he novel has been being written for ages now”，它是“I have been writing the novel for ages now”的被动形式。 在直陈语气之外，完成体只有有限的真正存在。因为英语情态动词很大程度上是变化不完全动词，并且因为英语虚拟语气自身不形成真正的过去时，动词“to have”经常用来构造过去时态。例如，尽管“I could write a novel”在英语中是允许的，“I could wrote a novel”是“不合语法的”