What major theories explain employee motivation?

"Equity theory: A theory of motivation that holds that worker satisfaction is influenced by employees’ perceptions about how fairly they are treated compared with their coworkers. Expectancy theory: A theory of motivation that holds that the probability of an individual acting in a particular way depends on the strength of that individual’s belief that the act will have a particular outcome and on whether the individual values that outcome. Goal-setting theory: A theory of motivation based on the premise that an individual’s intention to work toward a goal is a primary source of motivation. Maslow’s hierarchy of needs: A theory of motivation developed by Abraham Maslow; holds that humans have five levels of needs and act to satisfy their unmet needs. At the base of the hierarchy are fundamental physiological needs, followed in order by safety, social, esteem, and self-actualization needs. Reinforcement theory: A theory of motivation that holds that people do things because they know that certain consequences will follow."