Although trait, behavioral, and contingency approaches have each contributed to the understanding of leadership, none of the approaches have provided a completely satisfactory explanation of leadership and leadership effectiveness. Since the 1970s, several alternative theoretical frameworks for the study of leadership have been advanced. Among the more important of these are leader-member exchange theory, transformational leadership theory, the substitutes for leadership approach, and the philosophy of servant leadership.

LEADER-MEMBER EXCHANGE THEORY.

Leader-member exchange (LMX) theory was initially called the vertical dyad linkage theory. The theory was introduced by George Graen and various colleagues in the 1970s and has been revised and refined in the years since. LMX theory emphasizes the dyadic (i.e., one-on-one) relationships between leaders and individual subordinates, instead of the traits or behaviors of leaders or situational characteristics.

The theory's focus is determining the type of leader-subordinate relationships that promote effective outcomes and the factors that determine whether leaders and subordinates will be able to develop high-quality relationships.

According to LMX theory, leaders do not treat all subordinates in the same manner, but establish close relationships with some (the in-group) while remaining aloof from others (the out-group). Those in the in-group enjoy relationships with the leader that is marked by trust and mutual respect. They tend to be involved in important activities and decisions. Conversely, those in the out-group are excluded from important activities and decisions.

LMX theory suggests that high-quality relationships between a leader-subordinate dyad will lead to positive outcomes such as better performance, lower turnover, job satisfaction, and organizational commitment. Empirical research supports many of the proposed relationships (Steers et al., 1996).

TRANSFORMATIONAL LEADERSHIP THEORIES.

Beginning in the 1970s, a number of leadership theories emerged that focused on the importance of a leader's charisma to leadership effectiveness. Included within this class of theories are House's theory of charismatic leadership, Bass's transformational leadership theory, and Conger and Kanungo's charismatic leadership theory.

These theories have much in common. They all focus on attempting to explain how leaders can accomplish extraordinary things against the odds, such as turning around a failing company, founding a successful company, or achieving great military success against incredible odds. The theories also emphasize the importance of leaders' inspiring subordinates' admiration, dedication, and unquestioned loyalty through articulating a clear and compelling vision.

Tranformational leadership theory differentiates between the transactional and the transformational leader. Transactional leadership focuses on role and task requirements and utilizes rewards contingent on performance. By contrast, transformational leadership focuses on developing mutual trust, fostering the leadership abilities of others, and setting goals that go beyond the short-term needs of the work group.

Bass's transformational leadership theory identifies four aspects of effective leadership, which include charisma, inspiration, intellectual stimulation, and consideration. A leader who exhibits these qualities will inspire subordinates to be high achievers and put the long-term interest of the organization ahead of their own short-term interest, according to the theory. Empirical research has supported many of the theory's propositions.

SUBSTITUTES FOR LEADERSHIP THEORY.

Kerr and Jermier introduced the substitutes for leadership theory in 1978. The theory's focus is concerned with providing an explanation for the lack of stronger empirical support for a relationship between leader traits or leader behaviors and subordinates' satisfaction and performance. The substitutes for leadership theory suggests that characteristics of the organization, the task, and subordinates may substitute for or negate the effects of leadership, thus weakening observed relationships between leader behaviors and important organizational outcomes.

Substitutes for leadership make leader behaviors such as task-oriented or relationship-oriented unnecessary. Characteristics of the organization that may substitute for leadership include formalization, group cohesiveness, inflexible rules, and organizational rewards not under the control of the leader. Characteristics of the task that may substitute for leadership include routine and repetitive tasks or tasks that are satisfying. Characteristics of subordinates that may substitute for leadership include ability, experience, training, and job-related knowledge.

The substitutes for leadership theory has generated a considerable amount of interest because it offers an intuitively appealing explanation for why leader behavior impacts subordinates in some situations but not in others. However, some of its theoretical propositions have not been adequately tested. The theory continues to generate empirical research.

SERVANT LEADERSHIP.

This approach to leadership reflects a philosophy that leaders should be servants first. It suggests that leaders must place the needs of subordinates, customers, and the community ahead of their own interests in order to be effective. Characteristics of servant leaders include empathy, stewardship, and commitment to the personal, professional, and spiritual growth of their subordinates. Servant leadership has not been subjected to extensive empirical testing but has generated considerable interest among both leadership scholars and practitioners.

Leadership continues to be one of the most written about topics in the social sciences. Although much has been learned about leadership since the 1930s, many avenues of research still remain to be explored as we enter the twenty-first century.