One of the million complications of thinking about this lecture is indeed to what extent it really is a significant departure from the work of structuralism.

1. is 是系动词，indeed 是副词修饰 is，“的确是”。

2. to what extent it really is a significant departure from the work of structuralism，是表语从句，结构上是名词性特殊疑问分句。也就是说，这个表语从句本身又是一个间接的特殊疑问句，由于做了名词性从句，故取名为 “名词性特殊疑问分句”。名称无所谓，你知道它是表语从句，由 what 引导，介词 to 提前就行了。

3. 特殊疑问句的例子：

To what extent are you willing to help me? 你愿意在多大程度上帮助我？ 

To what extent does she rely on you? 她在多大程度上依赖你？