The inner workings of our own brains we feel to be uniquely worthy of investigation, but custom, we have a way of thinking, is behaviour at its most commonplace.
这是新概念4 lesson44中的句子。句中的most commonplace在这里是形容词最高级作名词作用吗?是因为前面的its所以名词化了吗?类似the+形容词名词化的用法?