Kohlberg (1927–1987) was a pioneer in the field of moral development. Influenced by Piaget, he developed a large body of research investigating moral reasoning. Like Piaget, he was interested in the way that children reason, and how this changes across development. In fact, Piaget himself had studied the moral development of children, but in a fairly limited way. It was left to Kohlberg to create the more elaborate theory for which he is now known.

Kohlberg relied on a method of vignettes. He wrote up scenarios that involved a moral dilemma and presented them to his research subjects. He asked people what they would do in each situation and then asked them to explain the reasoning behind their decision. He was much more interested in the way that people reasoned about their moral choices than in their actual conclusions. Like Piaget, he was more interested in the thought process than the content. Kohlberg’s 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. (See Sidebar).