Psychologist Lawrence Kohlberg extended upon the foundation that Piaget built regarding cognitive development. Kohlberg believed that moral development, like cognitive development, follows a series of stages.

To develop this theory, Kohlberg posed moral dilemmas to people of all ages, and then he analysed their answers to find evidence of their particular stage of moral development.

The Heinz dilemma

In Europe, a woman was near death from a special kind of cancer. There was one drug that the doctors thought might save her. It was a form of radium that a druggist in the same town had recently discovered. The drug was expensive to make, but the druggist was charging ten times what the drug cost him to make. He paid $200 for the radium and charged $2,000 for a small dose of the drug.

The sick woman's husband, Heinz, went to everyone he knew to borrow the money, but he could only get together about $1,000, which is half of what it cost. He told the druggist that his wife was dying and asked him to sell it cheaper or let him pay later. But the druggist said: "No, I discovered the drug and I'm going to make money from it." So Heinz got desperate and broke into the man's store to steal the drug for his wife.

Stages of moral reasoning

After presenting people with a moral dilemma, Kohlberg reviewed people's responses and placed them in different stages of moral reasoning.

Kohlberg identified three levels of moral reasoning: pre-conventional, conventional, and post-conventional, where each level is associated with increasingly complex stages of moral development.

According to Kohlberg, an individual progresses from the capacity for pre-conventional morality (before age 9) to the capacity for conventional morality (early adolescence), and toward attaining post-conventional morality (once formal operational thought is attained), which only a few fully achieve.

Kohlberg placed in the highest stage responses that reflected the reasoning that Heinz should steal the drug because his wife's life is more important than the pharmacist making money. The value of a human life overrides the pharmacist's greed.

Moral reasoning is very different from moral behaviour

It is important to realise that even those people who have the most sophisticated, post-conventional reasons for some choices may make other choices for the simplest of pre-conventional reasons.

Many psychologists agree with Kohlberg's theory of moral development, but point out that moral reasoning is very different from moral behaviour.

Sometimes what we say we would do in a situation is not what we actually do in that situation. In other words, we might 'talk the talk,' but not 'walk the walk.'

How does this theory apply to males and females?

Kohlberg felt that more males than females move past stage four in their moral development. He went on to note that women seem to be deficient in their moral reasoning abilities.

These ideas were not well received by Carol Gilligan, a research assistant of Kohlberg, who consequently developed her own ideas of moral development. In her groundbreaking book, In a Different Voice: Psychological Theory and Women's Development, Gilligan criticised her former mentor's theory because it was based only on upper class White men and boys.

She argued that women are not deficient in their moral reasoning—she proposed that males and females reason differently. Girls and women focus more on staying connected and the importance of interpersonal relationships. Therefore, in the Heinz dilemma, many girls and women respond that Heinz should not steal the medicine.

Their reasoning is that if he steals the medicine, is arrested, and is put in jail, then he and his wife will be separated, and she could die while he is still in prison.