Psychological egoism is the monist theory that all human motivation is egoistic—what one desires for oneself or is in one's self-interest. Psychological altruism is the pluralistic theory that some human motivations are altruistic—what is best for others. Monist motivational theory is often criticized as being overly reductive or abstract. It takes only one example of altruistic motivation to reject psychological egoism. Furthermore, some motivations may be neither egoistic nor altruistic.

Monist motivational theory views humans as economic beings, with monetary reward the driving motivation for behavior. It is an egoistic theory, because it argues that effective motivation is based solely on individual rewards rather than group rewards. It also postulates that motivation is strongest if monetary reward follows immediately from the effort—daily or weekly paydays rather than monthly salaries and end-of-the-year bonuses—and that the amount of effort is directly related to the size of the monetary reward.

Frederick Winslow Taylor (1856–1915) was the most influential proponent of monist motivational theory. In The Principles of Scientific Management Page 770  |  Top of Article(1911) and other publications, Taylor argued that workers have no motivation other than pay. Therefore, production should be broken down into small tasks; workers should be trained to complete a specific small task as efficiently as possible, and workers should be paid according to the number of items produced in a period of time. Thus, maximizing productivity maximizes worker pay and, therefore, maximizes worker motivation. Taylor's approach was widely adopted in the early twentieth century, most famously on the automobile assembly line.

Taylor's theory was criticized for being overly simplistic and ignoring socio-psychological and other motivating factors. It was ultimately discredited as oppressive to workers. However, traditional or classical management theory is based in monist motivational theory: once primary physiologic needs—food, shelter, safety, and security—are met, economics is the main motivating force.

Elton Mayo (1880–1949) developed one of the first pluralistic theories of workplace motivation. He conducted experiments on the effects of lighting and other working conditions on the productivity of female workers at the Hawthorne factory of the Western Electric Company in Chicago. To his surprise, even under worsening conditions, productivity remained the same or improved. This was because the women were consulted about the changes and provided feedback—it was human interaction that influenced worker motivation and productivity; in addition to pay, workers were motivated by their social needs. Mayo concluded that rather than the autocratic supervisors of Taylor's system, the best motivators were team work and communication and interaction between managers and workers.

In the mid-twentieth-century United States, the pluralistic motivational theories of the humanist behaviorist psychologists Abraham Maslow (1908–1970) and Frederick Irving Herzberg (1923–2000) came to dominate management science. Maslow's hierarchy of needs defined five basic categories: lower-order needs were for physiologic necessities, safety and security, and social/ affection; higher-order needs were for esteem—including mastery, achievement, recognition, and approval— and self-actualization. Maslow's general theory of motivation stated that once needs are met, they cease to be motivators of behavior.

Herzberg's two-factor or motivation-hygiene theory of job satisfaction and motivation elaborated on Maslow's hierarchy of needs. “Hygiene” referred to extrinsic factors corresponding to Maslow's lower-order needs—pay, working conditions, safety, and benefits—that, if absent, are demotivating and result in job dissatisfaction. These are “hygienic” in the sense of being preventative but do not contribute to job satisfaction. Motivators are intrinsic factors, including a sense of accomplishment, pride in one’ work, recognition for accomplishments, and increased responsibilities, that increase motivation and job satisfaction.

Modern management theories are generally based on the pluralistic motivational theories of Maslow, Herzberg, and others: Once basic human needs have been satisfied, participation, achievement, and recognition are major motivating factors.