肯定句变否定句的基本方法一、动词be 的否定式动词be根据不同的人称和时态可以有am, is, are, was, were等不同形式，可用作连系动词(表示“是”、“在”等)和助动词(用于构成进行时态和被动语态等)，但不管何种情况，构成否定式时，一律在其后加notI’m old, but you’re young. 我老了，但你还年轻。
→I’m not old, but you’re not young. 我还不老，但你不年轻了。
He was reading and I was writing. 他在读，我在写。
→He was not reading and I was not writing. 他没有在读，我没有在写。
二、动词have 的否定式动词have根据不同的人称和时态可以有have, has, had等形式，可以用作实意动词和助动词，分以下情况讨论1. 用作实意动词表示状态，如表示拥有、患病或用于have to表示“必须”等，在构成否定式时可以直接在其后加not，也可根据情况在其前使用don’t, doesn’t, didn’tHe has a car. 他有辆小汽车。
→He hasn’t a car. / He doesn’t have a car. 他没有小汽车。
He had some dictionaries. 他有一些词典。
→He hadn’t any dictionaries. / He didn’t have any dictionaries. 他没有词典。
You have to go with him. 你必须同他一起去。
→You haven’t to go with him. / You don’t have to go w ith him. 你不必同他一起去。
【注】have to构成否定式时以在其前加don’t等较为常见。
2. 用作实意动词表示动作，如表示“吃(=eat)”、“喝(=drink)”、“拿(=take)”、“收到(=receive)”、“度过(=spend)”等，构成否定式时不能直接在其后加not，而应根据情况在其前使用don’t, doesn’t, didn’tHe had some cake for breakfast. 他早餐吃了些蛋糕。
→He didn’t have any cake for br eakfast. 他早餐没有吃蛋糕。
(不能用had not)We had a good holiday. 我们的假期过得很愉快。
→We didn’t have a good holiday. 我们的假期过得不愉快。
(不能用had not)3. 用作助动词构成完成时态，其否定式只能在其后加notI have read the book. 我读这本书。
→I have not read the book. 我还没读这本书。
He had left when I arrived. 我到达时他已离开了。
→He hadn’t left when I arrived. 我到达时他还没有离开。
三、情态动词的否定式情态动词的否定式一般在其后加not构成I can finish the work in an hour. 我能在1小时内完成这工作。
→I can’t finish the work in an hour. 我不能在1小时内完成这工作。
You must go with us. 你必须同我们一起去。
→You mustn’t go with us. 你不能同我们一起去。
We should help them. 我们应该帮助他们。
→We shouldn’t help them. 我们不必帮助他们。
四、实意动词的否定式一般实意动词的否定式，通常应根据不同时态和人称在实意动词之前加don’t, doesn’t, didn’t等He works in a bank. 他在一家银行工作。
→He doesn’t work in a bank. 他不是在银行工作。
We often hear from her. 我们经常收到她的来信。
→We don’t often hear from her.我们不经常收到她的来信。
I met her at the station. 我在车站见到了她。
→I didn’t meet her at the station. 我在车站没见到她。
●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。
五、祈使句的否定结构为：don't十原形动词。
改为否定句时，要在句首加上don't，其它不变，即：Look out of the window．→Don't look out of the window．六、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something改为nothing即可。
例．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something直接改为nothing，即：There is nothing wrong with the radio．例.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：I have not anything important to tell you．第二种方法是直接把something 改为nothing，即：I have nothing important to tell you．七、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．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。
八、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．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 with us．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both of＋名词作主语时，改为否定句时则用neither代替both，并且要注意谓语动词数的变化。
例．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．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．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．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．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．_______ Joan _______ I _______ in Class One．4．There is something 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 some 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．I think 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。