He needs help,doesn't he?此处的反意疑问句中为什么用doesn't?

问题描述:

He needs help,doesn't he?此处的反意疑问句中为什么用doesn't?
而You need't go yet,need you?中又为什么用need?

need在这里用作一般动词,所以和按照普通动词处理,用doesn't,在这里它不是情态动词,因为它后面没动词.help这是是名词.