One's capacity to act or to influence the behavior of others.
Power may be defined in both personal and interpersonal terms. In the first sense, it refers to one's physical, intellectual, or moral capacity to act. In the second, it denotes the ability to influence the behavior of others. Philosophers have often described power as an integral facet of human existence. Psychologist Harry Stack Sullivan (1892-1949) has claimed that power is a more crucial motivation than hunger or thirst.
Rollo May has written about power in terms of individual human potential, referring to the roots of the word "power" in the Latin word posse, which means "to be able." May distinguishes among five levels of intrapsychic power. The most basic level, the power to be, is literally the power to exist, which is threatened if one is denied the basic conditions of human sustenance. The second level, self-affirmation, goes beyond mere survival and involves recognition and esteem by others, while the third, self-assertion, refers to the more strenuous affirmation of one's existence that is required in the face of opposition. The next level of power, aggression, develops when one's access to other forms of self-assertion is blocked. In contrast to self-assertion, which May views as essentially defensive, aggression involves the active pursuit of power or territory. The endpoint in May's continuum of power is violence, which, unlike the other levels, is divorced from reason and verbal persuasion.
Power in its other sense—that of power over others—is a fundamental feature of all relationships, whether each party has a certain degree of power over the other (which is usually the case) or all the power resides with one party. Power may be based on force, acknowledged expertise, the possession of specific information that people want, the ability to reward others, or legitimization (the perception that one has the right to exercise it).
Other bases for power include identification with those who wield it and reciprocity (indebtedness to the wielder of power for providing a prior benefit of some sort). May has described various types of interpersonal power, ranging from harmful to beneficial: exploitative (characterized solely by brute force); manipulative (various types of power over another person); competitive (power against another); nurturing (power for another person); and integrative (power with another person).
May, Rollo. Power and Innocence: A Search for the Sources of Violence. New York: W. W. Norton, 1972.
Tillich, Paul. Love, Power, and Justice: Ontological Analyses and Ethical Applications. New York: Oxford University Press, 1960.