world was organized: into many dense groups with “weak ties” between them. Granovetter's work provided the theoretical background for Malcolm Gladwell's the Tipping Point. This line of research is still actively being pursued by Duncan Watts, Albert-László Barabási, Mark Newman, Jon Kleinberg and others. White's research on “vacancy chains” was assisted by a number of graduate students, including Michael Schwartz and Ivan Chase. The outcome of this was the book Chains of Opportunity. The book described a model of social mobility where the roles and the people that filled them were independent. The idea of a person being partially created by their position in patterns of relationships has become a recurring theme in his work. This provided a quantitative analysis of social roles, allowing scientists new ways to measure society that were not based on statistical aggregates. During the 1970s, White work with his student's Scott Boorman, Ronald Breiger, and Francois Lorrain on a series of articles that introduce a procedure called "blockmodeling" and the concept of "structural equivalence." The key idea behind these articles was identifying a "position" or "role" through similarities in individuals' social structure, rather than characteristics intrinsic to the individuals or a priori definitions of group membership. At Columbia, White trained a new cohort of researchers who pushed network analysis beyond methodological rigor to theoretical extension and the incorporation of previously neglected concepts, namely, culture and language. Many of his students and mentees have had a strong impact in sociology. Other former students include Michael Schwartz and Ivan Chase, both professors at Stony Brook; Joel Levine, who founded Dartmouth College's Math/Social Science program; Edward Laumann who pioneered survey-based egocentric network research and became a dean and provost at University of Chicago; Kathleen Carley at Carnegie Mellon University; Ronald Breiger at the University of Arizona; Barry Wellman at the University of Toronto and then the NetLab Network; Peter Bearman at Columbia University; Bonnie Erickson (Toronto); Christopher Winship (Harvard University); Joel Levine (Dartmouth College), Nicholas Mullins (Virginia Tech, deceased), Margaret Theeman (Boulder), Brian Sherman (retired, Atlanta), Nancy Howell (retired, Toronto); David R. Gibson (University of Notre Dame); Matthew Bothner (University of Chicago); Ann Mische (University of Notre Dame); and Kyriakos Kontopoulos (Temple University). Selected books Harrison C. White (2008), Identity and Control: How Social Formations Emerge (Second Edition), Princeton, NJ: Princeton University Press Harrison C. White (2002), Markets from Networks: Socioeconomic Models of Production, Princeton, NJ: Princeton University