虚拟语气倒装当虚拟条件句中含有were，had，should，could等动词时，可以将if省略，然后将were，had，should，could 等词移至句首。
例如：
①If he should fail, he would kill himself. →Should he fail, he would kill himself. 万一失败，他就会自杀。
②If I were you, I would do it at once. →Were I you, I would do it at once. 假若我是你，我就会马上做。
③If I could do it, I would. →Could I do it, I would. 要是我能做此事，我一定会做。
④If he had seen you yesterday, he would have asked you about it. →Had he seen you yesterday, he would have asked you about it. 他昨天要是看到了你，他就会问你这事了。