes. The speaker is putting the obligation on himself/herself.)   
8 - a Do you have to (Reason: The speaker is asking about something imposed on the listener, something the listener has no choice in, so have to is used. Choice (d) is not the correct form of the question.)    
9 - c don't have to   (Reason: It's not necessary.)    
10 - a mustn't   (Reason: It's necessary that you not do it.)  
11 - b   have    (Reason: The obligation comes from outside, so use have to. We can’t use must because to is already in the sentence.)    
12 - a   must   (Reason: It's urgent. Must is stronger than have to.)
 
2.
 
1. There’s a traffic jam on 6th of October Bridge. We have to/will have to take another road. (Reason: We don’t have any choice about this because of the traffic.)
 
2. Oh, you must take the road through the mountains. It is such a beautiful drive! (Reason: I’m making a strong recommendation to you. I believe it is a good thing to do.)
 
3. In the winter you don’t need to use the air conditioner to cool the room. (Reason: There is no necessity because the weather is cool.)
    In the winter you don’t have to use the air conditioner to cool the room. (Reason: There is no necessity because the weather is cool.)
 
4. You mustn’t use the air conditioner in Dad’s room. He’s sick and shouldn’t get too cold. . (Reason: You are forbidden to do it.)
 
5. You mustn’t repair the machine when it is connected to the electricity. (Reason: This is forbidden for safety reasons.)
 
6. You don’t need to repair the machine today. I can wait until tomorrow. (Reason: It is not necessary.)
    You don’t have to repair the machine today. I can wait until tomorrow. (Reason: It is not necessary. There is no obligation.)
 
7. Listen to me! You must get a new pump soon for the fish tank. This one doesn’t work well. (Reason: I’m giving you strong advice. This is obligatory. This is perhaps the best choice because “Listen to me!” shows that the speaker is saying something important or urgent.)
Listen to me! You have to get a new pump soon for the fish tank. This one doesn’t work well. (Reason: I’m giving you advice. This is obligatory.)
Listen to me! You need to get a new pump soon for the fish tank. This one doesn’t work well. (Reason: I’m giving you strong advice. I think this is necessary.)

8. I really must visit my grandmother in Alexandria more often. (Reason: This is important to me. I am putting this obligation on myself.)
 
9. I often have to go to Alexandria on business. (Reason: I have no choice; it’s part of my work. The obligation comes from outside.)
 
10. Don’t you see that sign? It says “Left lane must turn left.” (Reason: This is a sign stating a traffic rule.) We don’t want to go left. You’ll have to move to the right lane. (Reason: You don’t have a choice because of the rules. The speaker is not stating the rule but talking about what the driver has to do because of the rule.)
 
11. The deadline to apply to university is next week. I have to finish writing my application. (Reason: I have no choice; this is a deadline set by the university.)
The deadline to apply to university is next week. I need to finish writing my application. 
(Reason: This is necessary because of the deadline set by the university. Both answers are correct, but need to is more often used in the negative than in the positive. Have to is more common in speech.)
 
12. My favourite author has written a new novel. I must go buy a copy. (Reason: It’s important to me; it’s something I want to do. I have set this obligation on myself.) 
 
13. Our professor gave us a list of books. I have to buy three books for this course. (Reason: I have no choice; it’s the professor’s decision. It is possible to use the other modals here, but this is the most commonly used one in such a situation.)
 
14. Must you wear that yellow tie? It’s really ugly. (Reason: I am asking if it is important to you to wear it. This also implies that I want you to take it off. It annoys me.)
 
15. Do you have to wear that yellow tie as part of your work uniform? (Reason: I am asking if this is a rule, something that you don’t have a choice about?)
 
16. We have a ten-day holiday. I don’t need to wake up early for ten days! (Reason: It is not necessary.)
    We have a ten-day holiday. I don’t have to wake up early for ten days! (Reason: It is not necessary.)
 
17. Dad worked very late last night. You mustn’t wake him up early today. (Reason: It is forbidden.)
 
18. I really must lose some weight. My clothes hardly fit me anymore. (Reason: It’s important to me in order to look better. I am putting the obligation on myself.)
 
19. The doctor says I have to lose 10 kilos. (Reason: The doctor says it’s obligatory.)
 
20. The boxer has to lose five kilos before his next match or he will be disqualified. (Reason: He doesn’t have any choice or he will be disqualified.)
The boxer needs to lose five kilos before his next match or he will be disqualified.
(Reason: It is necessary if he wants to be in the next match.)
 
21. It says here in the law book: “Cars must have an inspection every two years before the registration can be renewed.” (Reason: This is a law.)
 
22. You have to have the car inspected next week. The registration expires soon. (Reason: The law says you have to do this.)
 
23. We have to get Grandfather to a hospital immediately. He’s very ill. (Reason: The situation makes going to the hospital obligatory.)
    We must get Grandfather to a hospital immediately. He’s very ill. (Reason: The speaker thinks that this is necessary. Must is often stronger than have to.)
    We need to get Grandfather to a hospital immediately. He’s very ill. (Reason: The speaker thinks it is necessary. Need to is often stronger than have to.)
 
3.
1. It was very kind of you to pay for the food but you didn’t need to.
2. Students must not talk when the teacher is speaking.
3. I need to arrive at the meeting on time.
4. I must wake up on time so that I can do everything I planned for tomorrow.
5. To get better grades in English I must study more.
 
 
4.
Tomorrow I have a big business meeting with an important new customer. The meeting starts at 10 but I have to (reason: the situation makes this obligatory) be there very early at 8.30 to organise some things. This means that I will probably have to / need to (reason: it is necessary) take a taxi rather than a bus in the morning. In our company we have to (reason: we have no choice; it’s a rule) wear suits when meeting customers. I had to (reason: it was necessary) have my best suit cleaned for tomorrow. I don’t have to (reason: it is not necessary) prepare my presentation for the meeting tonight because I have already done that. But it is very important that I get enough sleep. I must (reason: This is important to me) go to bed early tonight!
 
 
5.
1 - b     2 - e     3 - d     4 - f     5 - a