用的是虚拟语气,省略和倒装三种语法结构.前一句可改为 If he had lived longer.如果他（过去）能活得更久一点的话,表示与过去事实相反的虚拟.因为从句中用had可以把它提到句首.省略should.可以解释的再具体些吗？比如：1.如果前半句原型是If he had lived longer，那你说should省略了，这个should是哪里的呢？原句中并没有啊。2.If he had lived longer，这个为什么不是条件状语从句呢？给你以下例子If I had listened to our teacher carefully, I would have worked out the math problem yesterday.=Had i listened to ,,,,,If I were you ,I would go there at once.=Were I you, I would,,,.,If it should rain tomorrow, we would stop our sports meeting.=should it rain tomorrow,,,,以上三种和你问的一样。也就是说在if的虚拟句中如有had. should 和were就可以把它们提前（即倒装）省略引导词if。这是省略。同时这种情况都是在虚拟句中才能有的，所以这是三种语法的结合。为什么把had. should 和were提前后需要倒装呢？ if 引导的虚拟句属于状语从句的一种吗？谢谢你哦是状语从句，以上那些例子可以变为倒装也可不变。但是根据英美人习惯是常变的，那样比较地道。