In Jean Piaget's theory of cognitive development, he identified four stages that humans go through as they develop mentally. The sensorimotor stage is from birth to 2 years old when a child uses its reflexes and innate tendencies to adapt to its environment. The second stage is the preoperations stage from 2 to 7 years old when the child is egocentric and operates primarily using its intuitions, since logical thought processes are not yet developed. Seven- to 11-year-olds are in the concrete operations stage in which their intelligence uses both symbolic and logical faculties, under the governance of rules and regulations. The final stage occurs between 11 to 16 years old when abstract thinking develops and they are able to test their hypotheses.
Various types of stage theories have been recognized by psychologists and sociologists that define the different stages of learning that humans undergo. Eric Erickson's theory relates to the stages we pass through when we learn self-esteem and trust. J.A. Devito's relationship theory delineates the stages apparent when establishing and dissolving relationships. James Fowler established a stage theory of how religious faith is developed in a person, while Lawrence Kohlberg defined one that shows the process of value and moral development.
The Levinger Relationship Stage Theory defines five stages relationships undergo. The first stage is acquaintance or attraction, in which people meet and are attracted to someone for various reasons. The second stage is known as the buildup stage as in this one the parties involved reveal more about themselves to each other. The third stage encompasses continuation and consolidation during which long term commitments are made. The fourth stage exhibits the deteriorization of the relationship due to various factors, with the final stage ending the relationship when those involved agree to go their separate ways.
Elisabeth Kubler-Ross identified similar stages people undergo when faced with death and dying. Dying people undergo fives stages when faced with their own demise: denial, anger, bargaining, depression and acceptance. Close relatives, friends and caregivers may also experience the same stages as the person facing imminent demise.