This is a translated text excerpted from Lawrence Kohlberg's (1927-1987) book  The Psychology of Moral Development: The Nature and Validity of Moral Stages.  In this text Kohlberg explains his cognitive-developmental theory of moralization. He defends the hypothesis advanced by the Swiss psychologist Jean Piaget (1896-1980). Stated in broad outline, the Piaget hypothesis says that the child goes through stages or moral development. According to the research undertaken by Kohlberg, these are real moral stages which can be see observed and proved in terms of six basic stages – not two as Piaget suggested—which can be grouped into three levels,  each of which has two stages. Every level represents a "form" of moral reasoning, where the second stage is a more advanced and better organized form of the main idea of each level. Kohlberg claims that his stages form a universal invariant sequence ,  and there is a parallelism between the stages of moral and logical development. Logical development is a necessary but not a sufficient  condition  for moral development.