Kohlberg's theory proposes that there are three levels of moral development, with each level split into two stages. Kohlberg suggested that people move through these stages in a fixed order, and that moral understanding is linked to cognitive development. The three levels of moral reasoning include preconventional, conventional, and postconventional.

By using children's responses to a series of moral dilemmas, Kohlberg established that the reasoning behind the decision was a greater indication of moral development than the actual answer.

Lawrence Kohlberg (1958) agreed with Piaget's theory of moral development (1932) in principle but wanted to develop his ideas further. 

He used Piaget’s storytelling technique to tell people stories involving moral dilemmas.  In each case, he presented a choice to be considered, for example, between the rights of some authority and the needs of some deserving individual who is being unfairly treated.

One of the best known of Kohlberg’s (1958) stories concerns a man called Heinz who lived somewhere in Europe.

Heinz’s wife was dying from a particular type of cancer. Doctors said a new drug might save her. The drug had been discovered by a local chemist, and the Heinz tried desperately to buy some, but the chemist was charging ten times the money it cost to make the drug, and this was much more than the Heinz could afford.

Heinz could only raise half the money, even after help from family and friends. He explained to the chemist that his wife was dying and asked if he could have the drug cheaper or pay the rest of the money later.

The chemist refused, saying that he had discovered the drug and was going to make money from it. The husband was desperate to save his wife, so later that night he broke into the chemist’s and stole the drug.

1. Should Heinz have stolen the drug?

2. Would it change anything if Heinz did not love his wife?

3. What if the person dying was a stranger, would it make any difference?

4. Should the police arrest the chemist for murder if the woman died?

By studying the answers from children of different ages to these questions, Kohlberg hoped to discover how moral reasoning changed as people grew older. The sample comprised 72 Chicago boys aged 10–16 years, 58 of whom were followed up at three-yearly intervals for 20 years (Kohlberg, 1984).

Each boy was given a 2-hour interview based on the ten dilemmas. What Kohlberg was mainly interested in was not whether the boys judged the action right or wrong, but the reasons given for the decision. He found that these reasons tended to change as the children got older.

Kohlberg identified three distinct levels of moral reasoning:  preconventional, conventional, and postconventional. Each level has two sub-stages.

People can only pass through these levels in the order listed. Each new stage replaces the reasoning typical of the earlier stage. Not everyone achieves all the stages. The 3 levels of moral reasoning include:

Preconventional morality is the first stage of moral development, and lasts until approximately age 9. At the preconventional level children don’t have a personal code of morality, and instead moral decisions are shaped by the standards of adults and the consequences of following or breaking their rules.

For example, if an action leads to punishment is must be bad, and if it leads to a reward is must be good.

Authority is outside the individual and children often make moral decisions based on the physical consequences of actions.

• Stage 1. Obedience and Punishment Orientation. The child/individual is good in order to avoid being punished. If a person is punished, they must have done wrong.

• Stage 2. Individualism and Exchange. At this stage, children recognize that there is not just one right view that is handed down by the authorities. Different individuals have different viewpoints.

Conventional morality is the second stage of moral development, and is characterized by an acceptance of social rules concerning right and wrong. At the conventional level (most adolescents and adults), we begin to internalize the moral standards of valued adult role models.

Authority is internalized but not questioned, and reasoning is based on the norms of the group to which the person belongs.

A social system that stresses the responsibilities of relationships as well as social order is seen as desirable and must, therefore, influence our view of what is right and wrong.

• Stage 3. Good Interpersonal Relationships. The child/individual is good in order to be seen as being a good person by others. Therefore, answers relate to the approval of others.

• Stage 4. Maintaining the Social Order. The child/individual becomes aware of the wider rules of society, so judgments concern obeying the rules in order to uphold the law and to avoid guilt.

Postconventional morality is the third stage of moral development, and is characterized by an individuals’ understanding of universal ethical principles. These are abstract and ill-defined, but might include: the preservation of life at all costs, and the importance of human dignity.

Individual judgment is based on self-chosen principles, and moral reasoning is based on individual rights and justice. According to Kohlberg this level of moral reasoning is as far as most people get.

Only 10-15% are capable of the kind of abstract thinking necessary for stage 5 or 6 (post-conventional morality). That is to say, most people take their moral views from those around them and only a minority think through ethical principles for themselves.

• Stage 5. Social Contract and Individual Rights. The child/individual becomes aware that while rules/laws might exist for the good of the greatest number, there are times when they will work against the interest of particular individuals. 

The issues are not always clear-cut. For example, in Heinz’s dilemma, the protection of life is more important than breaking the law against stealing.

• Stage 6. Universal Principles. People at this stage have developed their own set of moral guidelines which may or may not fit the law. The principles apply to everyone.

E.g., human rights, justice, and equality. The person will be prepared to act to defend these principles even if it means going against the rest of society in the process and having to pay the consequences of disapproval and or imprisonment. Kohlberg doubted few people reached this stage.