Verbos Modais

Em inglês, verbos auxiliares modais são verbos que só ocorrem na presença de outro verbo, são defectivos na conjugação e não têm passado nem futuro (com exceção do can que tem passado e condicional).
Devido à alta freqüência com que ocorrem na língua, os verbos modais tornam-se imprescindíveis. Veja aqui uma lista dos principais:

can - could

- significado de ability: I can speak English - Eu consigo falar inglês.
- significado de permission: Can I smoke here? - Posso fumar aqui?
- significado de possibility: It can happen to anyone. - Isso pode acontecer com qualquer um. (Esta ocorrência é mais rara e o significado de possibilidade aqui se confunde com o de capacidade. Para possibilidade é sempre melhor usar may e might.)
Veja aqui um rápido estudo sobre a diferença de pronúncia entre can e can't.

Could funciona como passado e como futuro do pretérito de can:

- passado: I couldn't speak English before going to England. / I co uldn't go. / You couldn't smoke in the presence of your parents at that time. - Eu não sabia falar inglês antes de ir para a Inglaterra. / Não pude ir. / Não se podia fumar na presença dos pais, naquela época.

- futuro do pretérito: You could have called me. Could you do me a favor? - Você poderia ter me ligado. / Você poderia me fazer um favor?

may

- significado de permission: May smoke here? - Posso fumar aqui?
- significado de possibility: It may rain today. - Pode ser que chova hoje.
- para expressar um desejo (to express a wish): May all your dreams come true. - Que todos seus sonhos se realizem. (Esta última ocorrência é mais rara, restrita a uma linguagem mais formal.)

might

- significado de remote possibility: It might rain this weekend. - É capaz de chover no próximo fim de semana.

should - significado de advice: You should study more. - Você deveria estudar mais.*

shall - significado de suggestion (predominante no dialeto britânico): Shall we go to the movies? - Que tal irmos ao cinema? / Que tal, vamos ao cinema?

Shall ocorre unicamente no modo interrogativo e na primeira pessoa do singular (I) ou do plural (we).
must

- significado de obligation: You must stop smoking. - Você tem que parar de fumar.
- significado de prohibition: You mustn't get out of bed. - Você não pode sair da cama.
- significado de inference, logical deduction: He must be very rich. - Ele deve ser muito rico.*
* Veja a ambivalência do verbo dever do português.

Há quem classifique o will, o would e o used to como verbos modais. Nós preferimos deixar o will e o would como auxiliares do future e do conditional, e o used to como habitual, equivalente ao pretérito imperfeito do português. Leia aqui sobre o used to.

Também o verbo need pode ocorrer como modal, mas apenas nas formas negativa e interrogativa. Esta, entretanto, é uma ocorrência muito rara, principalmente em inglês norte-americano.

Fonte: www.english.sk.com.br

VERBOS MODAIS

Absence of obligation

When we want to say that it is not necessary to perform an action we can useneedas a modal in the negative or as a full verb in the negative form as well. But we can also usedon't have toorhaven't got to, which is more informal.

 

Absence of obligation

Present need not (needn't) do not need to (don't need to) / does not need to (doesn't need to) do not have to (don't have to) / does not have to (doesn't have to) have not got to (haven't got to) / has not got to (hasn't got to) Past need not have (needn't have) did not need to (didn't need to) did not have to (didn't have to) had not got to (hadn't got to) Future need not (needn't) shall not need to (shan't need to) / will not need to (won't need to)

Uses

.When we want to say that it isn't necessary to do something we can useneedn't, don't need to, don't have to or haven't got to.Needn'tis normally used to express the speaker's authority while the other forms refer to external authority. However,needn'tcannot be used in present habitual actions. .In the past we useneedn't+perfect infinitive,didn't have toordidn't need to(bothhaveandneedare stressed in speech) to say it wasn't necessary to do something, but we did. Instead we usedidn't have to,didn't need to(without stress) orhadn't got toto say we knew in advance that it wasn't necessary to do something so we didn't.

