这是什么？
Can、can’t、could 和 couldn’t 是情态动词。
它们用于谈论：
- 现在的能力
- 过去的能力
- 许可
- 请求
- 可能性
Can 是肯定形式。
- I can swim.
Can’t 是 cannot 的缩略形式。
- I can’t drive.
Could 常用于过去的能力或礼貌的请求。
- She could read when she was four.
- Could you help me?
Couldn’t 是 could not 的缩略形式。
- We couldn’t find the address.
何时使用
用 can 表示现在的能力。
- He can speak English.
- I can cook.
当某人不能做某事时，用 can’t。
- She can’t swim.
- We can’t come today.
用 can 来请求或给予许可。
- Can I use your phone?
- You can leave early.
用 could 表示过去的一般能力。
- I could run fast when I was younger.
- They could speak French as children.
用 couldn’t 表示过去缺乏能力或未成功的情况。
- He couldn’t read the sign.
- We couldn’t open the door.
用 can 或 could 提出请求。
- Can you close the window?
- Could you close the window?
在请求中，could 通常比 can 更礼貌。
结构
在 can、can’t、could 和 couldn’t 之后使用动词原形。
| 形式 | 结构 | 示例 |
|---|---|---|
| 现在肯定 | subject + can + 动词原形 | She can drive. |
| 现在否定 | subject + can’t + 动词原形 | She can’t drive. |
| 过去肯定 | subject + could + 动词原形 | She could drive at eighteen. |
| 过去否定 | subject + couldn’t + 动词原形 | She couldn’t drive last year. |
所有主语的形式都相同。
- I can swim.
- He can swim.
- They can swim.
不要在 he、she 或 it 后面加 -s。
疑问句
使用：
Can/Could + 主语 + 动词原形？
| 疑问类型 | 示例 |
|---|---|
| 现在能力 | Can you swim? |
| 许可 | Can I sit here? |
| 请求 | Can you help me? |
| 礼貌请求 | Could you help me? |
| 过去能力 | Could she read at five? |
简短回答
- Can you drive? — Yes, I can.
- Can he come? — No, he can’t.
- Could they swim? — Yes, they could.
- Could she open it? — No, she couldn’t.
示例
- I can speak a little Spanish.
- She can’t come to work today.
- Can you help me with this box?
- Can I open the window?
- You can use my computer.
- He could swim when he was five.
- We couldn’t find a taxi last night.
- Could you speak more slowly, please?
- They could not hear the announcement.
- My brother can cook very well.
例外情况
用 could 表示过去的一般能力。
- She could play the piano when she was young.
对于过去某个具体的成功动作，was able to 通常更自然。
- We were able to fix the problem yesterday.
然而，couldn’t 用于过去某个具体的不成功动作是自然的。
- We couldn’t fix the problem yesterday.
Cannot 写作一个词。
- 正确：cannot
- 错误：can not
can not 这种形式只有在 not 属于另一个短语时才可能使用，但这种用法不常见。
常见错误
-
错误： She cans swim. 正确： She can swim. 解释： 不要在情态动词后加 -s。
-
错误： I can to drive. 正确： I can drive. 解释： 在 can 之后使用不带 to 的动词原形。
-
错误： He could speaks English. 正确： He could speak English. 解释： 在 could 之后使用动词原形。
-
错误： Do you can help me? 正确： Can you help me? 解释： 在带有 can 的疑问句中不要使用 do。
-
错误： I don’t can swim. 正确： I can’t swim. 解释： 使用 can’t，而不是 don’t can。
-
错误： She could to read at four. 正确： She could read at four. 解释： 在 could 之后不要使用 to。
-
错误： Can you helped me? 正确： Can you help me? 解释： 在 can 之后使用动词原形。
-
错误： I couldn’t found my keys. 正确： I couldn’t find my keys. 解释： 在 couldn’t 之后使用动词原形。