till/until 1.在肯定句中，主句中谓语动词必须使用延续性动词，该动作延续到till/until 引出的时间停止。Eg: He stayed/sat up till/until his son came back. stayed/sat up 这个动作延续到his son came back这个时间停止。 在否定句中，主句中的谓语动词必须使用非延续性动词，该动作不到till/until 引出的时间不发生，直到till/until 引出的时间才发生。Eg: He didn’t go to bed till/until his son came back. go to bed 这个动作不到his son came back 不发生，直到his son came back才发生。 2. 倒装 否定副词位于句首引起句子的部分倒装。Eg: Not until his son came back did he go to bed. 3. 强调 在强调结构中，要求把not跟过去。Eg: He didn’t go to bed till/until his son came back. It was not until /till his son came back that he went to bed. 4. till 引导的分句不能位于句首。 (in order to/ so as to的区别：so as to 不能位于句首) Until his son came back he didn’t go to bed. 5. 主句是将来时，从句用一般时来替换将来时。Eg: He would stay/sit up until his son came back. 本文来源：https://www.wddqw.com/doc/7625fc9685c24028915f804d2b160b4e777f811d.html