Chapter 5 动词分类（一）：实义动词与（情态）助动词
5.3 情态助动词（modal verb）
5.3 情态助动词（modal verb）
情态动词的特点：
从词义的角度来看，情态动词有别于助动词。情态动词有其自身的词汇意义，如用来表示可能、建议、愿望、必要、允许、能力、怀疑等等，以表示说话者对某种行为或状态的看法或态度。
从在谓语中的作用这一角度来看，与助动词一样，情态动词在句中不能单独作句子的谓语，而必须和实义动词一起构成复合谓语。
英文中的情态动词主要有下列10个：
can/could, may/might, shall/should, will/would, must和had better。
另外还有一些与上述情态动词有关的短语动词：
be able to（与can类似）
be going to（与will类似）
ought to, be supposed to（与should类似）
have to, have got to（与must类似）
此外，need和dare既可以用作情态动词，也可以用作实义动词。
关于情态动词的详细用法，由于较为复杂，我们安排在《英语语法新思维中级教程——通悟语法》中详尽讨论，故在此不再赘述。
我们现在通过下面这篇幽默短文，来总结一下上面讨论的内容。我们来判断下列各句中的谓语动词哪些是实义动词、助动词或情态动词。
Two men were standing at a bar. One man turned to the other and said, “I'll bet you $100 that I can bite（咬） my left eye.” The wager（赌注） was accepted, and the man popped（突然挖出） out his glass eye and bit（bite的过去式） it.
“Now,” he said, “I'll give you a chance to win your money back. I'll bet you another $100 that I can bite my right eye.” “He can't have two glass eyes,” thought the other man, and he plunked（重重甩下） down his money.
Then the first man took out his false teeth and bit his right eye.
我们现在逐句分析其中各句的谓语构成。
1） Two men were standing at a bar.
妙语点睛 该句的谓语是were standing，其中were是助动词，没有词义，只是用来帮助构成过去进行时态；standing是实义动词。由此看到，助动词不能单独作谓语，必须与实义动词一起构成谓语。
2） One man turned to the other and said, ...
妙语点睛 该句有两个并列谓语：turned和said，都是实义动词。由此看出，实义动词能单独作谓语。
3） I'll bet you $100 that I can bite my left eye.
妙语点睛 该句是一个主从复合句，所以有两个谓语：主句的谓语will bet和从句的谓语can bite。在主句的谓语中，’ll bet是will bet的缩写，这里will是情态动词，词义可以解释为“愿意”；bet是实义动词。在从句的谓语中，can是情态动词，词义可以解释为“能够”；bite是实义动词。由此看到，情态动词具有特定的词义，但与助动词一样不能单独作谓语，必须与实义动词一起构成谓语。
4） The wager was accepted, ...
妙语点睛 该句的谓语是was accepted，其中was是助动词，没有词义，只是用来帮助构成被动语态；accepted是实义动词。由此看到，助动词不能单独作谓语，必须与实义动词一起构成谓语。
5） ...and the man popped out his glass eye and bit it.
妙语点睛 该句有两个并列谓语：popped out和bit，都是实义动词。由此看出，实义动词能单独作谓语。
6） “Now,” he said, “I'll give you a chance to win your money back.
妙语点睛 这里有一个直接引语。引语外的句子的谓语said是实义动词。引语中的句子的谓语是’ll give，是will give的缩写。这里的will是情态动词，词义可以解释为“愿意”；give是实义动词。由此看出，情态动词有特定的词义，但与助动词一样不能单独作谓语，必须与实义动词一起构成谓语。
7） I'll bet you another $100 that I can bite my right eye.
妙语点睛 该句是一个主从复合句，所以有两个谓语：主句的谓语will bet和从句的谓语can bite。在主句的谓语中，’ll bet是will bet的缩写，这里will是情态动词，词义可以解释为“愿意”；bet是实义动词。在从句的谓语中，can是情态动词，词义可以解释为“能够”；bite是实义动词。由此看出，情态动词具有特定的词义，但与助动词一样不能单独作谓语，必须与实义动词一起构成谓语。
8） He can't have two glass eyes, ...
妙语点睛 该句的谓语是can't have，其中can't是情态助动词，词义可以解释为“能够”；have是实义动词，表示“有”的意思。注意这里的have不是助动词。
9） ...thought the other man, ...
妙语点睛 该句是一个倒装句，谓语是thought这个实义动词，主语是the other man。
10） ...and he plunked down his money.
妙语点睛 该句的谓语是plunked，是实义动词。由此看出，实义动词能单独作谓语。
11） Then the first man took out his false teeth and bit his right eye.
妙语点睛 该句有两个并列谓语：took out和bit，都是实义动词。由此看出，实义动词能单独作谓语。
思维总结
英文中的动词有各种分类，在这里，我们只是根据动词的词义和它在谓语中的作用所作出的动词分类，而这也是英文中的动词最为基本的分类。这种动词分类方式主要是为了下面讨论英语句子谓语变化打下基础。所以要求读者熟练掌握，学会辨别。
找出下列句子中的实义动词、助动词或情态动词。
1. Studying English takes time.
2. The first step is always the hardest.
3. The library was built last year.
4. I can't stand the heat.
5. You can leave the door open.
6. He speaks English well.
7. That can save you a lot of time.
8. I will find you a good teacher.
9. I find you a good teacher.
10. She will make him a good wife.
11. I often do my homework at the school, but yesterday I did it at home. Jim doesn't do that. He likes doing his homework at home.
12. I have two brothers. One brother has been out of school for many years. Now he is working in a dot-com company（网络公司）. He is married and has his own family. The other brother is now at college and hasn't graduated yet. He has a girlfriend and they have known each other for 2 years.