在不定式標志to前加上not.例如：

　　Tell him not to shut the window.讓他別關窗。

　　She pretended not to see me when I passed by. 我走過的時候，她假裝沒看見。

　　典型例題

　　1）Mrs. Smith warned her daughter ___ after drinking.

　　A. never to drive　 B. to never driver　 C. never driving　 D. never drive

　　答案：A.warn sb to do sth. 的否定形式為warn sb not to do sth. 此處用的是否定詞never.

　　2） The boy wanted to ride his bicycle in the street，but his mother told him ____.

　　A. not to　　B. not to do　　C. not do it　 D. do not to

　　答案：A.not to 為not to do it 的省略形式。可以只用to這個詞，而不必重復整個不定式詞組。及物動詞do后應有賓語，因此也B，D不對。