1. （am, is ,are 是be动词）如： I am a teacher．→I am not a teacher． This is a pen.→ This is not a pen.或This isn’t a pen. (is not =isn’t) You are a boy. →You are not a boy. (are not =aren’t)
2. （can是情态动词） He can help me．→He can not help me．或He can’t help me.(can not =can’t )
3.当主语是第一人称、第二人称和第三人称复数时用助动词do,变否定时，在do后面加not 如：I like English .I do not like English.或I don’t like English.
They go to school together. →They do not (don’t) go to school together.
4.当主语是第三人称单数时用does,变否定时，在does后面加not，如：The little girl wants to go there.→ The little girl does not (doesn't ) want to go there．
2．简单句中谓语动词为行为动词时，要根据时态选用do的相应形式，把肯定句变为否定句。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．祈使句变否定句时，一般在句首加Don't，但Let us或Let's开头的祈使句在 Let us或 Let's后加not也可。如：
Put them over there．→Don't put them over there．
Let us go home．→Let us not go home．
或Don’t let us go home.
4．主从复合句中，主句是I think，I believe等结构，变否定句时，形式上否定主句，实际上否定从句。如：
I don't think chickens can swim ．我认为鸡不会游泳。
5．“had better ＋动词原形”，变否定句时为“had better not ＋动词原形”。如：
You'd better go to school．→ You'd better not go to school．
6．动词不定式变否定式时，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．
7．使役动词和感官动词（make，let，hear，see，watch等）后接省略to的不定式，此种不定式变否定句时只需在省略to的动词原形前加not。如：
I saw her work．→ I saw her not work．
8．特殊形式的否定句，有以下几种：
（1）肯定句含有every-的合成词时，变否定句时改为no-。如：
Everything is ready．→ Nothing is ready．
（2）肯定句中含有always， usually和ever时，变否定句时改为never。如：
He is always late for school．→ He is never late for school．
（3）肯定句含有many，much时，变否定句时分别改为few，little。如：
Many students know him．→ Few students know him．
（4）肯定句中含有still时，变否定句时应改为no longer。如：
Tom is still in bed．→ Tom is no longer in bed．
（5）肯定句含有both， both．．．and，all时，变否定句时应改为never，neither．．．nor，none。如：
Both of us are students．→ Neither of us is a student．
（6）肯定句含有nearly， almost时，变否定句时应改为 hardly。如：
Lily nearly knows him ．→ Lily hardly knows him ．
（7）肯定句含有“形容词＋ enough”时，变为否定句时应改为“too ＋形容词的反义词”。如：
He is short enough to reachit． He is too tall to reach it．
（1）谓语动词是be，have（有）或谓语含有助动词、情态动词时，直接在这些词后加上否定词not。如：
She can swim． She can't swim．
（2）谓语动词是行为动词时，要在该动词前加上do ／does ／did not，该词恢复原形。如：
He gets up early． He doesn't get up early．
（3）既要否定谓语动词，又要变换句中的单词。如：
He can read and write． He can't read or write．
（4）用含否定意义的词或词组取代肯定句中的某些词或词组。如：
I know both English and Chi- nese． I know neither English nor Chinese．
类似的有：ever ／always never， somebody nobody，something nothing， everybody no one，almost hardly
2．祈使句的肯定式变否定式
（1）一般在动词前加上 don't。如：
Open the window ． Don't open the window．
（2）含有“Let's．．．”的祈使句，一般用“Let'snot．．．”的形式，美国人偶尔也用“Don'tlet's．．．”这一形式。加强语气时使用“Let'sdon't．．．”这一形式。如：
Let's go there． Let's not go there．
3．复合句的肯定式变否定式
一般将主句变为否定式。如：I saw her when I left ． I didn't see her when I left．
肯定句改为否定句的基本方法
把肯定的陈述句改为否定句的基本方法首先要掌握否定句构成的基本规则。
①当陈述句的谓语动词由 be构成时，改为否定句，把not加在be后面。
例1．They are doctors．
这个句子的谓语动词是由系动词构成的，改为否定句时把 not加在are的后面，即：They are not doctors．
例2．He is g oing to see his friend tomorrow．