On Sunday

It is said that Sunday is the best day of the week because you don't have to work and you haven't got to wake up early. You don't need to have breakfast quickly and you can read the newspaper as long as you want. This is true, but today is Sunday and I am in my utility room. What can I see? An iron, a broom, a washing machine, a full laundry basket, a feather duster and a vacuum cleaner. What do I use them for? To do the housework. This means that I will have to spend the whole Sunday using the window cleaner, the mop and the dustpan. But people say that on Sunday you don't have to work and you haven't got to wake up early. You don't need to have breakfast quickly and you can read the newspaper as long as you want. So, what is happening? Maybe people forget that some Sundays you must work at home. It is true you don't have to go to work to your office or to your shop but the laundry detergent, the bleach and the softener are waiting for Sunday to be used.

Ability

Modals are auxiliary verbs which are used with a bare infinitive to express the speaker's attitude as well as a degree of certainty or uncertainty. Each modal verb has more than one use. When we want to say that someone has the ability to do something we usecan, but ascanonly has two forms —canfor the present andcouldfor the past —be able tosupplies the missing parts ofcanand it is also an alternative form for present and past.

 

Present
Affirmative can am / is / are able to Negative cannot am not / is not / are not able to Questions can? am / is / are able to?

We express ability in all other tenses by means of the right form of be able to.

Past
Affirmative General ability could was / were able to Specific ability was / were able to Negative General ability could not was not / were not able to Specific ability was not / were not able to Questions General ability could? was / were able to? Specific ability was / were able to?

 

Uses

.Bothcanandam/is/are able tomay be used to express ability in the present althoughcanis the more usual form. .When we refer to past ability we usecouldorwas/were able towhereas we only usewas/were able towhen we want to say that somebody managed to do something in a particular situation in the past. However, in the negative we may usecouldn'tto talk about a particular action not successfully completed. .We normally usecanandcouldwith verbs of senses instead of the simple present.

An afternoon at home

The Robinsons are spending the afternoon at home.

Father- Hey, Peter. I think your brother has some problems with his maths exercises. Why don't you stop playing with the logs and the fireplace and go to his room to help him?
Peter- Can't he solve his maths problems himself?
Father- No, he can't. I'd like to help him, but you know I can't, because I've forgotten what I was taught when I was at school. And your mother could help you when maths was easier. Now it is very complicated.
Peter- Mum, what are you doing?
Mother- I'm sewing the curtains.
Peter- When are you going to teach me how to sew?
Mother - Very soon. If you help your brother, I'll teach you to sew. There are not many boys of your age who can sew. And don't talk so loud. The baby can't sleep, because you are making too much noise.
Peter- Dad, what are you doing?
Father- I'm very busy. Yesterday mum told me something about changing the armchair and the sofa, and I'm just trying to convince her that they are still comfortable. You know it's difficult to convince your mother. Please, go and help your brother. You are the only one who can do it. Your mother and I don't remember anything of what he is doing.
Peter- OK. I'll do it. Mum, don't forget to tell daddy that the TV and the video cassette recorder don't work properly and that it would be a good idea to change them too.

Obligation

We can express obligation or necessity by means of the modal verbmustor the semi-modalhave to. Asmustis only used in the present and future, all other verb tenses are supplied by a form ofhave to

Obligation
Affirmative         Speaker's feelings   External Obligation Present must   have/has to have/has got to Past   had to had got to   Future must   shall/will have to Questions         Speaker's feelings   External Obligation Present must?   do/does ... have to? have/has ... got to? Past   did ... have to? had ... got to?   Future must?   shall / will have to?

Uses

.We usemustfollowed by a bare infinitive to express obligation in the present and future when the obligation is imposed by the speaker. When the obligation comes from a situation, that is to say, it is an external obligation, we usehave toorhave got to.Have tocan be used for both habitual and single actions, buthave got tois only used for single actions. .If the obligation comes from the speaker´s feelings or it is an external obligation, it cannot be expressed in any other verb tense. .Must not(ormustn't) expresses a negative obligation imposed by the speaker.

My first physical education lesson

I remember my first physical education lesson perfectly. I was really impressed by the gym and by my teacher. The gym was fully-equipped: the rings, the vaulting horse, the parallel bars, the wall bars. My teacher was a fit young boy. He was as fit as a fiddle. 'Good morning,' he said, 'Let me introduce myself. I'm your physical education teacher and my name is Ken. This year we are going to use all the equipment you can see and you must train hard to pass the subject easily. There are some rules you have to keep. The first one is that you have to wear your school track suits and gym shoes during the gym hour. The second one is that you mustn't do any dangerous exercise without my consent because you may hurt yourselves. You must be careful. And the third one is that you have to take care of all the equipment. You mustn't play with the rope or the trampoline because they may break. I'm sure that if you follow my instructions and my advice, we'll enjoy together'.'My God!,' I thought. 'I must train hard. I want to be like him'.Today, twenty years after that first gymnastics lesson, I'm still trying to be as fit as my PE teacher was.

