什么叫虚拟语气在英语中请英语高手详细说明

虚拟语气
结构 条件句 主句
现在 过去式 be用 were should
过去 had done should / would have done
将来 did / should /were to should / would do

If I had money now, we should buy it without a moment’s hesitation.
If you had attended the wedding ceremony yesterday, you would have met Jam.
If you dropped the vase, it would break into pieces.
注：
(1) if 省略
Were he in my position, he would do the same.
Had it not been for / Were it not for (如果没有) their help, we wouldn’t have overcome these difficulty
(2) 混合虚拟
If I had asked her for advice yesterday, I should know what to do now.

(3) 含蓄虚拟 (otherwise ,without ,but for)
Without air, there would be no living things.
But for your help we couldn’t have succeeded in the contest.
(4) 虚拟语气在宾语从句中的运用 (should可省略)
相关动词：ask , desire , demand , advise , suggest（建议） , require , request , insist（坚持要