过去虚拟语气如下：
1.与现在事实相反：条件句的谓语动词用一般过去式(be一般用were) ，主句谓语用would /should /could /might +动词原形。
如：
If I were you, I would never do that. 如果我是你,我决不做那件事。
If it weren’t for (=But for) your help, I would still be homeless. 若不是你帮忙，我现在还是无家可归。
If I had more money, I would buy a car. 我要是有再多一点钱，我就买汽车了。
注：在口语中，在第一、三人称后，也有人用was。如：
If I was(were) rich, I would buy a car. 我要是有钱，我就买汽车了。
2. 与将来事实相反：条件句中的谓语可用一般过去式、或者“were to /should＋动词原形”，主句谓语用would /should /could /might +动词原形。
如：
If it rained/should rain/were to rain tomorrow, I would not go there. 要是明天下雨，我就不去那里。
3. 与过去事实相反：条件句的谓语动词用过去完成式，主句谓语用would /should /could /might + have +过去分词。
如：
If he had taken my advice, he might not have made such a bad mistake. 要是他当初听从我的劝告就不会犯这么严重的错误了。
If it hadn’t been for Margaret, I might not have understood. 要不是有玛格丽特，我可能还不明白。