What motivates humans to behave in certain ways has been an area of study for scholars for many centuries. As of 2011, there are six main theories of motivation. These modern theories take into account past theories presented by theorists such as Abraham Maslow. Motivation theories have been utilized to understand human behavior in work settings, educational endeavors and interpersonal relationships.

ERG Theory

Clayton Paul Alderfer, an American psychologist, proposed his ERG (Existence, Relatedness and Growth needs) Theory as redefining Maslow's need hierarchy motivational theory based on new empirical research. Alderfer's theory puts Maslow's need hierarchy into three short needs categories. His lowest-level needs are the existence needs, which include the need for basic human necessities. The next level of needs is the relatedness needs, which deal with a person's aspirations for the maintenance of interpersonal relationships, as well as a need for recognition and fame. The highest level of needs is the growth category, which is about an individual's need for self-development, advancement and personal growth.

McClelland's Theory of Needs

Psychological theorist David McClelland believed that human behavior is motivated by three needs: the need for power, achievement and affiliation. According to McClelland, the power need is based on a person's desire to influence others to his wishes. An individual's need for achievement is manifested through his need to excel and achieve a certain level of success. The need for affiliation concerns itself with the need to have positive interpersonal relationships.

Goal-Setting Theory of Motivation

The goal-setting theory of motivation was presented by Edwin Locke in the 1960s. In his theory, Locke links a person's goal-setting to performance of tasks. He alleges in his theory that a person's task performance is directly based on specific goals and the feedback he receives in pursuit of those goals. He further adds that a person's desire to work toward a specific goal is the main source of his motivation. The more specific and clear the goal, the better performance that can be expected. The goal-setting theory is used to increase an employee's incentive to meet the established goals.

Reinforcement Theory of Motivation

The reinforcement theory of motivation is often connected with B.F. Skinner. It states that past behavior, and the consequences of such behavior, affects future behavior in a cyclical learning pattern. In essence, the theory states that the resulting consequences (response) of previous behavior to a certain situation (stimulus) will dictate whether or not the individual chooses to repeat the same behavior in similar circumstances.

Equity Theory of Motivation

John Stacey Adams, a behavioral psychologist, developed the equity theory of motivation in relation to job motivation in 1963. He states that there are many variable factors that affect the relationship between employer and employee. He thought that a fair balance needed to exist between what the employee brings to the table and the compensation he receives for it. The balance between the two is what will ensure a positive, productive and motivated employee.

Expectancy Theory of Motivation

The expectancy theory was developed by Victor Vroom and differs completely from some of the theories based on needs. According to Vroom, it is the outcomes, not the needs of the individual, that serve as the motivating factors in determining the likelihood of a behavior. This theory states that there are two main areas that an individual assesses before engaging in the behavior. The first is the likelihood of completing the task. Then, a person assesses what the consequence or outcome of completing such a task will be.