A. 帮助构成时态的:The boy is crying. (is 用来帮助构成现在进行时,和crying一起作谓语,是助动词。)He has arrived. (has用来帮助构成现在完成时,和arrived一起作谓语,是助动词。)I have been painting all day. (have been用来帮助构成现在完成进行时,和painting一起作谓语,都是助动词。)
B. 帮助构成否定句和疑问句的:Does he like English? (does帮助构成一般疑问句,没有具体意义,是助动词。)He doesn’t have lunch at home. (does只是帮助构成否定句,没有具体意义,是助动词。)
C. 帮助构成被动语态的Trees are planted in spring. (are帮助构成被动语态,没有具体意义,是助动词。)The house has been pulled down. (has been帮助构成时态和语态,是助动词。)
D. 帮助构成虚拟语气If he had come yesterday, I wouldn’t have made such a mistake.(had, have帮助构成虚拟语气,是助动词,属于谓语的一部分。)
E. 帮助构成倒装句的So much did he love his mother that he bought her many presents on her birthday.(他如此爱他的母亲以至于他母亲生日那一天,他给她买了许多礼物。did只是帮助构成倒装句,没有具体意义,是助动词。)
F. 帮助构成强调意义的He did come yesterday. (他昨天确实来过。did起强调作用,没有具体意义,是助动词。)
因此可以看出,常见的助动词为do, be, have,它们为基本助动词。一个词既可以作实义动词也可以作助动词,具体是哪一种,主要看它们在句中的功能。
① He did his homework at seven o’clock. (did单独作谓语,意为“做”,是实义动词。)Did he do his homework yesterday? (did是助动词,帮助构成一般疑问句,do是实义动词,意为“做”,是实义动词。)
② He has had breakfast. (has是助动词,帮助构成现在完成时,had是实义动词,意为“吃”。has had一起构成了句子的谓语。)