本句的谓语由is going to see构成，改为否定句时把否定词not加在is后面，即：He is not going to see his friend tomorrow．
②当陈述句的谓语由情态动词can（may，must等）＋其他动词构成，或由助动词will， have，had等十其他动词构成时，改为否定句，用情态动词或助动词十not＋动词的形式表示。
例3．They will go to see their parents this afternoon．
这个句子谓语由助动词 will加动词g o构成，改为否定句时，把not放在will后面，即：They will not（won't） go to see their parents this afternoon．
例4．The train had already left when we got to the station．
这个句子谓语由助动词had加leave的过去分词left构成，改为否定句时要把not加在had后面，同时already改为yet，即： The train had not left yet when we got to the station．
例5．Linda can speak Chinese well．
本句的谓语由can＋speak构成，把它改为否定句时，在can后面加not，即：Linda can not speak Chinese well．
例6．We have already learned English for two years．
本句的谓语由have＋learned构成，把它改为否定句时，要在助动词have后面加not，把句中的already改为yet，即：We have not learned English for two years yet．
③当陈述句的谓语动词是have，表示有什么，改为否定句的方法是：（A）由have＋ not＋其他；（B）由have十no十其他；（C）由 don't（doesn't，didn't）＋have十其他，如果句中有some，要将some改为any。
例7．You have some books．
这个句子谓语动词have当“有”讲，在改为否定句时要把not放在have后，并把some改为any，即：You have not any books．这个句子也可以改写为在have后加no即：You have no books．这个句子还可以改写为：You don't have any books．
④当陈述句的谓语由have十其他词构成，这时have不当“有”讲，也不是“助动词”，改为否定句时，由助动词do（does，did）＋ not＋have构成否定结构。
例8．They often have breakfast at seven in the morning．
本句的谓语动词是have，而have＋ breakfast的意思是“吃早饭”，把它改为否定句，要由助动词do＋not＋have breakfast构成否定形式，即：They don't have breakfast at seven in the morning．
例9．He had a meeting yesterday afternoon．
本句谓语动词had＋meeting的意思是“开会”，是一般过去时，改为否定句时由did not＋have a meeting构成否定形式，即：He didn't have a meeting yesterday afternoon．
●以上两个例句说明改成否定句时，千万不要盲目把否定词加在have（has，had）后面。如果是由has或had ＋其他词构成的谓语改为否定句时，加上（does，did）not后要注意把has，had改为原形have。
⑤陈述句的谓语动词是行为动词，改为否定句时，要用助动词do（does，did）＋not＋行为动词构成否定形式。
例10．He studies English well．
本句的谓语由行为动词studies构成，把它改为否定句时要由助动词does＋not构成否定形式，即：He doesn't study English well．
例11．Her brother went to London in 1998．
本句的谓语由行为动词g o的过去式 went构成，改为否定句时，由助动词did＋ not构成否定形式，即：Her brother didn't go to London in 1998．
例12．Betty often does her homework after supper．
这个句子的谓语由行为动词does构成，要把它改为否定句，须用助动词does＋not并把其放在主语之后，同时把原句中的does改为原形即：Betty doesn't often do her homework after supper．
例13．He did it by himself．
本句的谓语由did构成，把它改为否定句要由助动词did ＋not构成否定式，并放在主语后面，同时要把原句中的did改为do，即： He didn't do it by himself．
●要注意加上does not或did not改为否定句以后，要把原句的动词改为原形动词，特别是行为动词do的第三人称单数does和过去时did，在主语后面加上doesn't或didn't以后，千万要注意把句中的does或did改为 do。
⑥祈使句的否定结构为：don't十原形动词。
例14．Look out of the window．
改为否定句时，要在句首加上don't，其它不变，即：Don't look out of the window．
⑦当陈述句中含有something这个词时，把句子改为否定句有两种方法：其一，在句中相应位置加not，再把something改成anything；其二，直接把som ething改为nothing即可。
例14．There is something wrong with the radio．
把这个句子改为否定句有两种方法：其一，先把not加在is后面，再把something改为anything即：There is not anything wrong with the radio．其二把som ething直接改为 nothing，即：There is nothing wrong with the radio．
例15．I have something important to tell you．
