till / until在表達方式和意義上的特殊性：until是till的強調(diào)形式,但是它們表達的意義是相同的,都表示"直到某時".不過,當主句是否定句時,它引出的意思是"直到（某時）（某動作）才（發(fā)生）" ,這時候常會出現(xiàn)"not until …"的結構,如果將 "not until …"的結構放在句首,那么主句要寫成倒裝句.例如：
He didn't go to sleep until 12 last night .
他昨晚直到十二點鐘才睡覺.
They didn't realize their fault till we pointed it out to them .
直到我們向他們指出了他們的錯誤,他們才意識到.
Not until we pointed out their fault to them did they realize it .
直到我們向他們指出了他們的錯誤,他們才意識到.
但是,當主句是肯定句時,它引出的意思是"直到（某時某動作停止了）" .例如：
The students made much noise till the teacher came into the classroom .
直到老師走進教室學生們才停止了大聲喧嘩.
The young couple were very happy until they used up all their money .
那對年青夫婦直到花光了所有的錢才沮喪起來.
另外,until 可以放在句首而till則不行.我們可以說：Until they used up all their money,the young couple were very happy .我們卻不可以說：Till they used up all their money,the young couple were very happy .
此兩個連詞意義相同.肯定形式表示的意思是"做某事直至某時",動詞必須是延續(xù)性的.否定形式表達的意思是"直至某時才做某事".動詞為延續(xù)性或非延續(xù)性都可 以.正確使用這兩個連詞的關鍵之一就在于判斷句中的動詞該用肯定式還是否定式.
肯定句：
I slept until midnight.我一直睡到半夜時醒了.
Wait till I call you.等著我叫你.
（在肯定句中可用before代替 Let's get in the wheat before the sun sets.）
否定句：
She didn't arrive until 6 o'clock.
她直到6點才到.
Don't get off the bus until it has stopped.
公共汽車停穩(wěn)后再下車.
I didn't manage to do it until you had explained how.直到你教我后,我才會做.
1)Until可用于句首,而till通常不用于句首.
Until you told me,I had heard nothing of what happened.
直到你告訴我以前,出了什么事我一點也不知道.
2)Until when 疑問句中,until要放在句首.
---Until when are you staying?你呆到什么時候?
--- Until next Monday.呆到下周一.
注意：否定句可用另外兩種句式表示.
(1）Not until …在句首,主句用倒裝.
Not until the early years of the 19th century did man know what heat is.
直到19 世紀初,人類才知道熱能是什么.
Not until I began to work did I realize how much time I had wasted.
直到我開始工作,我才認識到了我已蹉跎了幾多歲月.
(2) It is not until… that…