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1、unless 的基本用法连词 unless 意为“除非如果不”,“除了”,多引导一个否定意义的真实条件句, 有时也可引导非真实条件旬。unless 引导条件句时,主要用于下列情况。(1)主句为肯定句。如:Unless I visit every bookstore in townI shall not know whether I can get what l want如果我不到 城里每一家书店去看看,我就不知道是否能买到我想要的书。You will miss the bus unless you hurry up你要不快点就会错过班车。Youll fail in chemistry agai
2、n unless you work harder如果你不再加把劲,你化学考试还会不及 格。(2)主句为否定句。如:Unless you oil the motor regularlyit wont run smoothly要不是你经常给发动机上油。它就不 会转得那么顺畅。I wouldnt be saying this unless I were sure of the facts要是我对这些事情没有把握,我就不说这 话了。You will never get anywhere unless you have set your goal如果你不设定目标,你哪儿也去不了。二、应注意的一些问题1u
3、nless 不能与 if“not 换用的情况unless 在意义上相当于 if.not,因此在有些场合中 unless 与 if.not 可互换使用。如:Unless I am mistakenIve seen that man before=lf I am not mistaken。Ive seen that man before如果我没搞错,我以前见过那个人。Unless the strike has been called off,there will be no trains tomorrow=lf the strike has not been called off。there wi
4、ll be no trains tomorrow除非罢工结束了,明天才会有火车。但在有些情况下,二者不可互换使用。如:(1)当 unless 引导非真实条件句时,一般不可改用 if.not。如:They couldnt afford to live in such an expensive apartment unless they were rich除非他们很富 有,否则就住不起这么昂贵的公寓。They couldnt have arrived at the site instantly unless the police had had a helicopter除非警方有 直升机,不然他们
5、就不会即刻赶到事发地点。以上两例中,unless 从句均表示与事实相反的情况。如果把 unless 换成 if.not(if they were not rick,if the police had not had a helicopter)就与原句意义完全相反了。(2)if.not 引导的条件分句可以重叠使用,unless 则不可,因为 unless 表示唯一条件,不能用 and 连接两个 unless 引导的从句。如:She wont lose weight if she does not keep a diet and if she does not take exercise ever
6、y day=She wont lose weight unless she keeps a diet and takes exercise every day除非她坚持节食、每天锻炼, 否则是不能减肥的。(3)unless 引导的条件句可用否定结构,而 if.not 引导的条件句不可再加以否定,因为两个 not 不能重叠使用,因此在 unless 引导的否定条件旬中,不能用 if.not 替代 unless。如: Dont ask me to explain unless you really dont understand除非你真不懂,不然别让我解释。The directors have a
7、 meeting every Fridayunless there is nothing to discuss董事会每周五开会, 无事讨论除外。You will get a good grade in the course unless you dont do your homework如果你(不是不)做作 业的话,你就会有好的学业成绩。(4)当 if 引导名词性从句时,unless 不可以代替 if.not,因为 if=whether(“是否”)。如:It is unimportant if he will not attend the graduation ceremony他是否参加毕业典
8、礼无关紧要。I doubts if he has not made a contribution to the environment我怀疑他是不是没有为环保做过贡 献。(5)当 unless 作介词(“除以外”,“除非”)时,if.not 不能与其互换使用。如:Nothing will come out of itunless(=except)disaster这件事除了引起灾祸之外,不会有什么结果。Nothingunless a miracle,can save him除非出现奇迹,否则他无法得救。2unless 从句中成分的省略unless 从句的主语与主句的主语相同时,unless 从句
9、中的主语和谓语(或一部分)有时可省略。如:Unless(he is)in uniform。he doesnt look like a policeman如果不穿上制服,他看起来就不像警 察。Unless(I am)compelled t0 stay in by bad weather,I go for a walk every day若非天气不好被迫呆 在家里,我每天都出去散步。Dont leave the building unless(you are)instructed to do so没有得到通知,不要离开大楼。The virus is capable of destroying an
10、 information stored in a computer unless(it is)detected and eradicated病毒如不查出并清楚掉,会把存储在计算机里的资料全部毁掉。3unless 从句的时态主句是一般将来时态、祈使句或谓语中含有情态动词或主句是一般现在时,unless 引导的真实 条件句用一般现在时;如果强调从句动作发生在主句动作之前,从旬可用现在完成时。Dont touch the instruments unless the teacher allows you没有老师的允许,不要乱动仪器。Unless you know a word,you may con
11、sult a dictionary如果你不认识哪个词,你可以查词典。但主句是过去将来时或过去时,unless 引导的真实条件句常用一般过去时。如:The disease prevented him from remembering things unless he was reminded by another这种病使 他记不住事,只能靠别人提醒。4“祈使句(肯定式)+orotherwise+陈述句”与“unless 条件句+主句”间的转换“祈使旬(肯定式)+or(else)otherwise+陈述句”与“unless 条件句+主句”间有时可以相互转换。 如:Put on your rainc
12、oat or youll get soaked=Unless you put On your raincoat,youll get soakedIf you dont put on your raincoat,youll get soaked把雨衣穿上,否则你就 会全身湿透的。Store the meat in the fridge,otherwise it will go the fridge,otherwise it will go offIf you dont store the meat in the fridge,it will go off把肉放在冰箱里,不然就会坏掉。5在 unl
13、es 引导的肯定形式的条件句中。通常用肯定词(some,already, still,too,as well 等);在 if.not 引导的条件句中通常用非肯定词(anyyetevereitherat all 等)You ll never really know what happiness is unless you have something to compare it to只有通过对 比,才能了解幸福的含义。1 will inform her if you havent spoken to her yet如果你还没跟她说,我通知她。不过在 ifnot 引导的非真实条件句中,仍能用肯定词
14、,因为这种条件句形式上是否定,意义上 却是肯定。如:If he hadnt already prepared his lesson,he wouldnt be allowed to go要是他没有做完功课, 是不会允许出去的。(实际已做完功课)6unless 可用来引导出补充前言的句子unless 引导出补充前言的句子,即对刚说过的话又突然想到要补充的内容。如:He hasnt got any hobbies unless you call writing a hobby他没有任何嗜好除非把写作也算 作嗜好。Lets play chess unless you really have something urgent to do下盘棋吧除非你真有急事要 办。