把这个句子变成否定句有两种方法：其中一种方法是先把not加在have后面，再把something变成anything，即：Ihave not anything important to tell you．第二种方法是直接把something改为nothing，即：Ihave nothing important to tell you．
⑧当陈述句是一个主从复合句，而主句的谓语动词是think或believe等时，把这种句子改为否定句，往往是否定think或believe
等而不否定后面从句中的谓语动词，尽管意思是否定从句的谓语动词。
例16．I think he will be back soon．
这个复合句中主句的谓语动词是think，所以在改为否定句时要在think前面加上 don't，即：I don't think he will be back soon．汉语意思：我认为他不会很快回来。但不能说：I think he won't be back soon．
⑨某些特殊句型改为否定句时，有不同的方法：
1）在陈述句中含有had better时，要把 not加在better后面，动词原形前面。
例17．You had better go with us．
把这个句子改为否定句，要把not加在 better之后，g o之前，即：You had better not go with us．千万不要改成：You had not better to go with us．或You had better don't go withus．因为，要否定的是后面的动词不定式短语。同时，had better后面要用动词原形（不带 to）。
2）当陈述句中含有both＋名词或者bothof＋名词作主语时，改为否定句时则用nei- ther代替both，并且要注意谓语动词数的变化。
例18．Both of them work in the school library．
句子含有both，改为否定句时用neither代替both，同时谓语动词work改为works，即：Neither of them works in the school library．
例19．Both answers are right．
把这个句子改为否定句，用neither代替 both，谓语动词are改为is，即：Neither answer is right．
3）句中含有both．．．and的肯定句改为否定句时用neither ．．．nor改写，同时neither．．．nor还可以把两个简单句的否定形式连成一个句子。
例20．Both Mary and Joan are students．
把这个句子改为否定句时，通常用Neither．．．nor代替Both．．．and，同时把are改为is，students改为a student即：Neither Mary nor Joan is a student．
●neither．．．nor连接两个主语时，谓语动词决定于nor后面的名词或代词的单复数形式。
例21．This book is both interesting and instructive．
把这个句子改为否定句，用neither．．．nor代替both．．．and，因为连接部分在句中作表语，所以谓语动词不变，
即：This book is neither interesting nor instructive．
例22．I don't see that film．He doesn't see it either．
这两个否定句可以用neither．．．nor连成一个句子，谓语动词改为肯定式see，人称和数由nor后面的he决定，即：Neither he nor I see that film ．，或者把I和he交换．即：Neither I nor he sees that film．这说明谓语的人称和数由nor后面的靠近谓语的人称和数决定。在把肯定句改为否定句时，注意把句中的 some，already，something等词改为any， yet，anything。
有一些表示否定意义的副词，如never， seldom ，hardly ，little ，few等也可以使句子成为否定句。例如：
He has few good friends here．
There is little water in the bottle．
I hardly believe it．
巩固练习：将下列句子改为否定句
1．We do morning exercises every day．
We _______ _______ morning exercises every day．
2．All of us can swim．
_______ _______ _______ can swim．
3．Both Joan and I are in Class One．
_______ Joan _______ I _______ in Class One．
4．There is som ething wrong with my bike．
There _______ _______ wrong with my bike．
5．You may stay here before I come back．
You _______ _______ here before I come back．
6．Read the text after me．
_______ _______ the text after me．
7．Li Lei needs som e help with his English．
Li Lei _______ _______ _______ help with his English．
8．He said he would g o to Beijing the next week．
He _______ _______ _______ _______ go to Beijing the next week．
9．The bike has already been m ended．
The bike _______ _______ mended _______ ．
10．Ithink it is going to rain tomorrow．
I _______ _______ _______ _______ going to rain tomorrow．
Key:
1．don't do 2．None of us 3．Neither；nor；am 4．is nothing 5．mustn't stay 6．Don't read 7．doesn't need any 8．didn't say he would 9．hasn't been；yet 10．don't think it is
