動詞do在句中的作用可以概述為四句十二字："做"實義，助動詞，替前文，強語氣。

　　作用一：實義do

　　do作實義動詞時，有do, does, did, done, doing五種形式，還有及物、不及物之分。如：

　　1. vt. "做；研究；整理；完成"。如：

　　①The old man does an hour of sport every day.

　　②She did her homework at home last night.

　　③Mother was doing the cooking when I reached home.

　　④Have you done the exercises yet?

　　2. vi. "行動；工作；進展；足夠"。如：

　　①Kate does very well in her Chinese.

　　②How do you do?

　　③Well done!

　　④That will do.

　　作用二：助動do

　　do作助動詞時，只有do, does, did三種形式，無詞義，限用于含行為動詞的一般現(xiàn)在時和一般過去時兩種時態(tài)的否定句和疑問句中。如：

　　①They don't have any tickets for tonight's concert.

　　②Kate stayed at home last night, didn't she?

　　③How many books does the library have?