Offers, invitations, requests, permission
We use the modals mentioned below to express offers, invitations and requests (including requests for permission).

Offers
Offering food and drink would you like? Offering to do something for others I / we can can I / we? shall I / we?

 

Requests
Asking for something can could may might I / we have? Asking people to do something can could would will you?

 

Permission
Asking for permission can could may might I? Giving and refusing permission you can (not) may (not)

 

Invitations
would you like? will you?

 

Uses
We usecan,could,mayormightdepending on the situation. .Canis the most informal .Couldis more polite thancan. .Mayis more formal thancanandcould. .Mightis the most polite but the least common.

At a party

Frank- Hello. This is Frank. Is that you, Tom?
Tom- Yes, it's me.
Frank- How are you? Would you like to come to my birthday party? It's on Sunday at five in the afternoon.
Tom- I'm sorry, but I had other plans already. My mother asked me to go with her to the bowling alley on Sunday.
Frank- Come on, Tom. You can't miss my party. It will be great. There will be an enormous cake, blowers, streamers, masks, good music and pretty girls. Why don't you ask it to your mother?
Tom- Good idea. Could you wait a moment, please? (Tom speaks to his mother) Mum, Frank is on the phone. His birthday is on Sunday and he's invited me to his party. I know you asked me to go to the bowling alley with you, but we can go next Sunday. May I go to Frank's party?
Tom's mother- Yes, of course.
Tom- Frank, she has agreed. Can I do something to help you with the party? Shall I bring something? I don't know, maybe sweets, crisps, pizza or ice cream.
Frank- Yes, please. I'm sure we'll have a great time. So, see you on Sunday.
Tom- Thank you for your invitation. See you then.

Possibility

We usemay,might,canorcouldwith a bare infinitive to express different degrees of possibility about a present or future situation. When we want to say there was a possibility of something happening in the past we usemay have,might haveorcould havefollowed by the past participle (Perfect Infinitive).

Present and Future
Affirmative Negative Questions may / might / can / could may not might not (mightn't) cannot (can't) could not (couldn't) may?* / might? / can? / could?

*Not normally used at the beginning of a question.

Past
Affirmative Negative Questions may have might have could have may not have might not have(mightn't have) cannot have (can't have) could not have (couldn't have) may ... have? might ... have? could ... have?

 

Uses

.We usemay, might,canorcouldfollowed by a bare infinitive to express the idea that something is possible.Maynotormight notexpress that something negative is possible andcannotorcould notthat something is impossible. .When we want to say it is possible that something happened in the past we usemay, mightorcouldfollowed by the Perfect Infinitive without to (have + Past Participle). .The negative formsmay not haveormight not haveare used to say that something possibly didn't take place whereascannothaveorcould not havemean it is impossible that something happened.

In the library

Johnny- Hello. This is Johnny. May I talk to Sue?
Sue's mother - Hello, Johnny. This is Sue's mother. How are you?
Johnny- Fine, thank you. And you?
Sue's mother- Fine. I'm afraid Sue isn't at home. The literature teacher has asked her to write a composition about Oscar Wilde and she might be in the public library.
Johnny- In the library?
Sue's mother- Yes. I don't know exactly what she is doing there. She may be looking up some information about the author.
Johnny- But there's a library at school, too.
Sue's mother- I know, but it's closed now and she might need more information. You know. She could just need a quiet atmosphere.
Johnny- I've never been to the public library.
Sue's mother- Sue says it is very good. There is a microfilm reader and a photocopy machine and there are also lots of interesting magazines. Sue says that the librarian and the library clerks are very nice. They help you in everything.
Johnny- I may go to visit Sue and help her.
Sue's mother - She will be happy. But remember I'm not sure she is there.
Johnny- Ok. I'll try to meet her. Nice to talk to you.
Sue's mother- Bye.
Johnny- Goodbye.

Fonte: www.escolavesper.com.br