首先同意四楼对一楼的评价.
approach to 是固定搭配,to这里是介词,后面接名词,动名词.
scaling the degree to which they can be described by different trait
与classifying people into a limited number of distinct types 是并列关系,中间有连接词and,因此二者共同的动词是 involve.
整个句子的主语是Two of the oldest approaches
谓语是involve
involve后面的整一个是宾语,
其中scaling the degree to which they can be described by different trait 中的to which they can be described by different trait是状语从句,意为"到...程度".
整个句子的意思是:其中两种最古老的描述个性的方法包括,一是把人分成有限的几种能加以区别的类型,二是根据不同特质对个性的描述程度划分不同等级.