Chapter 8 情态动词
8.8 基本用法（三）：过去的能力
8.8 基本用法（三）：过去的能力
2016年6月16日，上海迪士尼乐园（Disneyland）正式开放，这是世界上第6个迪士尼主题公园。相信迪士尼乐园是很多人梦寐以求的地方，我们可以这样畅想：
1 I hope I can go to Disneyland one day. 我希望将来有一天我能去迪士尼乐园。
如果是“今天我能去迪士尼乐园”，用英语可以这么说：
2 Today I can go to Disneyland.
或者说：Today I am able to go to Disneyland.
在8.6节中讲过，can强调的是“潜在的可能性”，而不是真正去实施，所以这句话其实是说“尽管理论上有条件去，但实际上我可能去，也可能不去”。
我们现在把时间改为“昨天”，来表达一个确定的事实，即“我昨天终于能够去迪士尼乐园”，这时要怎么说呢？
也许有读者认为，只要把can改成过去式could就可以了。比如：
Yesterday I could go to Disneyland. *
这种说法是不正确的，或者说在英语中不存在上面这样的句子。如果一个英语为母语的人听到了这个句子，他或许还会进一步问你“昨天你到底是去了还是没有去？”。如果是去了，他会让你说：
3 Yesterday I was able to go to Disneyland.
如果是要表达“我昨天本来是可以去，但结果没有去成”这样的虚拟意思，则要说成：
Yesterday I could have gone to Disneyland.
所以，在英语中不存在“Yesterday I could go to Disneyland.”这样的句子。
看到这里，一定有读者要问换成过去时态后，用could为什么就不正确呢？为什么只能用was able to？
这个问题涉及could和was able to在表达“过去的能力（past ability）”时的区别。
看到can/could，读者的第一反应可能就是“能够”的意思，但其实这样并没有真正掌握can/could的核心意思。比如汉语里完全可以说“昨天能够怎样怎样”，但在英语里却不能说“Yesterday I could…”这样的句子。在8.6节中强调过，can/could的核心意思是表示一种“潜能”（The core concept of CAN is about“potential”.），强调的是“潜在的可能性”，而不一定真正去实施。具体来说就是表示因为具备某些特点或条件，某人能够完成某件事或某事是可能存在的，而并不是强调何时或怎样实施这种潜在的行为。比如下面短文中的can就表示这种“潜在的可能”：
4 When Disney began designing its newest kingdom in Hong Kong, planners decided Mickey’s magic wasn’t enough for success. The park needed an extra boost from“feng shui”. In Hong Kong,“feng shui”has played a large part in the park’s design. A master moved its main gate so it was facing the right direction, put a bend in its walkway so that“qi”or energy does not flow into the South China Sea and does not have the unlucky number“four”in its elevators. It’s a tricky business, but few dare to ignore it in Hong Kong. Many believe bad feng shui can cause financial ruin, and Disney wasn’t about to risk it, Tom Morris, a chief designer at Hong Kong Disneyland, said.
妙语点睛 该短文讲到了美国迪士尼集团为了融入中国的本土文化（fit into the local culture），在设计香港迪士尼乐园时充分考虑了中国的“风水”文化。比如在修建香港迪士尼乐园新的入口时，迪士尼集团的管理层决定把正门方位调整12度。之所以这样做，是因为他们咨询了一位中国的风水大师。另外，从火车站到大门的走道上，迪士尼还专门设计了一个拐弯，以确保“气”不会流进南海里。在香港迪士尼乐园，每建好一座建筑，就会举行焚香仪式；同时还专门挑选了被认为是黄道吉日的9月12日作为首次开放的时间。根据我们的风水文化，“风水不好，就有可能造成财务亏损（bad feng shui can cause financial ruin）”，因此迪士尼集团也不敢冒这个险而甘愿向风水“折腰”。这里的can显然是表示一种“潜在的可能性”。
现在我们回头看本章开头的两个例句：
1） I hope I can go to Disneyland one day.
2） Today I can go to Disneyland.
