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…
