英语单词until和not until有何区别

until 直到.为止He taught me English until the class was over.他教我英语,直到下课为止.not until 直到.才It was not until the class was over that he began to teach me English.直到下课之后他才开始教我英语...语法呢·····背后连什么动词语法都是一样的，都可以接两种成分：从句或者时间状语