英语:单词Can和be able to的区别

单词Can和词组be able to都表示“能够”做某事,在某些情况下可以互换,但在其它情况下则不能。下面简单说一下Can 和be able to的用法及区别。
1, Can 和be able to用于一般现在时,两者可以换

  • I can’t swim.
  • I am unable to swim (be unable to 是be able to的反义词组)

上面两个句子中,be able to相对更正式些。

2, Can 和be able to用于一般过去时,形式变为could或was able to / were able to
2.1 两者表示一般情况下“能够”做某事时可以互换

  • I could swim (or I couldn’t swim ) when I was 7 years old
  • I was able to swim (or I was unable to swim ) when I was 7 years old

2.2 当用来表示过去特定事件中,“能够”做某事时,要用was able to / were able to。比如,一次划船的经历中,我掉下了水,但我靠自己返回了船上,可以说

  • I was able to swim back to the boat.

此句表示过去特定的这个事件中,我可以游回到船上。这种情况下,我们不能说:

  • I could swim back to the boat.

但是,如果表示过去特定情况下“不能”做某事时呢?比如我掉下了船,但自己是靠别人救上来的,因为我不会游泳。这时就couldn’t或wasn’t able to/was unable to都可以用。

  • She wasn’t able to swim back to the boat
  • She was unable to swim back to the boat.

3, 如果在将来时、现在完成时和过去完成时呢?这种情况下只用词组be able to,而不用单词can. 同时,unable to比not able to要更正式。
3.1, 将来时

  • You’ll be able to speak really good English by the end of the year.

3.2, 现在完成时

  • We’ve been unable to complete the project within the specified budget.
  • How long has your little boy been able to read?

3.3 过去完成时

  • He was given a detention because he hadn’t been able tofinish his homework.

4,尽管can和can’t 一般不用于将来,但可以用can来表示将来可能的行为。

  • I can join you at the meeting, but I can’t stay very long.

5, Can 和be able to的使用方法汇总表


肯定句
否定句(或否定含义) 疑问句
现在时 can work

am able towork

can’t work

am not able to work

am unable towork

Can I work?

Am (un)able to work?

过去时 could work

was able towork

couldn’t work

was not able to work

was unable to work

Could I work?

Was (un)able to work?

将来时 will / shall be able towork won’t / shan’t be able to work

will / shall be unable towork

Will / shall be (un)able towork?
现在完成时 have been able to work haven’t been able to work

have been unable to work

Have been (un)able towork?
过去完成时 had been able to work hadn’t been able to work

had been unable to work

Had been (un)able towork?

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