巧辨before和until
在日常英語教學(xué)中，我們遇到學(xué)生問這樣的一些問題：1.He will spend six hours at his desk____he finishes his composition.A.before B.until C.after D.when
2.The bike hit the tree____I could get off.A.when B.before C.while D.until
3.I knocked at the door for more than five minutes____Mrs white answered it.A.until B.when C.after D.before
4.It was____yesterday____be____the secret.A.not until;that;knew B.until;when;knewC.not before;that;found D.before;that;didn't find
怎樣才能清楚地解釋其選擇的原因，這就涉及到until與before的區(qū)別問題。實(shí)際上，只要我們把握住兩者使用時(shí)本身的含義及主句動(dòng)詞是終止性的，還是延續(xù)性的，肯定式，還是否定式兩大點(diǎn)，就能容易地解決這類問題。
現(xiàn)詳細(xì)闡明如下：一、在下列情況下，兩者可互換用，但含義略有不同。before表示“在……之前”的意思，強(qiáng) 調(diào)時(shí)間先后關(guān)系;而until表示“直到……才”的意思，主句是肯定句則表示主句動(dòng)作的終止時(shí)間;主句是否定句則強(qiáng)調(diào)主句動(dòng)作的起始時(shí)間。
1.主句為否定式終止性謂語動(dòng)詞。常見的動(dòng)詞open,start,leave,arrive,finish, stop等。
(1)The noise of the street didn't stop until/before it was midnight.
(2)The children won't come back until/before it is dark.
(3)I didn't leave the lovely boy until/before his mother came home.
2.主句為肯定式、延續(xù)性謂語詞，這類動(dòng)詞用stand,stay,talk,be,wait等。
(1)He lived with his parents until/before he graduated from school.
(2)I will wait until/before he comes to my help.
(3)I shall stay heer until/before you come back.
二、在下列情況下，用before不用until。1.主句這肯定式、終止性謂語動(dòng)詞，只用before。
(1)He fell asleep before I could take off his clothes.
(2)We arrived there before it atarted to rain.
(3)The holiday came to the end befor I knew it.
(4)He almost knocked me down before he saw me.
2.主句謂語動(dòng)詞強(qiáng)調(diào)動(dòng)詞的遲緩性，只用before，常伴有時(shí)間段狀語或時(shí)間段暗示。
(1)It was quite some time before he found the elephant at all.
(2)We had walked a long way before we found some water.
(3)We had sailed for two days before we saw the land.
(4)The fire lasted about four hours before the firefighters could countrol it.
(5)It was midnight before my brother came home.
3.如果強(qiáng)調(diào)從句謂語動(dòng)作未發(fā)生，就發(fā)生主句謂語動(dòng)作，只用before。常譯為“未及”，“不”或“不等……就”。
(1)We can leave early in the morning before it gets too hot.
(2)I must write it down before I forget it.
(3)We do want to buy something now before prices go up.
4.表“與其說……倒不如”，“與其……毋寧……”只用before。
(1)I would give up my job before I'd agree to be dismissed.
(2)He will die of hunger before he will steal.
5.在某些特定句型中用before。
(1)It was not long before the whole country rose up.
(2)It will probably not be long before they understand each other.
三、下列情況一般區(qū)別用until1.主句是持續(xù)性謂語動(dòng)詞時(shí)，肯定、否定都可以，但意義完全不同�？隙ū韯�(dòng)作終止，而否定表動(dòng)作開始。
(1)We discussed the problem until/before he came back.我們一直討論到他回來。
(2)We didn't discuss the problem until he came back.我們一直等到他回來后才討論問題。
2.not…until句型盡管在某些情況下可與before互換用，但在強(qiáng)調(diào)句中一般仍用until。
(1)It was not until he told me that I knew it.
(2)It was not until he finished his homework that he went home.
綜上所述，前面的4條選擇題中，第1、3題強(qiáng)調(diào)動(dòng)作發(fā)生的遲緩性應(yīng)選before。第2題表動(dòng)作未及發(fā)生就發(fā)生主句動(dòng)作也應(yīng)選before。第4題為強(qiáng)調(diào)句應(yīng)選A項(xiàng)。
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