Eugene Johnsen (Chapter 9) also builds from a classic social psychological approach: Newcomb's A-B-X system. Somewhat akin to Breiger and Roberts' formulation, Johnsen's identifies nested, hierarchical structures with valued, directed ties between substructures. The approach centers around a set of shared thoughts and discourse among group members pertaining to valued interests, needs, persons, beliefs, etc. The strength of solidarity corresponds to the strength of the positive orientation of members to the central focus, and emerges through what Johnsen calls an agreement-friendship microprocess. Assumptions about the dispositional bases of tie-formations result in (or account for) the emergence of network substructures and patterns of ties among them. The strength of solidarity can then be measured by the strength and valence of ties within and between the substructures, and Johnsen offers some simple measures based on ratios of counts of signed directed ties. The approach distinguishes solidarity, which involves shared orientations or commitment to focal issues or persons, from social cohesion, which may result merely from interpersonal ties. This accords with Markovsky and Chaffee's (1995) inclusion of an objectified group element in the graph of the network to be analyzed. In our view, however, this element was neither necessary nor sufficient for the existence of group solidarity. In general, Johnson's work provides a valuable formalization of the process by which solidarity emerges within a particular theoretical domain, along with a set of simple indices for measuring solidarity within the range of outcomes that this process can generate.