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Kohlberg proposed that moral reasoning develops through three levels, each with two stages: preconventional (obedience/punishment and self-interest), conventional (interpersonal conformity and law-and-order), and postconventional (social contract and universal ethical principles). Using moral dilemmas (the Heinz dilemma), Kohlberg argued that the stage of reasoning — not the conclusion reached — determines moral maturity. Higher stages require the cognitive capacity of formal operations and greater perspective-taking ability. Research confirmed an invariant sequence across cultures, though most adults reason at the conventional level.
Apply all six stages to the same Heinz dilemma to see how the same action (stealing medicine) is justified with qualitatively different reasoning. Then evaluate where different real-world moral arguments fall.
Kohlberg's theory asks a deceptively simple question: as people develop, does their moral reasoning change in a qualitative way — not just in content but in structure? His answer was yes, and he mapped out a six-stage sequence that describes how people understand the basis of moral rules at different points in development.
The three levels are defined by what makes something "right." At the preconventional level (Stages 1 and 2), morality is entirely external — right means avoiding punishment (Stage 1) or getting what you want while avoiding personal costs (Stage 2). The child at this level doesn't yet have an internalized sense of social norms; morality is about consequences to oneself. At the conventional level (Stages 3 and 4), the individual has internalized social norms and evaluates actions by whether they meet others' expectations (Stage 3: "being a good person") or uphold law and social order (Stage 4). Most adults reason at this level — rules are real and binding because they hold society together. At the postconventional level (Stages 5 and 6), the person can step outside society's rules and ask: are these rules themselves just? Stage 5 recognizes that social contracts can be renegotiated for the greater good; Stage 6 appeals to universal ethical principles (like Kant's categorical imperative) that transcend any particular society's laws.
The Heinz dilemma — a man must decide whether to steal a drug he cannot afford to save his dying wife — is Kohlberg's diagnostic tool. Notice that the dilemma is designed to force a conflict between law (do not steal) and life (save his wife). Kohlberg was not interested in what people decided, only in why. "He should steal it because people would think badly of him if he didn't" (Stage 3) and "he should steal it because human life has inherent worth that no property law can override" (Stage 6) are both "steal it" answers — but they reveal entirely different moral architectures.
Two misconceptions are worth directly addressing. First: Kohlberg's stages are not about being a good or bad person. A Stage 2 reasoner and a Stage 5 reasoner can make the same choice; what differs is their understanding of why it is right. Second: postconventional reasoning is not the default outcome of aging. Kohlberg's longitudinal data showed that development stops for most people at the conventional level. Reaching postconventional reasoning requires both formal operational thinking (abstract, hypothetical reasoning about principles) and substantial experience confronting situations where rules and justice conflict — a combination that is cognitively demanding and not guaranteed by time alone. This is also why children cannot access postconventional reasoning: it requires the abstract thinking that only emerges in adolescence, and even then must be scaffolded by relevant experience.