“be able to”

be able to + 动词原形——能够做某事，有能力做某事。随时态变化的只有 be（am / is / are, was / were, will be, have been…）；able to 和后面的动词保持不变。

简略回答重复 be / will / have：Yes, I was. / No, I won't. / No, I haven't. 否定也可以用 unable to（稍正式）：I'm unable to attend the meeting.

💡Able 是形容词（和 tired、happy 一样），所以前面一定要有 be——就像你说 I am tired 一样。中文说“我能够……”不需要别的词，所以学习者常写成 “I able to…” 或 “I don't able to…”。正确的形式是 I'm able to… / I'm not able to…

正如“‘can / could’ 表示能力”一课所讲，can 只有两种形式：can 和 could。其他情况都要用 be able to 代替 can。

1. 将来——will be able to / won't be able to

• After this course, you'll be able to order food in English.

  上完这门课，你就能用英语点餐了。

• Sorry, I won't be able to make it on Saturday.

  抱歉，星期六我去不了了。

如果是现在就安排或决定将来的事，用 can 仍然很自然：I can see you tomorrow at ten. 但如果这种能力现在还没有，要以后才会有（上完课、身体好了、有了车……），就用 will be able to。

2. 完成时——have / has been able to

• I haven't been able to reach him all day.

  我一整天都联系不上他。

• Since she got glasses, she's been able to read the board clearly.

  她配了眼镜以后，就能看清黑板了。

3. 在另一个情态动词后面——might / may / should / must + be able to（两个情态动词不能连用）

• Ask Minh — he might be able to fix it.

  问问阿明吧——他也许能修好。（不说：might can）

• Nurses must be able to stay calm.

  护士必须能够保持冷静。

4. 在 to 后面和 -ing 形式中——to be able to, being able to

• I want to be able to talk to my customers in English.

  我希望能用英语和客户交流。

• Being able to drive makes life much easier.

  会开车让生活方便多了。

used to 也一样：My grandpa used to be able to walk for hours.（他以前能走那么久——现在不行了。）

在现在时中两种说法都对，但口语里 can 常用得多。Am / is / are able to 听起来更正式——常见于邮件和通知——或者用来强调某人在情况变化后现在能够做某事了。

• I can speak a little Japanese.

  我会说一点日语。（日常说法）

• Customers are able to change their booking online.

  顾客可以在网上更改预订。（通知 / 正式）

• After the operation, Grandpa is able to walk again.

  手术后，爷爷又能走路了。（强调：他现在能走了）

• Minh could run really fast when he was a kid.

  阿明小时候跑得特别快。（一般能力）

• Yesterday Minh managed to catch the last train.

  昨天阿明赶上了末班火车。（某一次；不说：could catch）

• It was a tough match, but we were able to win.

  比赛很艰难，但我们还是赢了。

• The box was heavy, but I managed to carry it upstairs.

  箱子很重，但我还是把它搬上了楼。

Managed to + 动词原形 强调这件事很难、费了一番力气。否定：didn't manage to（= couldn't）。

例外：和 see、hear、smell、taste、feel、understand、remember 连用时，表示某一次也可以用 could：When I opened the door, I could smell smoke.

💡快速判断：如果句子里能加上 “in the end”（最后）或 “on that day”（那天），就是某一次 → was able to / managed to。如果你想说的是 “那时候我会……” → could。

• ✗I able to swim.

  ✓I'm able to swim.

  Able 是形容词——需要 be。

• ✗We weren't able find the hotel.

  ✓We weren't able to find the hotel.

  able 后面总是跟 to。

• ✗I don't able to come.

  ✓I'm not able to come.

  否定用 be + not，不用 don't。

• ✗I hope I can be able to visit you.

  ✓I hope I'll be able to visit you.

  can 和 be able to 不能一起用。

• ✗The bus was late, but I could arrive on time.

  ✓The bus was late, but I managed to arrive on time.

  某一次具体的事 → 用 managed to / was able to，不用 could。

• ✗She has able to drive since last year.

  ✓She has been able to drive since last year.

  完成时：has been able to。