This document provides information about modal auxiliary verbs in English. It defines modal verbs as verbs that are always followed by an infinitive without "to" and have no past tense or third person -s forms. Common modal verbs discussed include can, could, may, might, must, should, have to, need to, and their uses for ability, permission, certainty, obligation, suggestions, deductions and more. Examples are given for each modal verb. There is also a table that shows the probability implied by different modal verbs. An exercise follows with 25 sentences for the reader to practice using modal verbs.

1. English Department
Modal verbs CPI Tino Grandío
MODAL AUXILIARY VERBS
 They are always followed by another verb in the infinitive without to.
o You shouldn't smoke.
 They have no -(e)s on the third person singular.
o He can't swim.
 Questions and negatives are made without do.
o If I were you I wouldn't do that.
 Modal verbs have no infinitives; other expressions have to be used instead, when an infinitive is necessary.
o I want to be able to swim. (Not: *I want to can swim.)
o I had to visit her yesterday. (Not: *I must visit her yesterday.)
 Modal verbs have no past forms (could and would are sometimes used with a past meaning).
CAN (BE ABLE TO)
 We use can (/kæn/, /kən/) when we want to say that something is possible or somebody has the ability to do
something.
o You can dance very well.
 Can may be used for suggestions:
o We can go to the new swimming pool in the afternoon.
 Be able to is used when an infinitive (or another tense) is needed:
o They will be able to speak French next year. (Not: *They will can speak French next year.)
o We haven’t been able to finish on time.
 In the negative can't (/kɑ:nt/) is used:
o We can't speak German well.
 Can't is used when we realize that something is impossible:
o It can't be true.
COULD
 Could (/kʊd/, /kəd/) is used for past ability:
o When I was 7 I could read and write very well.
 It is also used for deduction, when we think that something is possible:
o They could be right about that.
 Could is used when asking permission:
o Could I borrow your red pen?
MAY / MIGHT
 May (/meɪ/) is used when asking permission (it's more formal than could):
o May I go to the toilet? Yes, of course.
 We use may or might to say that something is possible:
o It may / could / might rain this afternoon.
MUST
 Must (/mʌst/) is used when we know that something is necessary:
o You must study harder, otherwise you'll fail.
 In the negative it means negative obligation:
o You mustn't lose my key. It's the only one I have.
 Must is also used when we are certain about something:
o They aren't answering the phone. They must be out.
SHOULD / SHOULDN'T
 Should and shouldn't are used for giving advice:
o You should lose some weight if you want to be healthy.
o We shouldn't wait any longer.
HAVE TO / DON'T HAVE TO
 Have to is not really a modal verb as it doesn't share all their characteristics.
 Have to is used to provide all the tenses that must doesn't have:
o He will have to come with me tomorrow.
 In the negative don't/doesn't have to means lack of obligation (≠ mustn't)
 You don't have to finish the exercises today. You can do them at the weekend.
NEED / NEEDN’T
 Need to, just as have to does, expresses obligation. It can be used in all the tenses.
o I need to finish it now. They can’t wait.
 In the negative you can use don’t/doesn’t need to, or the more formal needn’t + bare infinitive:
o You don’t need to help me. / You needn’t help me.
PROBABILITY
- MUST 100%
- MAY 50%
- MIGHT 30%
- COULD 30%
- CAN'T 0%

2. EXERCISE:
1. I'm hungry. I think I ______________ have a sandwich.
2. You have been working very hard. I think you ______________ have a break.
3. You ______________ be patient. You can't always get things immediately.
4. ______________ go to the toilet?
5. We have run out of milk. You ______________ go to the supermarket and buy two cartons.
6. I'm not sure. I ______________ pass this exam.
7. ______________ you swim? Yes, but not very well.
8. ______________ you turn off the radio? I can't speak to your brother.
9. Rebecca is very intelligent. She ______________ speak five languages.
10. I forgot to phone my mother last night so I ______________ phone her today.
11. Isn't this classroom too hot? I ________________ open the window.
12. You ______________ speak to your mother like that. She will be very upset.
13. We ______________ ride a bike but we ______________ ski.
14. If I am not better I ______________ not go to work tomorrow.
15. Look at my shoes! They are so dirty. I ______________ clean them now.
16. Last night I was very tired but I ______________ sleep.
17. Your father ______________ smoke so much if he wants to get better soon.
18. Some of his friends ______________ go to the school trip because they had flu.
19. It ______________ be your sister. (= I'm sure it is your sister.)
20. Have you seen my keys? I ______________ find them.
21. (She doesn't know yet) My cousin ______________ come to the party.
22. ______________ I smoke here?
23. I wasn't hungry yesterday evening so I ______________ finish my dinner.
24. This is an excellent film. You ______________ watch it. I'm sure you'll love it as much as I did.
25. I'm sorry but I ______________ go to your birthday party next week.
26. Take an umbrella. It ______________ rain.
27. I don't think you ______________ spend so much money on clothes.