肯定句变否定句
1.I am a student. → I am not a student. 2.You are sad. → You are not sad. 3. She is a good girl. → She is not a good girl. 4.Yesterday was Monday. → Yesterday was not Monday. 5.They were busy yesterday. → They were not busy yesterday
1.如果句中有be动词（ is, am , are, was, were),就在be动词后面直接加not。
be 动词和not的缩写形式：
is not = isn't are not = aren't was not = wasn't were not = weren't
注意：am not 不能缩写。
1. He is a boy. He is not a boy. 2. I am your friend. I am not your friend.
3. My sister is a beautiful girl. My sister is not a beautiful girl.
4.There are some books on the bookshelf. There are not any books on the bookshelf.
5. I was at home yesterday. I was not at home yesterday. 6. They were in Beijing ten years ago. They were not in Beijing ten years ago.
注意：句中有some,一般要改为any.
1.I can swim. → I can not swim.
2.You will go to the park. → You will not go to the park. 3. Peter need go home now. Peter need not go home now 4. You should open your book. You should not open your book. 5. He must finish his homework. He must not finish his homework.
2.如果句中有（can ,may, must, should ,need, will等），就在这些单词后面直接加not。
can not = can't must not = mustn't should not = shouldn't need not = needn't will not = won't
1. Lucy will be back in a week. Lucy won't be back in a week. 2. You can use the dictionary. You can't use the dictionary. 3. Peter need go home now. Peter needn't go home now . 4. You should say “Sorry”.
You shouldn't say “Sorry”. 5. He must stay at home . He mustn't stay at home .
3.如果句中没有be动词，也没有情态动词，就要借助（don’t, doesn’t, didn’t）来帮忙。
①当句中的动词是原形时，在动词前直接加don’t。
I like English. → I don't like English. You have dinner. → You don't have dinner.
肯定祈使句变否定祈使句，也是在动词前加直接don't.
3. Have some bread, Tom. Don't have any bread ,Tom. 4. Please open your books. Please don't open your books.
②当句中的动词是第三人称单数时，在动词前加doesn’t ，动词还原原形。
She likes singing. → She doesn’t like singing. She does her homework. → She doesn’t do her homework.
③当句中的动词是过去式时,在动词前加didn’t，动词还原原形。
We had a great time last year.→ We didn't have a great time last year. I went to school yesterday. → I didn't go to school yesterday.
肯定句变否定句 练一练
1. I am your friend. _____________________________