Lawrence Kohlberg (1927-1987) described three stages of moral development which described the process through which people learn to discriminate right from wrong and to develop increasingly sophisticated appreciations of morality. He believed that his stages were cumulative; each built off understanding and abilities gained in prior stages. According to Kohlberg, moral development is a lifelong task, and many people fail to develop the more advanced stages of moral understanding.
Kohlberg's first 'preconventional' level describes children whose understanding of morality is essentially only driven by consequences. Essentially, "might makes right" to a preconventional mind, and they worry about what is right in wrong so they don't get in trouble. Second stage 'conventional' morality describes people who act in moral ways because they believe that following the rules is the best way to promote good personal relationships and a healthy community. A conventional morality person believes it is wrong to steal not just because he doesn't want to get punished but also because he doesn't want his friends or family to be harmed. The final 'postconventional' level describes people whose view of morality transcend what the rules or laws say. Instead of just following rules without questioning them, 'postconventional' stage people determine what is moral based on a set of values or beliefs they think are right all the time. For example, during the Vietnam War, many Americans who were drafted to be soldiers opposed the war on moral grounds and fled to Canada rather than fight. Even though this behavior was against the law, these people decided that these particular laws did not follow the higher rules they believed in, and they chose to follow their higher rules instead of the law.