和助動詞後加not。如： I am a teacher．→I am not a teacher．He can help me．→He can"t help me．2．簡單句中謂語動詞為行為動詞時，要根據時態選用do的相應形式，把肯定句變為否定句。如：The little girl wants to go there．→The little girl doesn"t want to go there．He did his work yesterday．→ He didn"t do his work yesterday．3．祈使句變否定句時，一般在句首加Don"t，但Let us或Let"s開頭的祈使句在 Let us或 Let"s後加not即可。如：Put them over there．→Don"t put them over there．Let us go home．→Let us not go home．4．主從複合句中，主句是I think，I believe等結構，變否定句時，形式上否定主句，實際上否定從句。如：I don"t think chickens can swim ．我認為雞不會游泳。5．“had better ＋動詞原形”，變否定句時為“had better not ＋動詞原形”。如：You"d better go to school．→ You"d better not go to school．6．動詞不定式變否定式時，常在不定式to前加not。如：The teacher tells me to do it．→ The teacher tells me not to do it．
和助動詞後加not。如： I am a teacher．→I am not a teacher．He can help me．→He can"t help me．2．簡單句中謂語動詞為行為動詞時，要根據時態選用do的相應形式，把肯定句變為否定句。如：The little girl wants to go there．→The little girl doesn"t want to go there．He did his work yesterday．→ He didn"t do his work yesterday．3．祈使句變否定句時，一般在句首加Don"t，但Let us或Let"s開頭的祈使句在 Let us或 Let"s後加not即可。如：Put them over there．→Don"t put them over there．Let us go home．→Let us not go home．4．主從複合句中，主句是I think，I believe等結構，變否定句時，形式上否定主句，實際上否定從句。如：I don"t think chickens can swim ．我認為雞不會游泳。5．“had better ＋動詞原形”，變否定句時為“had better not ＋動詞原形”。如：You"d better go to school．→ You"d better not go to school．6．動詞不定式變否定式時，常在不定式to前加not。如：The teacher tells me to do it．→ The teacher tells me not to do it．