一.I have a soccer ball改为否定句为I dont have a soccer ball，在have前面加dont,表示对have(有)的否定，就可以把句子改成否定句。
二.将肯定句改为否定句的方法。
1.谓语动词是be、have(作“有”讲)，或谓语动词有助动词、情态动词时，在它们的后面加not。若句中有some时，需将some改为any。例如：
I have some books on this subject.
I have not any books on this subject.
He can speak English.
He cannot speak English.
2.当谓语动词是行为动词时，而句中又没有情态动词或助动词时，需要在谓语动词之前加do not (或did not)来构成否定句。例如：
I know something about it.
I don’t know anything about it.
3.否定由think、believe、know等动词引出的宾语从句时，应将主句改为否定形式。例如：
She knows why the train is late.
She doesn’t know why the train is late.
4.祈使句的否定形式是在谓语动词前直接加do not。例如：
Read in bed.
Don’t read in bed.
5.如果肯定句是特殊句型，则要具体问题具体分析：
陈述句中含有had better时，变为否定句时，要把not加在better后。例如：
You had better go with me.
You had better not go with me.
