till / until在表達(dá)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(dá)的意義是相同的,都表示"直到某時".不過,當(dāng)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(jié)構(gòu),如果將 "not until …"的結(jié)構(gòu)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(dāng)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(jìn)教室學(xué)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(dá)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(guān)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(jì)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(rèn)識到了我已蹉跎了幾多歲月.
(2) It is not until… that…