until和before的区别

下列情况下，两者可互换使用，但含义略有不同。
一。Before表示“在… 之前”，而until表示“直到…才…”，主句肯定表示主句动作的终止时间，主句否定强调动作的起始时间。
1,主句为否定时，谓语动词为终止性动词。常见的动词有open, start, leave, go, arrive, finish, begin, stop, etc.
For example:
1), The noise of the street didn’t stop before/until it was midnight.
2), The children won’t come back until/before it is dark.
3), I didn’t leave the lonely boy before/until his mother came home.
2,主句为肯定式，谓语为延续性动词。这类动词有：stand, live, stay, talk, be, wait, etc.
For example:
1). He lived with his parents until/before he graduated from school.
2). I will wait before/until he comes to my help.
3). I shall stay here until/before you come back.
二。列情况下宜用before不用until.
1。主句为肯定式，谓语为终止性动词时只用before.
For example:
1). He fell asleep before I could take off his clothes.
2). We arrived there before it started to rain.
3). The holiday came to an end before I knew it.
4). He almost knocked me down before he saw me.
2。主句谓语动词强调动作的迟缓性，只用before,这时常伴有时间段状语或时间段暗示。
For example:
It was quite a long time before he found the elephant.过了很长时间，他才找到大象。
We had walked a long way before we found some water.走了很长的路我们才找到水。
We had sailed for two days before we saw the land.航行了两天我们才发现陆地。
It was midnight before my brother came home.我哥哥直到半夜才回来。
3。如果强调从句谓语动作未发生就发生主句谓语动作，只用before,这时常译为“未及（不等）……就……”
For example:
1）We can leave early in the morning before it gets too hot.趁天还不太热，我们上午早点离开。
2）I must write it down before I forget it.趁我还未忘，我必须把它记下来。
4。表示“与其说……倒不如……”,“与其……毋宁……”的意思时只用before.
For example:
I would give up my job before I agree to be dismissed.我与其被解雇还不如先辞职。
He will die of hunger before he steals.他宁愿饿死也不愿意去偷。
5．在某些特定句型中用before。
It was (not) long before…（不久）过了很长时间才…
It will (not) be long before…（不到）要过很长时间才会…
For example:
.It will probably not be long before they understand each other.
他们大概过不久就会互相了解。
It was not long before the whole country rose up.
不久全国人民奋起反抗。
三.下列情况一般使用until
1。主句是持续性谓语动词时，肯定,否定都可以，但意义完全不同，肯定表示动作终止，而否定表示动作开始。
For example:
1). We discussed the problem until/before he came back.
我们一直讨论到他回来。
2). We didn’t discuss the problem until he came back.
我们一直等到他回来才讨论问题。
2．Not…until…句型尽管在某些情况下可与before互换使用，但在强调句中一般仍用until;
1). It was not until he told me that I knew it.直到他告诉我我才知道这件事。
2）.It was not until he finished his homework that he went home.直到完成作业他才回家。
3）放于句首时用until.
For example:
Antil he finished his homework ，he didn’t go home. 直到完成作业他才回家。
应注意：在使用not until时，若not until放于句首，句子应部分倒装。 For example:
Not until he finished his homework，did he go home. 直到完成作业他才回家。