“将来能够”或者是“今天能够”去迪士尼乐园，强调的都是一种“潜在的可能性”，而不一定真正去实施。也就是说，尽管理论上我可以去迪士尼乐园，但实际上我可能去，也可能不去。但如果我们谈一个具体的过去的事件，如“昨天能够去迪士尼乐园”，则表达一个确定的事实，没有“潜在的可能”的意思了，这就违背了can表示“潜能”这一核心意思。故不能说出“Yesterday I could go to Disneyland. *”这样的句子。
所以，从“将来能够”或“今天能够”变为“昨天能够”，改变的不仅是时态问题，更重要的是其中can所蕴含的“潜在的可能性”这一核心思维。当用can谈将来的事件或现在的事件时，这种“潜在的可能性”是一直存在的，以至于使我们忽略了can的这一重要思维。但是，若谈论过去的事件时，这种“潜在的可能性”有可能（但不是必然）会丧失。这个问题涉及在表达“过去的能力”时，could和was able to的区别。
简单来说，二者的区别是：could表示“过去的一般能力”，was able to表示“过去的具体能力”。具体地说，所谓“过去的一般能力”就是指在过去有能力想做某件事就随时可以去做，但并不说明真正实施了这个行为，即强调的是一种“潜能”，而不是某一次具体的过去行为（When used to denote past ability, COULD does not refer to a single instance of ability on a particular occasion, but rather, it signifies an ability in a very general sense.）。例如：
5 I could run after a bus and catch it twenty years ago, but I can’t do that now.
妙语点睛 这里只是说明我过去有“追上汽车”的能力，而并没有强调我真的有过“追车”这个行为，即表示的是一种“潜能”或“一般能力”，所以用could来表示“潜在的可能”。这里不能用can，因为can表示的是现在或将来。
所谓过去的“具体的能力”，即表示主语在过去的某个特定场合所实施的具体行动，此时没有“潜在的可能性”，所以不能用could，而要用was/were able to，表示“成功地做成了某事”。因此was/were able to do可用succeeded in doing或managed to do替换（The successful demonstration of ability on a particular past occasion is expressed by means of be able to, manage to do, succeed in, etc.）。例如：
6 I ran after the bus yesterday and was able to catch it.
妙语点睛 这里用was able to表示的正是过去的一次具体的行为，说明具体实施了“追车”这一行为，而且成功地追上了，即表示“具体的能力”，而不是过去的“潜能”。
下面是迪士尼乐园创始人沃特·迪士尼（Walt Disney）先生在谈到迪士尼乐园的设想时说的话：
7 I think what I want Disneyland to be most of all is a happy place, a place where adults and children can experience together some of the wonders of life, of adventure, and feel better because of it. 我想，我希望迪士尼乐园首先要成为一个充满快乐的地方，无论是成年人还是孩子，都能在这里体验到生命和探险的神奇，并因此而有更美好的感受。
我们现在可以用过去时来转述他的话：
Walt Disney revealed that his Disneyland Park would be an environment where parents and children could have fun together and could experience some of the wonders of life and adventure. 沃特·迪士尼说，他的迪士尼乐园将会是一个父母与孩子能找到快乐，能体验生命和探险的神奇的地方。
两个句子都不是表示一次“实际的行动”，而是传达一种“潜在的可能”，所以用can/could。如果是谈过去一次具体的活动，则要用be able to。比如回忆自己游览迪士尼乐园的经历：
8 I was able to experience the wonders of life and adventure in Disneyland last week.
我们再来看下面这篇短文：
9 Volcanoes
Haroun Tazieff, the Polish scientist, has spent his lifetime studying active volcanoes and deep caves in all parts of the world. In 1948, he went to Lake Kivu in the Congo to observe a new volcano which he later named Kituro. Tazieff was able to set up his camp very close to the volcano while it was erupting violently. Though he managed to take a number of brilliant photographs, he could not stay near the volcano for very long. He noticed that a river of liquid rock was coming towards him. It threatened to surround him completely, but Tazieff managed to escape just in time. He waited until the volcano became quiet and he was able to return two days later. This time, he managed to climb into the mouth of Kituro so that he could take photographs and measure temperatures. Tazieff has often risked his life in this way. He has been able to tell us more about active volcanoes than any man alive.
