not… until直到…才
表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可以。
否定句：
She didn”t arrive until 6 o”clock.
她直到6点才到。
Don”t get off the bus until it has stopped.
公共汽车停稳后再下车。
I didn”t manage to do it until you had explained how. 直到你教我后，我才会做。
否定句可用另外两种句式表示。
(1)Not until …在句首，主句用倒装。
Not until the early years of the 19th century did man know what heat is.
直到19 世纪初，人类才知道热能是什么。
Not until I began to work did I realize how much time I had wasted.
直到我开始工作，我才认识到了我已蹉跎了几多岁月。
(2) It is not until… that…这是一个强调结构。
It is not until 8 o”clock that he didn·t do homework
他直到8点才写作业
unless 除非，如果不，等于“if not”本身就表示否定，引导
条件状语从句，主句为将来时，条件状语从句用
一般现在时表示将来。
一、作为
从属连词含义不同,引导从句性质不同
unless与until均为从属连词,unless表“除非”,强调条件,引导条件状语从句;until表“直到”,强调时间的延续,引导
时间状语从句。
1. I didn't know the news until my teacher told it to me.
2. I couldn't know the news unless my teacher told it to me.
3.—Was his father very strict with him when he was at school?
—Yes. He had never praised him until he became one of the top students in his grade.
析: 句1动词didn't know表明该句强调时间的延续,表“我不知道这消息”的状态一直延续到“老师告诉我”,因此应用until引导时间状语从句。句2动词couldn't know表明该句强调条件,表“我不可能知道这消息,除非老师告诉我”,因此应用unless引导条件状语从句。句3表明“他爸爸从来没有表扬他”的状态 一直延续到“他变成年级最好的学生之一”,因此也应用until引导时间状语从句。
二、作为从属连词引导的从句常用一般现在时表示将来
unless引导的条件状语从句和until引导的时间状语从句常用一般现在时表示将来。
例1:除非邀请你否则别进来。
误:Don't come in unless you will be invited to.
正:Don't come in unless you're invited to.
例2:除非他来,我们不可能去。
误:Unless he will come, we won't be able to go.
正:Unless he comes, we won't be able to go.
两者一般都不能互换