在英语语法中，虚拟语气用于表达与现实情况不一致的情况。根据时间的不同，虚拟语气的表达方式也有所区别。以下是虚拟语气的几种常见应用：

1. 表达与现在事实相反的假设时，使用"if + did / were + ..., ... would/ should/ could/ might + do"的结构。例如："If I were you, I would go abroad at once."（我不是你，但如果是你的话，我会立刻出国）。

2. 与过去事实相反的假设中，使用"if + had done + ..., ... would (might) have done ..."的结构。例如："If I had known your telephone number yesterday, I would have phoned you."（我昨天如果知道你的电话号码，就会给你打电话）。

3. 与将来事实相反的假设中，有两种情况。一种是"if + should + v., ... would + v."，表示可能性较小，译作“万一”（例如："If it should rain tomorrow, you could stay at home."）。另一种是"if + did / were to + v ..., would + v."，表示完全不可能（例如："If you finished it in 3 minutes, I would give you my car."）。

在特定情况下，虚拟语气的使用有其特殊性。例如，某些动词后跟的宾语从句需用"should + 动词原形"（在美国英语中"should"可省略）的形式（如："He suggested that we (should) help them with English."）。某些名词后的同位语从句也需要使用"should + 动词原形"的形式（如："He made a suggestion that we (should) have a fancy dress party."）。还有像"It is / was important / necessary / natural / essential / advisable / strange / surprising, ect. + that +主语+ should + v."这样的句型（如："It is strange that you should say such a thing."）。在wish后的宾语从句、as if后的状语从句中，使用"主 + wish+ (that) + 主 + did / were（指现在）/ had done（指过去）/ would+ v.（指将来）"的形式（如："I wish that I could meet my uncle tomorrow."）。在"It is (high) time that ... + did / were ..."这样的句型中，使用"did / were"的形式（如："It is time that you went to bed."）。还有"would rather that ... + did / were ..."（如："I would rather that you were not here now."）和"would sooner that ... + did / were ..."（如："I would sooner that you got up earlier."）这样的表达方式。