Can, could, be able to

     

cancould are modal auxiliary verbs. be able to is NOT an auxiliary verb (it uses the verb be as a main verb). We include be able to here for convenience.

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In this lesson we look at can, could and be able to, followed by a quiz to kiểm tra your understanding.

can

Can is an auxiliary verb, a modal auxiliary verb. We use can to:

talk about possibility and abilitymake requestsask for or give permission

Structure of can

The basic structure for can is:

subject+auxiliary verbcan+main verb

The main verb is always the bare infinitive (infinitive without to).

subjectauxiliary verbcanmain verb
+Icanplaytennis.
-Hecannotplaytennis.
can"t
?Canyouplaytennis?

Notice that:

Can is invariable. There is only one form: canThe main verb is always the bare infinitive.
The main verb is always the bare infinitive (infinitive without to). We cannot say: I can khổng lồ play tennis.

Use of can

can for possibility và ability

We use can to lớn talk about what is possible, what we are able or miễn phí to do:

She can drive a car.John can speak Spanish.I cannot hear you. (I can"t hear you.)Can you hear me?

Normally, we use can for the present. But it is possible to use can when we make present decisions about future ability.

Can you help me with my homework? (present)Sorry. I"m busy today. But I can help you tomorrow. (future)
can games for present ability
can for requests & orders

We often use can in a question khổng lồ ask somebody to bởi something. This is not a real question - we vị not really want to know if the person is able to vị something, we want them to bởi it! The use of can in this way is informal (mainly between friends and family):

Can you make a cup of coffee, please.Can you put the TV on.Can you come here a minute.Can you be quiet!can for permission

We sometimes use can to ask or give permission for something:

Can I smoke in this room?You can"t smoke here, but you can smoke in the garden.

(Note that we also use could, may, might for permission. The use of can for permission is informal.)


can/could/may games for present permission

could

Could is an auxiliary verb, a modal auxiliary verb. We use could to:

talk about past possibility or abilitymake requests

Structure of could

subject+auxiliary verbcould+main verb

The main verb is always the bare infinitive (infinitive without to).

subjectauxiliary verbcouldmain verb
+My grandmothercouldswim.
-Shecould notwalk.

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couldn"t
?Couldyour grandmotherswim?

Notice that:

Could is invariable. There is only one form: couldThe main verb is always the bare infinitive.
The main verb is always the bare infinitive (infinitive without to). We cannot say: I could to lớn play tennis.

Use of could

could for past possibility or ability

We use could lớn talk about what was possible in the past, what we were able or không tính tiền to do:

I could swim when I was 5 years old.My grandmother could speak seven languages.When we arrived home, we could not mở cửa the door. (...couldn"t mở cửa the door.)Could you understand what he was saying?

We use I (positive) and couldn"t (negative) for general ability in the past. But when we talk about one special occasion in the past, we use be able to (positive) and couldn"t (negative). Look at these examples:

pastgeneralspecific occasion
+My grandmother could speak Spanish.A man fell into the river yesterday. The police were able to save him.
-My grandmother couldn"t speak Spanish.A man fell into the river yesterday. The police couldn"t save him.

could games for past ability
could for requests

We often use could in a question lớn ask somebody to do something. The use of could in this way is fairly polite (formal):

Could you tell me where the bank is, please?Could you send me a catalogue, please?

be able to

Although we look at be able to here, it is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We look at be able to here because we sometimes use it instead of can and could.

We use be able to:

to talk about ability

Structure of be able to

The basic structure for be able to is:

subject+be+able+to-infinitive
subjectmain verbbeadjectiveableto-infinitive
+Iamableto drive.
-Sheis notableto drive.
isn"t
?Areyouableto drive?

Notice that be able to is possible in all tenses, for example:

I was able to drive...I will be able to drive...I have been able to drive...

Notice too that be able to has an infinitive form:

I would lượt thích to be able to speak Chinese.

Use of be able to


Be able to is NOT a modal auxiliary verb. We include it here for convenience, because it is often used lượt thích "can" and "could", which are modal auxiliary verbs.

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be able to for ability

We use be able to to lớn express ability. "Able" is an adjective meaning: having the power, skill or means to do something. If we say "I am able to swim", it is lượt thích saying "I can swim". We sometimes use be able to instead of "can" or "could" for ability. Be able to is possible in all tenses - but "can" is possible only in the present và "could" is possible only in the past for ability. In addition, "can" và "could" have no infinitive form. So we use be able to when we want to lớn use other tenses or the infinitive. Look at these examples:

I have been able to swim since I was five. (present perfect)You will be able to speak perfect English very soon. (future simple)I would like to be able to fly an airplane. (infinitive)can, could, be able to Quizgiayphutyeuthuong.vn : Learn English : Grammar : Verbs : Modals : can, could, be able to

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