Mary Douglas is an outstanding example of an evaluative thinker at work. In Purity and Danger: An Analysis of Concepts of Pollution and Taboo, she delves in great detail into existing arguments that portray traditional societies as "evolving" from "savage" beliefs in magic, to religion, to modern science, then explains why she believes those arguments are wrong. She also adeptly chaperones readers through a vast amount of data, from firsthand...