语法

情态动词 may / might / can / could (Permission & Possibility)

语法点：情态动词 may / might / can / could (Permission & Possibility)

may / might / can / could 是四个常用情态动词，后面一律接动词原形，没有人称和数的变化。它们主要表达两种意思：一是“可能性”，即说话人对事情的推测，can 表示一般或理论上的可能，may 表示有可能，might 和 could 语气更不确定；二是“允许”和“能力”，may 用于正式地请求或给予许可，can 表示能力或口语中的许可，could 是 can 的过去式，也可用于更客气的请求。在间接引语中，may 常变为 might，can 变为 could。本课里 balloons can be a great danger 是一般可能，someone might be spying 是不确定的推测，could make out / could not arrest 则是过去的能力。

结构

情态动词	可能性	允许 / 能力	例句
can	一般可能（理论上会发生）	有能力做；口语许可	Balloons can be a great danger to aircraft.
could	较小的可能；过去的可能	过去的能力；客气请求	He could make out three men in a basket.
may	有可能（约一半把握）	正式许可	Someone may be spying on the station.
might	可能性更小；may 的过去式	非常客气的请求	He said that someone might be spying on the station.

否定：cannot / can't, could not / couldn't, may not, might not。疑问：Can / Could / May + 主语 + 动词原形? 表示“正在进行的可能”用 may / might + be + 动词-ing。

课文中的例句

[句 3] …because balloons can be a great danger to aircraft. — can 表示一般性的可能：气球“可能会”对飞机构成危险
[句 4] He said that someone might be spying on the station… — might be spying 表示不太确定的推测，且因间接引语从 may 变为 might
[句 6] He could make out three men in a basket under it… — could 是 can 的过去式，表示当时有能力看清
[句 9] The police were called in, but they could not arrest anyone… — could not 表示过去没有能力（没有理由）逮捕任何人
[句 2] …but no one there was able to explain the mystery. — was able to 与 could 意思相近，表示过去的能力

补充例句

A balloon may land near the airfield this afternoon. — 今天下午一个气球可能会降落在机场附近。
Could you explain the mystery to the officer? — 你能向那位军官解释一下这个谜吗？
You may take photographs here, but you can't fly a balloon over the station. — 你可以在这里拍照，但不能在基地上空放气球。

易错点

❌ Balloons can to be a great danger. → ✅ Balloons can be a great danger. — 情态动词后接动词原形，不加 to。
❌ Someone might spies on the station. → ✅ Someone might spy on the station. — might 后面的动词不能加 s。
❌ He said that someone may spying on the station. → ✅ He said that someone might be spying on the station. — 表示可能正在进行要用 might be + 动词-ing，间接引语中 may 也要变成 might。
❌ The police didn't could arrest anyone. → ✅ The police could not arrest anyone. — 情态动词自己构成否定，不需要 didn't。

