if引导的虚拟语气应该用什么时态？

Question

如题所述

Answer 1

1. 表示与现在事实相反的情况，其句型为“ if+ 主语 + 动词的过去式（ be 动词用 were ），主语 +would / could / might / should + 动词原形”。如：
If the weather were fine, we would go to Shanghai.
如果天气好，我们就去上海。（事实上天气不好）
If they had time, they would / could / might go with me.
如果他们有时间，他们就会（可能）和我一起去。
2. 表示与过去事实相反的情况。其句型为“ if + 主语 + 动词的过去完成式，主语 +would / could / should / might + have + 动词的过去分词”。如：
If I had taken his advice, I shouldn't / wouldn't / couldn't have made such a mistake.
如果我按照他的建议去做，我一定不会（不可能）犯这样的错误。
3. 表示与将来事实可能相反的假设和结果，其句型为“ if + 主语 + 动词的过去式 / should + 动词原形 / were to +动词原形，主语 +would / could / might / should + 动词原形”。如：
The glass would break if you dropped it.
杯子摔下来会打破的。（事实上没有摔下来）
If it should rain, the crops would / could / might be saved.
假如天下雨，庄稼就一定（有可能）会得救。

Answer 2

1、对现在情况的假设：表示说话时不存在或与事实相反的情况.形式：If+主语+did,主语+should/ would /could +do.例句：If you knew english well,you would be able to talk with foreigners freely.
2、对过去情况的假设：表示与过去事实相反的情况.形式：if+主语+had done,主语+should/would /could+have done.例句：if i had not studied hard ,i might have failed in the exam.（事实是我通过考试了）
3、对将来情况的假设：表示将来实现可能性不大的情况.形式：if+主语+did/were to do /should do,主语+should /would /could do.例句:if he should change his mind ,what would we do?