Kohlberg (1927-1987) was a pioneer in the field of moral development. Influenced by Jean Piaget, he developed a large body of research investigating moral reasoning. Like Piaget, he was interested in intellectual development, in the way that the ability to reason changes across development. Kohlberg relied on a method of vignettes. He wrote up scenarios that involved a moral dilemma and presented them to his research subjects. His best known vignette involves a man named Heinz who broke into a pharmacy to steal a drug in order to save his wife’s life. Based on his research, Kohlberg divided moral development into three levels, pre-conventional, conventional, and post-conventional. Each level contains two stages, for a total of six stages altogether.

The first level, pre-conventional morality, is most commonly found in children under ten. In this level, morality is determined by the consequences of the action to the person performing the behavior—whether the individual is punished or rewarded. In the second level, conventional morality, the morality of a behavior is determined by its effect on social relationships. The third and final level is called post-conventional morality. In this stage, the person is interested in abstract concepts of justice and a just society. Kohlberg believed that all children go through the same sequence of stages in the same order. A fair amount of research supports this view for the first two levels, but the scientific evidence for the third level is much weaker. Kohlberg was also interested in moral reasoning in adults. Indeed, research has shown that different adults are characterized by different stages of moral development.