Clayton Paul Alderfer is an American psychologist who developed Maslow’s hierarchy of needs into a theory of his own. Alderfer’s ERG theory suggests that there are three groups of core needs: existence (E), relatedness (R), and growth (G)—hence the acronym ERG. These groups align with Maslow’s levels of physiological needs, social needs, and self-actualization needs, respectively.

“Existence” needs concern our basic material requirements for living. These include what Maslow categorized as physiological needs (such as air, food, water, and shelter) and safety-related needs (such as health, secure employment, and property).

“Relatedness” needs have to do with the importance of maintaining interpersonal relationships. These needs are based in social interactions with others and align with Maslow’s levels of love/belonging-related needs (such as friendship, family, and sexual intimacy) and esteem-related needs (gaining the respect of others).

Finally, “growth” needs describe our intrinsic desire for personal development. These needs align with the other portion of Maslow’s esteem-related needs (self-esteem, self-confidence, and achievement) and self-actualization needs (such as morality, creativity, problem-solving, and discovery).

Alderfer proposed that when a certain category of needs isn’t being met, people will redouble their efforts to fulfill needs in a lower category. For example, if someone’s self-esteem is suffering, he or she will invest more effort in the relatedness category of needs.