In the social sciences, social groups can be categorized based on the various group dynamics that define social organization. In sociological terms, groups can fundamentally be distinguished from one another by the extent to which their nature influence individuals and how. A primary group, for instance, is a small social group whose members share close, personal, enduring relationships with one another (e.g. family, childhood friend). By contrast, a secondary group is one in which interactions are more impersonal than in a primary group and are typically based on shared interests, activities, and/or achieving a purpose outside the relationship itself (e.g. coworkers, schoolmates). Four basic types of groups have traditionally been recognized: primary groups, secondary groups, collective groups, and categories. Primary and secondary groups The distinction between primary and secondary groups serves to identify between two orders of social organization. Primary groups A primary group is typically a small social group whose members share close, personal, enduring relationships in which one exchanges implicit items, such as love, caring, concern, support, etc. These groups are often long-lasting and marked by members' concern for one another, where the goal is actually the relationship themselves rather than achieving another purpose. In general, they are also psychologically comforting to the individuals involved, providing a source of support. As such, primary groups or lack thereof play an important role in the development of personal identity, and can be understood as tight circles composed of people such as family, long-term romances, crisis-support group, church group, etc. The concept of the primary group was first introduced in 1909 by sociologist Charles Cooley, a member of the famed Chicago school of sociology, through a book titled Social Organization: A Study of the Larger Mind. Although Cooley had initially proposed the term to denote the first intimate group of an individual's childhood, the classification would later extend to include other intimate relations. Additionally, three sub-groups of primary groups can be also identified: Kin (relatives) Close friends Neighbours Secondary groups (social groups) A secondary group is a relatively larger group composed of impersonal and goal-oriented relationships, which are often temporary. These groups are often based on achieving a common purpose outside of the relationship itself and involve much less emotional investment. Since secondary groups are established to perform functions, individual roles are more interchangeable, thus members are able to leave and outgroup are able to join with relative ease. Such groups