can 与be able to的区别与用法

can泛指一般的能力

而be

able

to

指具体做某件事

的能力

如:

He

can

swim.

I

am

able

to

express

my

idea

in

a

clear

way.

表过去时

could

常表示过去有能力做某事

但不一定去做，而was/were

able

to则表示过去能够做某事并成功的做了

如：I

could

catch

the

6.30

train

表示过去有能力赶上六点半的火车

但不一定赶了

I was

able

to catch

the

6.30

train

表示过去有这个能力

并且成功的赶上了

(1)

be

able

to

强调通过努力而获得的能力,而can则强调自身已具有的能力.如：

She

can

sing

the

song

in

English.她能用英语唱这首歌.

He

will

be

able

to

sing

this

song

in

English

in

a

few

minutes,too.几小时之后,他也能用英语唱这首歌.

(2)

be

able

to

强调一种结果,而can只强调一种可能.如：

Luckily,he

was

able

to

escape

from

the

big

fire

in

the

end.幸运的是,他终于逃出了大火.

If

he

got

here

a

few

hours

earlier,I

could

save

him.要是他早几小时来,我还能救他.

(3)

be

able

to

可以有各种时态；而can只有一般现在和一般过去两种时态.如：

I

could

help

you

last

night,but

you

didn’t

come.昨天晚上我能帮你,而你又没来.

Can

you

see

it

there?你能看见它在那儿吗?

He

is

/

was

/

will

be

able

to

help

you.他能帮你的忙

Will

you

be

able

to

camera

the

lecture

tomorrow?你明天能把讲座录下来吗?

I'm

sorry

I

haven't

been

able

to

answer

your

letter

in

time.真对不起我没能及时给你回信.

Ps:指过去某时或某个时刻设法做成某事,不用could,而用was\were

able

to.

I

talked

with

her

for

a

long

time,and

eventually

I

was

able

to

make

her

believe

me.我谈了很久,最终还是使她相信了我的话.

(4)

can可用于表示可能性,推测,允许等情况,而be

able

to通常不这样用.

You

are

able

to

use

my

pen.(误)

You

can

use

my

pen.(正)

(5)

can有被动语态,主语为人或物皆可,而be

able

to只接不定式的主动形式,不接表示被动的不定式,也不可用无生命的名词作主语.例如：

The

work

is

able

to

be

done

by

him.（误）

He

is

able

to

do

the

work.（正）

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