动词表示动作形态,但英语里有些动词并不表示动作形态,而是协助主动词表示时态(tenses)或语态(voices)。这些动词如 do, is, have等,叫助动词(auxiliary verbs)。另外有些动词如can, will, may, must等,则可协助动词表示语气或情态,叫情态动词(modal verbs)。
助动词和情态动词都是特殊动词,非常有用。没有了它们,疑问句不能成立,否定句也难形成。没有了have, has, had完成时态(perfect tenses)无法存在;没有了be, is, are, am, been, was, were, being,何来被动语态(the passive voice)?请看下列例子,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 wont.
● -John lived here before.
-John did not live here before.
● -Betty has completed her work 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.
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