Maslow argued that human needs could be characterized in terms of a hierarchy, which he modeled as an eight-layered pyramid. Each layer represents one type of human need that must be met (beginning at the bottom level) before the upper needs can be met. They are categorized into two groups: deficiency needs and growth, or being, needs. Deficiency needs can be thought of as physical and emotional needs, while growth needs are associated with intellectual and spiritual processes.
The bottom four characteristics of human needs are the deficiency needs. Beginning at the bottom are the physiological needs of hunger, thirst and others associated with the body. Above these is the need for safety, to be out of danger. Third up the scale is the need for love, belonging, acceptance and connectedness to others. The fourth rung on the pyramid is related to esteem needs, which include the need to be competent and to gain recognition and approval.
Once the deficiency needs are met, the growth needs can be pursued. Above the esteem needs is the need for knowledge and understanding. Next, at the sixth level are the aesthetic needs for symmetry, order and beauty. On the seventh level is what Maslow referred to as "self-actualization," meaning the pursuit of self-fulfillment and potential. The top growth need, and the smallest segment of the pyramid, is transcendence, the ability to transcend the ego and help others fulfill their potential.
In psychology, researchers usually study pathology, but Maslow focused his study on psychologically healthy people. He recognized certain common qualities that they exhibited, including their ability to be realistic and to accept the world as it is. Such well-adjusted individuals exhibit spontaneity, are problem-centered and autonomous, view the world with continued freshness and are capable of "peak experiences." Peak experiences are ecstatic states of being -- the sense of being fully alive and integrated with life. Self-actualization includes the sense of empowerment and being in control of one's own life -- complete emotional health.