一。将肯定句变为否定句时,一般情况下在句中助动词。系动词或情态动词后加not。但有时并非如此,而是要改变句中的某些词。现列举如下: 　　
(一)改变副词。
例如:　　1.He is always late for school.→　　　He is never late for school. 　　
2.The boy almost always goes to bed at 10 o'clock.→　　　The boy hardly ever goes to bed at 10 o'clock. 　　
3.He is still a worker.→　　　He is no longer a worker.　　
(二)改变连词。例如:　　Both Jim and Tom like reading.→　　Neither Jim nor Tom likes reading.　　
(三)改变不定代词。例如:　　All of the students are from the countryside.→　　None of the students are from the countryside. 　　
(四)改变限定词。例如:　　1.He spent much time playing every day.→　　　He spent little time playing every day.　　2.Many people know the news.→　　　Few people know the news.　　
二。肯定句变否定句时,既可以在句中助动词。系动词或情态动词后加not,也可以不加not,而只须改变句中的某些词。
例如:　1. He knows everything about your school.→　　He doesn't know anything about your school.　　He knows nothing about your school. 　　
2. I know both of them.→　　　 I don't know either of them.　　　I know neither of them. 　　3.Tom feels happy today.→　　　Tom doesn't feel happy today. 　　　Tom feels unhappy today. 　　4.The boy looks like his father.→　　　 The boy doesn't look like his father. 　　　The boy looks unlike his father.　　
三。变否定句时,某些形容词。不定代词。副词等也随之改变。
例如:　　1. I can see some mountains far away.→　　　 I can't see any mountains far away. 　　
2.He has already had breakfast.→　　　 He hasn't had breakfast yet. 　　
3.We can swim, too.→　　　We can't swim, either. 　　
4.Jim likes meat a little.→　　　Jim doesn't like meat at all.　　
四。当主句谓语动词是think, suppose, believe, guess和imagine等时,后面的宾语从句要表示否定意义时,
通常将not提到主句的位置上。例如:　　I think his proposal is valuable.→　　I don't think his proposal is valuable. 　　注:not和代词all, each, everyone, everybody及副词both, quite, altogether, always等连用时表示部分否定。例如:　　1.Not all the students prefer maths.并非所有的学生都喜欢数学。　　
2.It is not always sunny here.这里并不总是阳光普照。　　
3.The answer is not quite proper.这个答案不完全正确。

一。将肯定句变为否定句时,一般情况下在句中助动词。系动词或情态动词后加not。但有时并非如此,而是要改变句中的某些词。现列举如下: 　　
(一)改变副词。
例如:　　1.He is always late for school.→　　　He is never late for school. 　　
2.The boy almost always goes to bed at 10 o'clock.→　　　The boy hardly ever goes to bed at 10 o'clock. 　　
3.He is still a worker.→　　　He is no longer a worker.　　
(二)改变连词。例如:　　Both Jim and Tom like reading.→　　Neither Jim nor Tom likes reading.　　
(三)改变不定代词。例如:　　All of the students are from the countryside.→　　None of the students are from the countryside. 　　
(四)改变限定词。例如:　　1.He spent much time playing every day.→　　　He spent little time playing every day.　　2.Many people know the news.→　　　Few people know the news.　　
二。肯定句变否定句时,既可以在句中助动词。系动词或情态动词后加not,也可以不加not,而只须改变句中的某些词。
例如:　1. He knows everything about your school.→　　He doesn't know anything about your school.　　He knows nothing about your school. 　　
2. I know both of them.→　　　 I don't know either of them.　　　I know neither of them. 　　3.Tom feels happy today.→　　　Tom doesn't feel happy today. 　　　Tom feels unhappy today. 　　4.The boy looks like his father.→　　　 The boy doesn't look like his father. 　　　The boy looks unlike his father.　　
三。变否定句时,某些形容词。不定代词。副词等也随之改变。
例如:　　1. I can see some mountains far away.→　　　 I can't see any mountains far away. 　　
2.He has already had breakfast.→　　　 He hasn't had breakfast yet. 　　
3.We can swim, too.→　　　We can't swim, either. 　　
4.Jim likes meat a little.→　　　Jim doesn't like meat at all.　　
四。当主句谓语动词是think, suppose, believe, guess和imagine等时,后面的宾语从句要表示否定意义时,
通常将not提到主句的位置上。例如:　　I think his proposal is valuable.→　　I don't think his proposal is valuable. 　　注:not和代词all, each, everyone, everybody及副词both, quite, altogether, always等连用时表示部分否定。例如:　　1.Not all the students prefer maths.并非所有的学生都喜欢数学。　　
2.It is not always sunny here.这里并不总是阳光普照。　　
3.The answer is not quite proper.这个答案不完全正确。