The stages of moral development introduced by Lawrence Kohlberg constitute an adaptation of a psychological theory originally conceived by the Swiss psychologist Jean Piaget. Kohlberg began work on this topic in 1958 when he was a psychology graduate student at the University of Chicago. He expanded and developed this theory throughout his life. The theory holds that moral reasoning, the basis for ethical behaviour, has six identifiable developmental stages, each more adequate at responding to moral dilemmas than its predecessor.