actions speak louder than words but not nearly as often

问题描述:

actions speak louder than words but not nearly as often
在这句话中,but后面充当什么成分?

很明显but表示转折,引出下面的内容,就是介词成分.难道楼主认为是主语吗!
就像and这样的连词一样,前后的主语都是actions~