【问】 What would I not have given to be able to say the rules without a mistake! (许国璋《英语》第2册，P.176)

请问这里为什么用虚拟语气?

【答】 动词不定式除了表示真实的条件之外，也可以表示与现在事实相反的虚拟条件和与过去事实相反的虚拟条件。当动词不定式表达与过去既成事实相反的虚拟条件时，句子的谓语动词要采用would(should)+完成时不定式。上面句子里的to be able to say...表达的就是与过去既成事实相反的假设：要是当时我能够一字不差地把这些规则说出来……(既成事实是：我未能一字不差地把这些规则说出来……)

1. She would have done anything to make amends.

要是当时能够赔偿的话，她是什么事都愿意干的。

2. When I was a teenager，I felt that I was just young and uncertain——that I was a newboy in a huge school，and I would have been very pleased to be regarded as something sointeresting as a problem. (NCE 4，L.6)

我十几岁时，总感到自己很小，茫然无知——就好象一所大学校里的新生。假如那时我被看作是一个难以对付的人物而惹人注目的话，那末，我是会感到非常得意的。

(to be regarded...表达的是一个与过去事实相反的假想条件)