Some groups endure longer, are more stable, and are better able than other groups to incorporate new members or ideas without losing their distinctiveness. I present a simple model of individual behavior based on the thesis that interaction leads to shared knowledge and that relative shared knowlege leads to interaction. Using this model I examine the structural and cultural bases of group stability. Groups that are stable in the short run do not necessarily retain their distinctiveness in the long run as new members enter or new ideas are discovered. Consider two hypothetical high-tech consulting companies --Fairview and Taliesin --that specialize in designing medical information systems. Over the years, both companies have gained considerable expertise. Despite these similarities, however, the companies are quite different. Fairview was founded by six men, all graduates of BL Tech with degrees in business. The current members of the company get along well --they frequently hold Monday evening meetings and tend to have a unified perspective on how to develop systems. Taliesin resulted from a chance meeting in an airport between a computer science major and a business major interested in health care. Taliesin currently employs 12 men and women, who graduated from different universities and who represent a variety of disciplines. As at Fairview, the Taliesin employees get along well. Even so, they spend less time together than do Fairview employees, and often split into subgroups to handle multiple clients. Fairview and Taliesin thus represent very different sociocultural configurations: Fairview is small, socially undifferentiated, and culturally homogeneous; Taliesin is large, socially differentiated, and culturally heterogeneous. Various theories attempt to explain why some groups endure longer than others. These explanations usually suggest that favorable contexts are necessary for group stability, particularly when memberships change and new technologies and ideas emerge, and that highly differentiated contexts produce multiple groups. Such contexts frequently are characterized in terms of their environmental (Aldrich 1979; Hannan and Freeman 1977), institutional (Blau 1967; Collins 1975; Etzioni 1964; Sills 1957; Simmel [1908 ] 1955 ), ritual (Durkheim [1912 ] 1954 Goffman 1959; Mead [1934 ]1962 ), or functional (Aberle, Cohen, Davis, Leng, and Sutton 1950 Mack 1967; Parsons 1949 Parsons , 1951 characteristics, but rarely in terms as simple as "who knows what." Although these explanations tend to assume that groups members learn, interact, and communicate, the precise mechanisms underlying such processes are underspecified and the power of these fundamental "cognitive" mechanisms in producing and maintaining groups are ignored. In contrast to these context-dependent themes, I present a "constructural" perspective that is spare and highly general (see also Carley 1986a Carley , 1986bCarley , 1990 forthcoming a, forthcoming c) . According to this perspective, social change and stability result from changes in the distribution of knowledge as individuals interact and acquire and disseminate information. Constructuralism can be viewed as a modification of structural symbolic interactionism (Stryker 1980) in which knowledge mediates interaction and language, or it can be viewed as a modification of social differentiation theory (Blau 1977) in which knowledge mediates social dimensions (e.g., religion, sex, and age) and interaction. According to both theories, groups can be defined by shared social, demographic, or sociocultural features --e.g., Catholic boys age 13. According to the constructural perspective, each position on a social dimension is associated with a particular body of knowledge that is acquired by individuals with that characteristic --e.g., Catholics learn the tenets of Catholicism, the order of the mass, the holy days of obligation, and so forth. It is the wealth and uniqueness of the information associated with that dimension, not the dimension per se, that determines behavior. Constructural theory derives group characteristics and behavior from the Despite its simplicity, important and complex social behaviors emerge, many of which are consistent with existent empirical data. I use the model to explore group stability and endurance in one-group and two-group societies in which there is no change in group membership and no new ideas. I then examine the ability of these groups to assimilate a new member or idea without losing their uniqueness as a group. Finally, I discuss the model's scope, some important extensions to the model, and the role of simulation in this type of analysis.  The function u jk (t) chooses a fact randomly from all facts known by j; all facts known by j are equally likely to be chosen (see Carley 1990, App. 2, for additional details) . Adaptation. Within constructural theory, a second major premise is that individuals are continuously learning and that what they learn affects future behavior. For example, individuals generally acquire information that is communicated to them if they do not already have that information. In modeling this learning process, I assume that this occurs without error. Thus, an individual will know a fact during the next time period if he or she already knew the fact or if someone in the society communicated it to him or her. 3 This situation is represented as which means that there is: no forgetting (once an individual knows a fact, he or she always knows it); no discovery (if the individual "interacts with him/herself," as when Motivation. A third major premise of constructural theory is that relative
Similarity has its foundation on the sociological idea that friends tend to be alike REF .
A theory of group stability
American Journal of Sociology
Sociology