If引导的条件句具有使用频率高,形式多样化、含义变化多端等特点。在高中阶段我们有必要正确理解、把握和使用,从而对主从句之间的逻辑关系有正确的认识。
一、If引导的非真实条件从句
If引导的非真实条件从句,已经引起大家的高度重视,尽管高考考试说明中对If引导的非真实条件从句不是高考项目,但高考中还是出现了,并且对If引导的非真实从句,也与各种时态、情态动词及用法、虚拟、语气、倒装等语法功能相联系,因此,越来越得到高考出题人的青睐。下面是大家熟悉的三种非真实条件从句中虚拟语气构成情况:
⑴表示现在的假设,其构成如下:
条件从句 主句
动词的过去式(be的过去式多用were) Would[should,could,might]+原形动词
如:
①If I were you, I should do that.
如果我是你,我会做那事的。
②We would go with you if we had time.
我们如果有时间,会和你一块去的。
③If he were here,it could be done.
如果他在这儿,这事就可以办。
⑵表示过去的假设,其构成如下:
条件从句 主句
had+过去分词 would[should,could,might]+have+过去分词
如:
①If I had seen you yesterday, I would have asked you about it .
如果我昨天看到你,我就会问你这件事。
②If he had been there last night, it would not have happened .
如果他昨晚在那里,这事就不会发生。
③If you had come a little earlier, you could have met him .
如果你早点来,你就能碰到他。
⑶表示将来的假设,其构成如下:
条件从句 主句
动词过去式/should+原形动词/were to+原形动词 would[should, could,might]+原形动词
如:
①If anyone set me free, I would make him very rich.
如果有人放我出来,我会让他十分富有。
②If it should rain, the crops would be saved.
如果有雨,庄稼就可能有救。
③If it were to snow tomorrow, they would not go for an outing.
如果明天下雪,他们就不外出游玩。
④I think we could do it well if we planned it properly and could borrow the tools.
如果我们计划得好并能借到工具,我想我们能干好这事。
注:在if从句中若含有had/should/were,可把if省去,然后句子倒装。如:①Were I you,I should do that ②Had I seen you ,I would have told you about it. ③should it rain , the crops would be saved.
二、开放性If-条件句
开放性If-条件句可分为3种:(一)直接条件句;(二)间接条件句;(三)其它用法。下面分别加以说明。
(一)直接条件句
直接条件句是指主从句关系密切,从句是主句动作不可少的条件。又可分为以下几种情况。1、表“现在条件”
在该类条件句中,谓语动词的动作与现在时间有关,说明主句动作发生以“现在条件”为前提。这种条件句的主句可用be going to结构,因为无论be going to结构表现在打算做还是有迹象表明了将发生,均与现在时间有关。
如:
①Were going to be surrounded by the enemy if we walk on like this.(照我们这个样子走下去,我们会被敌人包围的。)
②He is working too hard , If he does not .(他工作太努力了。若不放松一下,他会跨掉的。)
2、表示“将来条件”
在此类从句中,谓语动词单纯表“将来”,与现在时间没关系,因而主句不能用be going to 结构。
如:
①If you swim this afternoon, you will be too tired to go shopping with me.(如果下午你去游泳,你会累得无法和我去购物。)
②If you study hard, you will succeed sooner or later (如果学习努力的话,你迟早会成功的。)
以上两个例句中从句都以将来的事实为条件,(但动词用一般时态代将来),说明只有当将来条件成为事实,主句动作才能发生,(主句用will)通过1)与2)区别,我们也能区分be going to与will的细微差别:be going to 与现在时间有关的打算或迹象表明,will表将来。
3、表“动作的完成”
在这种条件名中,谓语动词的动作已完成,常用现在完成体,说明主句动作的发生是以从句动作的完成为条件,前提。
如:If you have finished your homework , you can go out to play now.
4、表示“意愿”
当条件名表意愿时,其谓语部分要用will/would结构(will/would不再是助动词表将来,而是情态动词)
如:①If you would make an enemy , lend her money and ask it of her again(如果你想树敌的话,那就借给他钱再讨回来)
②John will come here tomorrow,if he will come.(如果约翰原来的话,他明天就可到达)
5、表“预测”(will仍为情态动词)
如:If he won’t arrive before nine, there is no ticket for him .(如果9点前他来不到的话,就没票卖给他了。)
6、表“习惯性行为”和“自然规律”
如:Salt melts if it is put into water(把盐放入水中会化的)
此时if相当于when或whenever
7、表“机会”或“不确定性”
条件句表这个意思时,一般要用should结构。
如:If
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