原帖请见：http://ask.yygrammar.com/q-27460.html

1. His absence from the graduation ceremony was the greatest regret in his life.

2. His failure to attend the graduation ceremony was the greatest regret in his life. （是否等于That he would not attend the graduation ceremony was the greatest in his life.）

3. His not attending the graduation ceremony was the greatest regret in his life. （是否等于That he had not attended the graduation was the greatest regret in his life. 或者 That he was absent from/did not attend the graduation ceremony was the greatest in his life. ）

4.It was the greatest regret in his life that he had been absent from the graduation ceremony.

5.It was the greatest regret in his life that he had not attended the graduation ceremony.

请教老师，句子1,2,3 的主语有何差别？句2中含有不定式的名词短语作主语所表示的动作是否发生在谓语动词was之后，即，毕业典礼还没到来，但是我们已经知道他在那一天不能来参加了，所以我们现在就下了结论，他不能来参加真是他一生最大的遗憾。句2是否等价于它后面括号里的句子？也就是说不定式在作后置定语和作状语时，用法有相同之处,都是发生在谓语之后的动作？

再看句2， 专家老师讲过动名词短语用于表达具体事件的时，动名词的动作和谓语时间同时或在谓语动词之前发生。所以句2是否表示毕业典礼发生了，他当时的确没来也发生了，事后我们下结论用was，如括号里第1个句子，与句4和句5时态一样。 或者就在举办典礼的时候，我们发现他缺席，于是当场下了结论。所以动名词的动作和谓语was同时发生。如括号里第2个句子。

关于句1中名词 his absence, 我们只知道有“他缺席”这个动作，至于发生于谓语之前还是之后，我们无法判断？

谢谢老师。