it have been necessary 和 it is necessary 的区别?请问下句中it had been necessary用现在时为何不行?
问题描述：
it have been necessary 和 it is necessary 的区别?请问下句中it had been necessary用现在时为何不行?
But rich planterswere few in the young county of Clayton,and,inorder to muster a full-strength troop,it had been necessary to raise more recruitsamong the sons of small farmers,hunters in the backwoods,swamp trappers,Crackersand,in a very few cases,even poor whites,if they were above the average oftheir class.
答
首先,这个故事讲的是过去的事情,所以be肯定不能用现在时,而必须用过去时.其次,如果用与陈述语态相同的时态,表示其发生（或出现）的时间与陈述语态所发生的时间大致相同（从语法角度考虑,此处是可以用过去时was的）；如果用过去完成时态,表示其发生（或出现）的时间比陈述语态所发生的时间更早,也就是相当于汉语的“早就需要...”.经你一说我感觉明白了。it had been necessary to raise......和if they were above the average of their class.不是所说的虚拟语气吧，曾有人告诉我说是虚拟语气。此处不是虚拟语态。