1、助動詞與情態(tài)動詞 動詞表示動作形態(tài)，但英語里有些動詞并不表示動作形態(tài)，而是協(xié)助主動詞表示時態(tài)（tenses）或語態(tài)（voices）。這些動詞如“ do, is, have”等，叫助動詞（auxiliary verbs）。另外有些動詞如“can, will, may, must”等，則可協(xié)助動詞表示語氣或情態(tài)，叫情態(tài)動詞（modal verbs）。  助動詞和情態(tài)動詞都是特殊動詞，非常有用。沒有了它們，疑問句不能成立，否定句也難形成。沒有了“have, has, had”完成時態(tài)（perfect tenses）無法存在；沒有了“be, is, are, am, been, w

2、as, were, being”，何來被動語態(tài)（the passive voice）？請看下列例子，就知道梗概了：   -What do you do every day? -I teach every day.   -Can they speak English? -Yes, they can.   -Will he do it? -No, he won't.   -John lived here before. -John did not live here before.   -Betty has completed her wo

3、rk on time. -She is really good.   -After I had eaten my breakfast, I went to office. -How about Nancy? Did she do the same?   -Jason is writing a new book. -A new book is being written by Sam, too.   -The cat caught a rat. -A rat was caught by a cat.  此外，助動詞和情態(tài)動詞還有下列用途：  構成

4、疑問句附加語，如：   Mr Chen has not become a businessman, has he?   Jason's lectures are clear and easy-to-understand, aren't they?  構成簡短答語，如：   -Who can answer this question? -Sam can.   -Will you help us with the gardening? Yes, I will. /No, I won't.   -I have see

5、n that film before. -So have I.   -William isn't a hypocrite. -Neither is his wife.  構成省略句，如：   I can't understand him. Can you ?   The boss doesn't often come to the factory and when he does, it is generally on Sunday.  除了“do, be, have”之外，作為第三人稱現(xiàn)在時態(tài)（third person present tense）時，助動詞和情態(tài)動詞語尾不起變化，也就是不必有“-s”這形式。例如：  I can write English. He can write English, too. Tom will know soon, but he will never know.  All of you may go. Jack may also go if he wants to.  （注意“be”代表