Question

would have done是虚拟语气吗

would have done应该不仅仅指虚拟语气吧,是否应该还有推测的含义
如Born in better time,he would have done credit to society,这句如用虚拟语气,来解释与现在情况相反,似乎不通
再如she said that we would have finished the work by the end of this month
最后We would if we were taught to put the fish back when we were young.For we would have learned the truth

Answer 1

would have done有两种用法你都有提到：
1.虚拟语气：第一句 If born in better time,he...说明他“生不逢时”与
事实相反（最好前面加if)
第三句 We would if...说明“我们年轻时没有人教我们把鱼放回去”我们也
没有“学到这条真理”与事实相反.
2.在直接引语中的将来完成时改成过去时态的间接引语：你的第二句便是,
它的直接引语是
She said,"we will have finished the work by the end of this
month."