There are four theories, which explain why the groups are formed. These include:
1) Propinquity theory: quite often, individuals affiliate with one another because of spatial or geo-graphical proximity. In an organization, employees who work in the same area of the plant or office would more probably form into groups than those who are not physically located together. The propinquity theory explains a basic factor, i.e., proximity of people at the workplace, which leads to formation of groups. This phenomenon is observed in daily practice by all of us.
2) Homans' theory: according to George C. Homans, "the more activities persons share, the more numerous will be their interactions and the stronger will be their shared activities and sentiments; and the more sentiments persons have for one another, the more will be their shared activities and interactions". The homans theory has contributed a great deal to the understanding of group formation. It is based on three concepts, namely, activities, interactions and sentiments, which are directly related to each other as shown in figure aside. The members of a group share activities and interact with one member of a group share activities and interact with one another not just because of physical proximity, but also to accomplish group goals. They key element is interaction because of which they develop common sentiments for one another.
3) Balance theory: the theory as proposed by Theodore Newcomb states that "persons are attracted to one another on the basis of similar attitudes towards commonly relevant objects and goals. Once a relationship is formed, it strives to maintain a symmetrical balance between the attraction and the common attitudes. If an imbalance occurs, attempts are made to restore the balance. If the balance cannot be restored, the relationship dissolves". Both propinquity and interaction play a role in the balance theory. Thus, the balance theory is additive in nature in the sense that it introduces the factor of 'balance' to the propinquity and interaction factors. There must be a balance in the relationship between the group members for the group to be formed and for its survival. As shown in figure below, Mr. T will interact with Mr. n and form a group because of some common attitudes and values such as authority, work, life style, religion, politics, etc. they will strive to maintain a symmetrical balance between the attraction and the common attitudes. If they fail in their efforts, the group will get dissolved.
4) Exchange theory: this theory is based on reward -cost outcomes of interaction between people. To be attracted towards a group, a person thinks in terms of what he will get in exchange of interaction with the group members. Thus, there is an exchange relationship in terms of rewards and costs of associating with the group. A minimum positive level (rewards greater than costs) of an outcome must exist in order for attraction or affiliation to take place. Rewards form interactions gratify needs while costs incur anxiety, frustrations, embarrassment, or fatigue. Propinquity, interaction and common attitudes all have roles in the exchange theory.