逐句语法分析 · 10 句

1A pilot noticed a balloon which seemed to be making for a Royal Air Force station nearby.
一位飞行员注意到一只气球似乎正朝附近的一个皇家空军基地飞去。
一般过去时 (Simple Past) · 主语 + 动词过去式 + 宾语 + which 定语从句 (seemed to be doing)
- which seemed to be making for 是定语从句，修饰 balloon
- seem to be doing 表示“看起来正在……”
- make for 意为“朝……前进”
主句 noticed 是过去式，定语从句用 seemed to be making 描述气球看起来正飞向基地。
2He informed the station at once, but no one there was able to explain the mystery.
他立即通知了基地，但那里没有人能解释这个谜。
一般过去时 (Simple Past) · 主语 + 动词过去式 + 宾语 + at once, but + 主语 + was able to + 动词原形
- at once 表示“立刻”
- no one … was able to 相当于 could not，表示过去没有能力
- no one 作主语视为单数，所以用 was
was able to explain 表示过去的能力，与本课 could 用法互为替换。
3The officer in the control tower was very angry when he heard the news, because balloons can be a great danger to aircraft.
控制塔的军官听到这个消息时非常生气，因为气球对飞机可能构成很大的危险。
一般过去时 (Simple Past) + 情态动词 can · 主语 + was + 形容词 + when 时间从句, because 原因从句 (主语 + can be + 表语)
- can be a great danger 表示一般性的可能
- 原因从句用一般现在时，因为说的是普遍事实
- a danger to 表示“对……的危险”
主句是过去时，because 从句的 can 表示气球随时都可能危及飞机这一普遍情况。
4He said that someone might be spying on the station and the pilot was ordered to keep track of the strange object.
他说可能有人在侦察这个基地，飞行员奉命跟踪这个奇怪的物体。
一般过去时 (Simple Past) + 情态动词 might + 进行式 / 被动语态 · 主语 + said that + 宾语从句 (might be + 动词-ing) and + 主语 + was ordered to + 动词原形
- might be spying 表示对正在进行的动作的不确定推测
- 间接引语中 may 变为 might
- was ordered to keep track of 是被动语态，意为“被命令跟踪”
might be spying 是本课核心用法：推测某人可能正在侦察；后半句为被动语态。
5The pilot managed to circle the balloon for some time.
飞行员设法绕着气球盘旋了一段时间。
一般过去时 (Simple Past) · 主语 + managed to + 动词原形 + 宾语 + 时间状语
- managed to do 表示“设法做成了”，强调成功
- circle 作动词意为“绕……飞行”
- for some time 表示持续了一段时间
managed to circle 表示飞行员成功地绕气球飞了一阵，比 could 更强调结果。
6He could make out three men in a basket under it and one of them was holding a pair of binoculars.
他可以辨认出气球下面的吊篮里有三个人，其中一人拿着一副望远镜。
一般过去时 (Simple Past) + 情态动词 could + 过去进行时 (Past Continuous) · 主语 + could + 动词原形 + 宾语 + 地点状语 and + 主语 + was holding + 宾语
- could make out 表示过去有能力辨认出
- make out 意为“看清、辨认出”
- was holding 过去进行时描述当时正在进行的动作
could 作为 can 的过去式表示当时能看清；was holding 描述其中一人正拿着望远镜。
7When the balloon was over the station, the pilot saw one of the men taking photographs.
当气球飞越基地上空时，飞行员看见其中一个人在拍照。
一般过去时 (Simple Past) · When 时间从句 + 主语 + saw + 宾语 + 动词-ing
- see someone doing 表示看见某人正在做某事
- one of the men 后接 taking，突出动作正在进行
- when 从句和主句都用一般过去时
saw … taking photographs 是感官动词 + 宾语 + 现在分词，表示看到动作正在进行。
8Soon afterwards, the balloon began to descend and it landed near an airfield.
不久之后，气球开始下降，降落在一个机场附近。
一般过去时 (Simple Past) · 时间状语 + 主语 + began to + 动词原形 and + 主语 + 动词过去式 + 地点状语
- began to descend 表示动作的开始
- soon afterwards 意为“不久之后”
- landed near 用 near 表示“在……附近”
两个并列的过去式动作按时间顺序叙述气球下降并着陆。
9The police were called in, but they could not arrest anyone, for the basket contained two Members of Parliament and the Commanding Officer of the station!
警察被叫来了，但他们谁也不能逮捕，因为吊篮里坐着两位议员和这个基地的指挥官！
一般过去时被动 (Simple Past Passive) + 情态动词 could not · 主语 + were called in, but + 主语 + could not + 动词原形 + 宾语, for 原因分句
- were called in 是被动语态，call in 意为“召来”
- could not arrest 表示过去没有能力或理由逮捕
- for 在这里是连词，引出原因
could not 作为本课要点，表示警察当时无法逮捕任何人；for 说明原因。
10As the Commanding Officer explained later, one half of the station did not know what the other half was doing!
正如指挥官后来解释的那样，基地的一半人不知道另一半人在做什么！
一般过去时 (Simple Past) + 过去进行时 (Past Continuous) · As 方式从句 + 主语 + did not know + what 宾语从句 (was doing)
- as … explained later 意为“正如……后来所解释的”
- did not know 是一般过去时的否定
- what the other half was doing 是宾语从句，用过去进行时
宾语从句 what … was doing 用陈述语序，过去进行时描述当时正在做的事。

练习 · 44 题

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选择正确的答案
1. The officer was angry because balloons ____ a great danger to aircraft.
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2. He said that someone ____ on the station.
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3. The pilot ____ make out three men in a basket under the balloon.
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4. The police were called in, but they ____ arrest anyone.
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5. ____ I take a photograph of the station, sir?
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6. He said, 'Someone may be spying on the station.' → He said that someone ____ be spying on the station.
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7. The balloon ____ land near the airfield; nobody is sure.
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8. No one there ____ explain the mystery.
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9. The pilot was ordered to ____ of the strange object.
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10. The pilot saw one of the men ____ photographs.