虚拟语气主要分为与现在事实相反，与过去事实相反以及与将来事实相反三个种类。英语虚拟语气三种形式常见用法如下：
1.表示与现在事实相反的情况
从句：If+主语+动词一般过去时(Be动词用were)
主句：主语+ should/would/might/could+do：
例句：
（1）If there were no air or water，there would be no living things on the earth.
如果没有水和空气，地球上就不会有生物。(事实：地球上既有空气也有水)
（2）If I had any money with me，I could lend you some.
如果我带钱了，我就会借给你些。（事实：没有带钱）
2.表示与过去事实相反的情况
从句：If+主语+had+done
主句：主语+should/would/might/could+have done
例句：If I had got there earlier，I should/would have met her.
如果我早到那儿，我就会见到她。（事实：去晚了）
3.表示与将来事实相反
从句：
①if+主语+were to do
②if+主语+should+do
③if+主语+动词一般过去式（be动词用were）
主句：主语+should/would/might/could+do
例句：If there were a heavy snow next Sunday，we would go skating.
如果下周日下大雪，我们就去滑冰。
