Understanding the meaning of need offers important insights not only to psychology but also to scholars of the social, pedagogical, economic and political sciences, among others. For this reason it has been studied and deepened by numerous disciplines. If in general we can say that a need is all that is necessary for an organism to survive and live a healthy life, we cannot however neglect that a definition of this type does not take into consideration the aspects related to the "higher" needs of being human, that is, those that are subjective and linked to the psychological sphere and to the realization of life rather than to its biological conservation. It is the needs that constitute the primary thrust towards action in the human being, to determine in which direction and for what purpose it moves. In a word, needs condition behaviors and it is for this reason that they have been at the center of psychological investigation from the very beginning. When we talk about needs, we generally start from Maslow's theory which proposed a hierarchy of human needs. Abraham Maslow, in his 1943 study entitled "A Theory of Human Motivation", introduces a universal theory, that is, applicable to all human beings, based on the concept of hierarchy of needs. This scale of needs is divided into five different levels, from the most basic (necessary for the survival of the individual) to the most complex (of a social nature). The individual is realized by passing through the various stages, which must be satisfied in sequence in order to progressively “climb” the pyramid towards the satisfaction of the most aspirational needs. This scale is internationally known as "Maslow's pyramid". Subsequently there was criticism of this identification scale, because it would drastically simplify man's real needs and, above all, their level of "importance." This theory, although fascinating and widely accepted in those years, and in a certain sense even today, has some limitations. For example, Maslow's work is based on a hierarchical vision that is culturally limited to the populations of the Western world. And again, his approach appears very rigid: the satisfaction of each need preludes that of the next need, not admitting that multiple needs receive satisfaction at the same time. For these reasons, after Maslow, other scholars have tried to refine his theory by integrating it into his most questionable points. For example Henry Alexander Murray, professor at Harvard and author of numerous studies on human personality based on the concept of need and external pressure, distinguishes needs into viscerogenic and psychogenic: the former correspond to the physiological and basic needs of the organism (generally considered primary and for this with a greater need for satisfaction); the psychogenic ones correspond to the specific needs of the specific psyche of each individual, which experiences and develops in the constant relationship with external stimuli (they are acquired throughout life). According to Murray's definition, a need can be described as "potentiality or readiness to respond in a certain way under certain given circumstances" (1938). Another attempt to overcome Maslow's theory is represented by Clayton P. Alderfer's ERG (Existence, Relatedness and Growth) Theory of Motivation (1969). This theory admits a greater degree of flexibility and movement of human needs which, in Alderfer's view, can be pursued simultaneously as well as varying in order in a subjective way. It is in this aspect that the most significant overcoming with respect to Maslow's theory is identified. According to the ERG theory, the 5 needs identified by Maslow are reduced to the following 3 categories: Existence - Existence Needs: concrete physiological needs (food, water, shelter) Relationship - Relatedness Needs: relational needs (emotional involvement in the family, friendships, work environment) Growth - Growth Needs: need for personal growth, self-realization and self-esteem In the field of studies on human needs and motivation, another important theory is proposed by David McClelland who, in his work entitled "The Achieving Society" argues that an individual's motivation is conditioned by three dominant needs:
Need for success (nACH),
Need for power (nPOW),
Affiliation need (nAFF)
