How to understand Piaget's theory of stages of moral development?

Piaget's Stages of Moral Development Theory is a psychological theory of the development of human moral cognition and behavior that proposes three stages of human moral development. This theory is widely recognized as one of the key theories in the field of moral developmental psychology.

Piaget's Stages of Moral Development Theory suggests that human moral development is a gradual process, and that people will have different moral cognition and behavioral performance at different ages. Specifically, Piaget divided human moral development into three stages:

Pre-traditional stage: in this stage, people's moral cognition is mainly based on the principle of external punishment and reward, i.e., people will abide by the rules and moral norms because they are afraid of being punished or hope to be rewarded.

Traditional Stage: In this stage, people's moral cognition is primarily based on the principle of social norms and moral codes, i.e., people will follow rules and moral codes because they believe that these rules and codes are the cornerstone of society and should be followed.

Post-Traditional Stage: In this stage, people's moral cognition is primarily based on the principle of their own moral principles and values, i.e., people will follow the rules and moral codes because they consider themselves to be right and in line with their own values and principles.