Lawrence Kohlberg's stages of moral development constitute an adaptation of a psychological theory originally conceived by the Swiss psychologist Jean Piaget. Kohlberg began work on this topic as a psychology graduate student at the University of Chicago in 1958 and expanded upon the theory throughout his life.
The theory holds that moral reasoning, a necessary (but not sufficient) condition for ethical behavior, has six developmental stages, each more adequate at responding to moral dilemmas than its predecessor. Kohlberg followed the development of moral judgment far beyond the ages studied...