什么是虚拟语气及它的时态用法：

虚拟语气是英语中用来表示假设、愿望、猜测、比喻或决定、主张、要求、建议和命令等情态的一种语气。它多用于以下一些情况：

一、在由if引导的非真实条件状语从句中：

1. 现在虚拟：假设的条件不符合现在的实际情况。主句谓语用would (could, should, might)+动词原形，从句谓语用动词过去式(be用were)。例如：

- We could ask the teacher if he were here now. (如果老师此时在这儿的话，我们就可以问他了。)

- If he were not ill in bed, he might come to class. (如果他没有病倒在床的话，他会来上课的。)

2. 过去虚拟：假设的条件不符合过去的实际情况。主句谓语用would (could, should, might)+have+动词过去分词，从句谓语用had +动词过去分词。例如：

- I hadn't forgotten your telephone number, I should have called you last Sunday. (我要是没有忘记您的电话号码，上周日我就给你打电话了。)

- Should it (Were it to) rain, the crops would be saved. (如果天下雨，庄稼就会得救。)

3. 将来虚拟：假设的条件不可能符合将来的实际情况。主句谓语用would (could, should, might)+动词原形，从句谓语用动词过去式(be用were)，也可用were+to+动词原形，或用should+动词原形。例如：

- If I were to do it again tomorrow, I might do it in different ways. (要是我明天再做一遍，我可能会用不同的方式去做。)

- If there should be no water, there would be no life on earth. (要是没水，地球上是不会有生命的。)

二、倒装虚拟句（只能与过去/将来事实相反，省去if，只有三种倒装形式）：

- Had I had enough money, I would have bought a book. (如果我当时有足够的钱，我就会买一本书。)

- Were I to have enough money, I would buy a book. (如果我现在要有足够的钱，我就会买一本书。)

- Should I have enough money, I would buy a book. (如果将来我有了足够的钱，我就会买一本书。)

三、混合时间虚拟语气（主要是抓住时间状语）：

- If I had studied English at school, I could read the English novel now. (对过去事实虚拟+对现在事实虚拟)

- Were you to drive, she wouldn't have missed the film last night. (对现在事实虚拟+对过去事实虚拟)

四、含蓄虚拟条件句即指将条件从句隐藏在上下文一定的短语中的一类条件句。如：otherwise, but for, without, or等引起的短语。

- Without electricity human life would be quite different today. (如果没有电，人类的生活今天就会非常不同。)

- He was very busy yesterday, otherwise he would have come to the meeting. (他昨天非常忙，否则他就会来参加会议了。)

以上是对虚拟语气的简要说明和用法，希望对您有所帮助。