妙语点睛 我们看到，这里was able to与managed to进行了多次互换使用。其中还有could表示过去的一般能力。
综上所述，could同can一样，表示的是一种“潜能”或者说“过去的一般能力”，而不是“实际行动”；was/were able to则更多的是用来表示过去的“实际行动”或者说“具体的能力”。但注意，也可以用was/were able to表示“潜能”，但不如could常用。请再看更多的例句：
一、表示过去的“潜能”
10 He could/was able to pull down a bull and acknowledged as a man with super strength.
妙语点睛 这里只是说他“曾经能够”，并没有具体说是哪次活动，所以是“潜能”，不是“实际行动”。
11 I could/was able to recite several poems when I was 3 years of age. 我3岁时就能背诵好几首诗歌。
12 Fred could/was able to speak Russian when he was 6 years old. 弗雷德6岁就能说俄语。
13 In those days few workers could support their families. 那时很少有工人能够养家糊口。
二、表示过去的“实际行动”（均不能用could）
14 They were able to get tickets to the Rolling Stones concert last week. 上周他们搞到了滚石乐队演唱会的票。
15 How were you able to convince him to come to the exhibition last week? 上周你是怎么说服他去看展览的？
16 With the aid of the wood, he was able to swim across the river. 借助这块木头，他就能游过河去了。
17 I applied everywhere and finally I was able to get a good job. 我四处应聘，终于找到了一份不错的工作。
18 He hurried to the station, and he was able to catch the train. 他赶到车站，赶上了火车。
19 The fire spread through the building quickly but everybody was able to escape.
20 The two boys tried many ways to catch that sly fox and were able to do so at last.
21 Although the pilot was badly hurt he was able to explain what had happened.
22 Tom has started an exercise program. He was able to run two miles yesterday without stopping or slowing down.
23 He didn’t agree with me at first but I was able to persuade him. 起初他并不同意我的意见，但最终我成功说服了他。
对于某些句子，既可以用could，又可以用was/were able to，此时的含义是不同的。比如：
24 1） I could repair the old car.
2） I was able to repair the old car.
妙语点睛 在例句1）中，用could表达的是过去的一般能力，即表示“我过去是能够修理旧汽车的”，这里是泛指任何一辆旧汽车。在例句2）中，用was able to表达的是过去的具体能力，即表示“我终于把那辆旧汽车修理好了”，这里是具体指某一辆特定的旧汽车。
2） 我终于把那辆旧汽车修理好了。
我们再来看下面这篇短文：
25 Over the South Pole
In 1929, three years after his flight over the North Pole, the American explorer, R. E. Byrd, successfully flew over the South Pole for the first time. Though, at first, Byrd and his men were able to take a great many photographs of the mountains that lay below, they soon ran into serious trouble. At one point, it seemed certain that their plane would crash. It could only get over the mountains if it rose to 10,000 feet. Byrd at once ordered his men to throw out two heavy food sacks. The plane was then able to rise and it cleared the mountains by 400 feet. Byrd now knew that he would be able to reach the South Pole which was 300 miles away, for there were no more mountains in sight. The aircraft was able to fly over the endless white plains without difficulty.
有趣的是，上述could和was/were able to的区别仅限于肯定句中，在否定句中could 和was/were able to可以互换使用，没有区别。比如可以说：
