虚拟条件句的三种基本类型一、与现在事实相反若与现在事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”。如：If you took a taxi，you’d get there quicker. 如果你坐出租车去，你可以快一点到那里。(但你不坐)If I knew her number I could ring her up. 要是我知道她的电话号码，我就可以给她打电话了。(可惜我不知道)二、与过去事实相反若与过去事实相反，条件从句的谓语用过去完成时(had+过去分词)，主句谓语用“should (would, could, might)+have+过去分词”。如：If I’d left sooner，I’d have been on time. 要是我早点动身，我就准时到了。(但我动身太迟了)If we had found him earlier we could have saved his life. 要是我们当时早点找到他的话，我们就可以救活他。(可惜我们找到他太晚了)三、与将来事实相反若与将来事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”。如：If he went，would you go too? 如果他去，你也去吗?(大概他不会去)If I asked him，I’m sure he’d help us. 如果我向他提出要求，肯定他会帮助我们。(不过我不打算这样做)【注】① 主句谓语中的should主要用于第一人称后。would, might, could的大致区别是。如：would表示结果，might表示可能性，could表示能力、允许或可能性。比较：If you tried again you would succeed. 要是你再试一试，你就会成功的。(would表结果)If you tried again you might succeed. 要是你再试一试，你可能会成功的。(might表可能)If you tried again you could succeed. 要是你再试一试，你就能成功了。(could表能力)② 条件从句的谓语动词为be时，不管其主语为单数还是复数通常都用were，但在口语或非正式文体中的单数第一人称和第三人称后，也可用was，不过在 If I were you这样的表达中，通常还是以用were为宜。③ 有时条件从句用would表示愿意。如：If he would live on with me, I would be his better half. 要是他还愿意跟我过，我仍会做他的妻子。④ 对于与将来事实相反的情形，请注意以下几点。如：一是这里说的与将来事实相反，实为对将来情况的推测；二是此用法中的条件从句谓语除用过去式外，有时也用“should+动词原形”(表示可能性极小，常译为“万一”)或“were to+动词原形”(表示与将来事实相反的假设)；三是当条件从句使用“should+动词原形”这样的谓语时，主句谓语除可用“should (would, could, might)+动词原形”这样的虚拟语气外，也可用陈述语气或祈使语气。如：If it should rain tomorrow, don’t expect me. 万一明天下雨，就不要等我了。I should see him, I’ll tell him. 万一我见到他，我就告诉他。

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