Forsyth's 5 theories (pp. 45-51)

Motivational:

Members satisfy needs and pursue goals (own, group's) in groups

Behavioral:

Groups shape member behavior by providing rewards and costs

Systems:

The interaction of members results in emergent, group-level behavior

Cognitive:

People process information about one another and about group tasks

Biological:

Social behavior in groups is shaped by evolutionary history

Another way of classifying theories is the six metaphors (McGrath, 1997). Connections to Forsyth's system are presented in parentheses.

Six metaphors: Groups as:

vehicles for influencing members (behavioral)

systems for patterning human interaction (systems)

vehicles for task performance (motivational-goals)

information processing systems

(cognitive)

consensus and conflict-managing systems (doesn't connect to Forsyth--Political)

systems for regulating, motivating, coordinating behavior

(motivational, behavioral)

McGrath, J. E.(1997). Small group research, that once and future field: An interpretation of the past with an eye to the future. Group Dynamics: Theory, Research, and Practice, 1, 1-27.