26 I ran after the bus yesterday, but wasn’t able to/couldn’t catch it. 昨天我追赶了公共汽车，但是没赶上。
27 I applied everywhere and I wasn’t able to/couldn’t get any good job. 我四处应聘，但是没能找到好工作。
28 The fire spread through the building quickly and people weren’t able to/couldn’t escape.
29 Though he managed to take a number of brilliant photographs, he could not stay near the volcano for very long.
尽管这里是表示过去的具体场合，但依然用了could，因为有否定的not，即couldn’t表示过去具体的能力。
思维总结
首先，在can/could表示“能力”时，二者均表示“潜能”或者说“一般能力”。其中，can表示将来或现在的一般能力，could表示过去的一般能力。
其次，could表示“过去的一般能力”，不表示“过去具体的能力”；was/were able to既可以表示“过去的一般能力”，也可以表示“过去具体的能力”。
最后，结合8.7节中讨论的“可能”的含义，我们发现，虽然could不能谈“过去具体的能力”，但可以表示“具体的可能”（如“He could be sick.”表示现在或将来的具体可能，或“He could have been sick.”表示过去的具体可能）。所以，could可以用来谈论“具体的可能”“理论上的可能”，以及“过去的一般能力”，但不能谈“过去具体的能力”。另外值得注意的是，could表示“推测”时，本身不能表示“过去”，而是用could have done来表示过去的可能。但could表示“能力”时，本身就表示“过去”，即“过去的一般能力”。
最后，在否定句中，couldn’t和wasn’t/weren’t able to没有区别，即couldn’t可以谈过去具体的能力，表示在过去某一特定场合“未能”完成某事。
思维训练 8.8 Key
一、请在合适的地方填上could或couldn’t或was/were able to。
1. I applied everywhere and finally I ______ get a good job.
2. Although the pilot was badly hurt he ______ explain what had happened.
3. Tom has started an exercise program. He ______ run two miles yesterday without stopping or slowing down.
4. I ______ run two miles without stopping or slowing down when I was in my 20s.
5. He didn’t agree with me at first but I ______ persuade him.
6. Fred ______ speak Russian when he was six years old.
7. They ______ get tickets to the Rolling Stones concert last week.
8. After waiting for an hour, I finally ______ see the doctor.
9. I ______ see anything in all that smoke. But then a fireman emerged from the darkness and saved my life.
10. I tried to persuade Grace to come with us, but I ______ convince her.
11. A: Did you see the exhibit at the art center?
B: I sure did. And I ______ make heads or tails of it.
12. A: I lived with my sister this summer and didn’t have to pay rent. So I ______ save most of my salary.
B: Not me. The more I earned, the more I spent.
13. They didn’t want to come with us at first but we ______ persuade them.
14. Jack was an excellent tennis player. He ______ beat anybody.
15. Jack and John had a game of tennis yesterday. John played very well but in the end Jack ______ beat him.
16. I looked everywhere for the book but I ______ find it.
17. I looked everywhere for the book and finally I ______ find it.
18. Sue wasn’t at home when I phoned but I ______ contact her at her office.
19. My mother loved music. She ______ play the piano very well.
20. A girl fell into the river but fortunately we ______ rescue her.
21. I had forgotten to bring my camera so I ______ take any photographs.
22. Although I forgot to bring my camera that day, I ______ take some nice photographs with John’s camera.
23. When I worked as a secretary, I ______ type 60 words a minute without making a mistake. My typing skills aren’t nearly as good now.
24. Yesterday I typed these reports for my boss. I don’t type very well, but I ______ finish the reports without making too many mistakes.
25. When I ran into Mr. Smith yesterday, I ______ recognize him even though I hadn’t seen him for years.
26. At the sale yesterday, I ______ get this shirt at half price. Quite a bargain, don’t you think?
27. My grandfather was a merchant all his life. He knew how to make a sale by using psychology. He ______ convince anyone to buy anything, whether they needed it or not.
28. Volcanoes
Haroun Tazieff, the Polish scientist, has spent his lifetime studying active volcanoes and deep caves in all parts of the world. In 1948, he went to Lake Kivu in the Congo to observe a new volcano which he later named Kituro. Tazieff ______ set up his camp very close to the volcano while it was erupting violently. Though he ______ take a number of brilliant photographs, he ______ stay near the volcano for very long. He noticed that a river of liquid rock was coming towards him. It threatened to surround him completely, but Tazieff ______ escape just in time. He waited until the volcano became quiet and he ______ return two days later. This time, he ______ climb into the mouth of Kituro so that he ______ take photographs and measure temperatures. Tazieff has often risked his life in this way. He has been able to tell us more about active volcanoes than any man alive.
二、请翻译下列句子，并比较两句含义的差别。
29. I was able to go to the library last night.
30. I could have gone to the library last night.