Question

否定句到底什么时候用doesn't什么时候用isn't?谢谢！

Answer 1

doesn't 和 isn't 是 does 和 is 的否定词（或反义词），因此 doesn't / isn't 的用法和 does / is
一样， 也就是说，
He/she/it doesn't 表达动作，即 他/她/它 "做" 或 “操作” 某某事，通常接动词
而
He/she/it isn't 表达状态， 即 他/她/它 “是” 某某 东西 或 “处于” 某某状态 ，通常接名词，形容词或动词进行时态（现在分词）
例句：
He doesn't go sailing anymore, ever since his boating accident.
He isn't a carefree person that he used to be, ever since the mishap.
He isn't carefree like he used to be, ever since the mishap.
With the memory of the accident still fresh in mind, he isn't going sailing much.

Answer 2

doesn't是否定行为动词的，后面跟动词原形。例如：doesn't go/do/sing/work。
isn't 是跟名词、形容词、动词的ing、动词的ed，副词、介词短语等。例如：He isn't at home/a student/in the room/in/good/interesting/excited.
很高兴为你解答！
老师祝你学习进步！
请及时采纳哦！多谢你的问题！^_^

Answer 3

当前面是动词时用doesn't，是名词时用isn't。动词用助动词修饰，名词用be动词。