Robert E. Park and Ernest W. Burgess thought that sociology had to move out of the nineteenth century, away from the speculations of William Graham Sumner, Lester Frank Ward, and Franklin H. Giddings, and into new, empirically testable terrain based on fieldwork and what came to be called "grounded theory". They had the great luxury of breadth, which for students at all levels in a great gift. Burgess wrote rough drafts, Park refined or rewrote them, and Burgess polished their commentaries, which were filled with admonitions to prospective social researchers. As Robert E. Lee Faris noted, "The entire treatment of human nature satisfactorily supported the main theme—human nature is a product of social living. Sociology was thereby freed from the excessive and unrewarding dependence regarding the subject on specialists in the field of biology". Fewer commentators have examined "The Green Bible" specifically, none with more insight than Faris, who followed his father through the Chicago graduate program.