一、可以用作介词
⒈)指时间上早于，在……之前，如：
She has lived here since before the war.
她从战前就一直在这儿住。
⒉)指位置在前面，如：
We knelt down before Grandma's grave.
我们在奶奶的墓前跪下。
⒊)指顺序或排列在之前，如：
Your name comes before mine on the list.
名单上你的名字在我之前。
⒋)在某人面前，如：
She said it before the witness.
他是当着证人的面说的。
二、作为连词
其基本含义是“在……之前”，又可以根据不同语境灵活翻译成“才”、“还没来得及就……”、“趁……”、“就”等。具体用法如下：
⒈)与情态动词can/could连用
这时候从句虽为肯定形式，根据汉语表达习惯译成“还没来得及就”，如：
Before I could get in a word，he had measured me.
我还没来得及插话他就为我量好了尺寸。
Before she could move，she heard a loud noise，which grew to a terribl eroar.
她还没来得及迈步，就听见一声巨响，接着就是可怕的隆隆轰鸣。
⒉)用于肯定句中强调主句所表达的时间，距离长，或花费的精力大，译成“才”
We had sailed four days and four nights before we saw lands.
我们航行了四天四夜才看到陆地。
We waited a long time before the train arrived.
我们等了很长时间火车才到。
⒊)用于否定句中，强调主句所表达的时间，距离短，或花费的精力小，译成“不到……就”如：
We hadn't run a mile before he felt tired.
我们跑了还不到一英里他就累了。
⒋)主句含有hardly，scarcely等半否定副词时可以译为“刚……就”
这时候主句应用过去完成时态，从句用过去时，还可以用when替代before如：
We had scarcely reached the school before/when the bell rang.
我们刚到学校铃声就响了。
⒌)有时还有“宁愿”的意思
I'd shoot myself before I apologized to him.我宁死也不向他道歉。
⒍)用于It+be/take+时间段+before句型
在这一句型中又可以根据主从句的时态分成两种情况。
若主句是一般时将来时态，从句是一般现在时.若主句是肯定句意思是“要过多长时间才”;若主句是否定形式翻译成“用不了多久就”。
It will be two weeks before everything returns to normal.
两周之后一切才能恢复正常。
It will be many years before the situation improves.
这种状况或许要过许多年才能得以改善。
It won't be long before we meet again.用不了多久我们就会再见面的。
这时若主句是一般过去时从句也是一般过去时。若主句是肯定句翻译成“多长时间之后才”，若主句是否定形式翻译成“没过多久就”。如：
It was some time before I realized the truth.
过了很长一段时间我才了解到真相。
It wasn't long before she became a brave solider.
没过多久她就成了一名勇敢的战士。
After that it still took seven years before they got married.
他们又过了七年才结婚。
注意：当主句的谓语动词为延续性动词时，before与until有时可以互换。It was an hour before/until the police arrived.
巩固练习
⒈(2004天津)It was evening ________ we reached the little town of Winchester.
A.that B.until C.since D.before
2.(2004全国)Several weeks had gone by ________ realized the painting was missing.
A.as B.before C.since D.when
3.(2005广东)The America Civil War lasted four years ______ the North won in the end.
A.after B.before C.when D.then
4.(2005山东)It was some time _______ we realized the truth.
A.when B.until C.since D.before
5.(2006四川)-Why didn't you tell him about the meeting?
-He rushed out of the classroom _______ I could say a word.
A.before B.until C.when D.after
6.(2006福建)-How long do you think it will be __ china sends a manned spaceship to the moon?
-Perhaps two or three years.
A.when B.until C.that D.before
参考答案：D-B-B-D-A-D
