在英语语法中，虚拟语气是一种用来表达假设、愿望、建议或可能性的语言形式。它通常用于描述与事实不符的情况或不可能实现的愿望。为了更好地理解和掌握虚拟语气的使用方法，我们可以将其分为三种主要的时态：现在时、过去时和将来时。下面将通过一个表格来详细展示这三种时态下的虚拟语气用法。

| 时态 | 条件从句（if引导）| 主句 |

|------------|-------------------------------------------|--------------------------------------------------|

| 现在时 | If + 主语 + 动词原形 | 主语 + would/could/might + 动词原形|

|| 示例：If I had time, I would go to the park.| 示例：If you studied harder, you could pass the exam. |

| 过去时 | If + 主语 + 过去完成时（had + 过去分词）| 主语 + would/could/might + have + 过去分词|

|| 示例：If he had known about it, he wouldn't have come. | 示例：If we had booked earlier, we might have got better seats. |

| 将来时 | If + 主语 + should/were to + 动词原形 | 主语 + would/could/might + 动词原形|

|| 示例：If it should rain tomorrow, we would stay at home. | 示例：If they were to arrive late, we would start without them. |

以上表格清晰地展示了虚拟语气在不同时间背景下的结构特点。需要注意的是，在实际应用中，虚拟语气的形式可能会根据具体语境有所变化，但其核心功能始终是为了表达一种非现实的情景或期望。通过反复练习和观察例句，可以逐渐提高对这一语法现象的理解和运用能力。