untill和till的用法

till /和until在表达方式和意义上的特殊性：until是till的强调形式，但是它们表达的意义是相同的，都表示"直到某时"。不过，当主句是否定句时，它引出的意思是"直到（某时）（某动作）才（发生）" ，这时候常会出现"not until …"的结构，如果将 "not until …"的结构放在句首，那么主句要写成倒装句。例如：

Hedidn'tgo to sleep until 12 last night .
他昨晚直到十二点钟才睡觉。
Theydidn'trealize their fault till we pointed it out to them .
直到我们向他们指出了他们的错误，他们才意识到。
Not until we pointed out their fault to them did they realize it .
直到我们向他们指出了他们的错误，他们才意识到。

但是，当主句是肯定句时，它引出的意思是"直到（某时某动作停止了）"。例如：
The students made much noise till the teacher came into the classroom .
直到老师走进教室学生们才停止了大声喧哗。
The young couple were very happy until they used up all their money .
那对年青夫妇直到花光了所有的钱才沮丧起来。

另外，until 可以放在句首而till则不行。我们可以说：Until they used up all their money,the young couple were very happy .我们却不可以说：Till they used up all their money,the young couple were very happy .