According to sociologists, there are several different ways in which a person may become recognized as the leader of a social group. In the family, traditional cultural patterns confer leadership on one or both of the parents. In other cases, such as friendship groups, one or more persons may gradually emerge as leaders, although there is no formal process of selection. In larger groups, leaders are usually chosen formally through election or recruitment.
    Although leaders are often thought to be people with unusual personal ability, decades of research have failed to produce consistent evidence that there is any category of "natural leaders". It seems that there is no set of personal qualities that all leaders have in common; rather, virtually any person may be recognized as a leader if the person has qualities that meet the needs of that particular group.
    Research suggests that there are typically two different leadership roles that are held by different individuals. Instrumental leadership is leadership that emphasizes the completion of tasks by a social group. Group members look to instrumental leaders to" get things done". Expressive leadership, on the other hand, is leadership that emphasizes the collective well-beings of a social group's members. Expressive leaders are less concerned with the overall goals of the group than with providing emotional support to group members and attempting to minimize tension and conflict among them.
    Instrumental leaders are likely to have a rather secondary relationship to other group members. They give others and may discipline group members whoinhibit (阻碍) attainment of the group's goals. Expressive leaders cultivate a more personal or primary relationship to others in the group. They offer sympathy when someone experiences difficulties and try to resolve issues that threaten to divide the group. As the difference in these two roles suggest,expressive leaders generally receive more personal affection from groupmembers; instrumental leaders, if they are successful in promoting group goals,may enjoy a more distant respect.