Essays on Moral Development (2 vols.)

The unifying claim is that moral development proceeds through a universal, invariant sequence of six stages, each representing a more differentiated and adequate structure of justice reasoning. Volume 1 establishes the philosophical foundation: the stages are not culturally relative values but increasingly adequate conceptions of fairness, rights, and obligation. Volume 2 provides the psychological evidence: longitudinal studies demonstrating that individuals move through the stages in order without skipping, and that the sequence holds across cultures. Kohlberg treats moral development as simultaneously a philosophical and empirical project, resisting the fact-value divide.

Kohlberg himself addresses this in the preface: each volume stands independently, but the flow of ideas logically suggests reading Volume 1 before Volume 2 . Volume 1, The Philosophy of Moral Development, lays out the moral and political philosophy underlying the stages, engaging Plato, Dewey, and Rawls. Volume 2, The Psychology of Moral Development, presents the empirical research program—longitudinal data, cross-cultural studies, the relationship of judgment to action—and includes Kohlberg's detailed replies to critics, co-authored with Charles Levine and Alexandra Hewer . Readers seeking the philosophical case should start with Volume 1; those interested in the evidence and the defense should prioritize Volume 2.

Kohlberg refined the stage model by clarifying that stages describe formal properties of justice reasoning, not the content of moral beliefs. He distinguished 'hard' structural stages from 'soft' developmental trends and revised the substage system. In Volume 2, he and his collaborators presented the 'current formulation' of the theory alongside synopses of specific criticisms from Gilligan, Gibbs, and others . The earlier essays had introduced the six stages; these volumes defend and revise them, acknowledging ambiguities about Stage 6 and clarifying that moral judgment is necessary but not sufficient for moral action.

Kohlberg argues that Gilligan's charge of gender bias misconstrues the theory's object. The stages describe how a person reasons about justice—fairness, rights, and obligations—not what specific values they hold. He contends that women and men do not differ in their capacity for justice reasoning, attributing observed score differences to educational and occupational opportunities rather than inherent deficiency. The reply, presented with Levine and Hewer in Volume 2, acknowledges Gilligan's care orientation as a legitimate moral domain but insists it operates alongside, not instead of, justice reasoning. Critics continue to debate whether this defense adequately addresses the theory's cultural and gendered assumptions.

Kohlberg's framework has been applied in moral education programs, particularly 'just community' schools that engage students in democratic governance and peer moral discussion. His hypothetical dilemmas and scoring systems have been used in research on professional ethics, including medical and legal education. Developmental psychology and moral philosophy continue to engage his stage model as a benchmark, even when rejecting its strong claims. The volumes' integration of philosophical and psychological inquiry has influenced how researchers conceptualize the relationship between moral reasoning and moral behavior, particularly through the judgment-action gap identified in his work with Daniel Candee.

The core claim of a universal, invariant sequence has been partially supported but substantially qualified. Longitudinal studies confirm that moral reasoning develops in a rough developmental order, but stage transitions are less uniform than Kohlberg claimed, and Stage 6 is rarely observed empirically. Cultural psychology has challenged the assumption that justice reasoning is the sole measure of moral maturity, documenting care, community, and divinity-based moral concerns that Kohlberg's scheme underweights. The 2024 Kohlberg Memorial Lecture argued that moral maturity requires humane regard—respect for agency combined with concern for suffering—which exceeds Kantian justice alone. Kohlberg's volumes remain foundational, but as a starting point for debate rather than a settled science.