1. 虽然imagine属于否定转移的动词，但... people could not imagine that there would ever be a time when...一句中不存在否定转移现象。因为could not imagine that there would ever be a time when...和could imagine that there would notever be a time when...意思完全不同。简单说就是：情态动词could阻碍了否定的转移。

2. ever多用于否定句、疑问句和条件句等。用于肯定句中很少见，例如：We had heard a lot about her before weever met her.  但需要澄清的关键是：“ever通常限于非肯定句”只是一个简便但并非严密的说法。实际上应该理解为：非肯定词ever一般用于非肯定语境。其中重要的一条就是：ever可用在与具有非肯定意义的动词、介词、形容词、副词和名词等相关的结构（尤以补语为多）中。所以，在...people could not imagine that there would ever be a time when..一句中，虽然that从句本身并非否定句，但ever处于主句的could not之后，属于其否定范围之内，ever用法正常。

3. 适用否定转移的动词很多，一类与认知或观点相关，例如think, suppose, believe, expect, figure, imagine等等。但同一语义域的hope, assume, wish(接从句时)不能否定转移；另一类与感知相关的系动词，如appear, seem, feel, look, sound等。详情参阅英语语法参考书。这些否定转移的结构，其否定词也可以留在从句中，通常情况下意思没有区别。例如I don’t think you understand和I think you don’t understand两句通常同义，但第一句更普遍。