Piaget argued that the idea of morality is developed in certain stage of childhood, just like the understanding of the conservation of volume of water.

Kohlberg divided the development into pre-conventional, conventional, and post-conventional stages. He noticed that conventional rules and moral rules are treated differently.

Turiel developed method to tell apart conventions from moral rules: unalterable, universal. He suggested that the morality is attained on the basis of fairness and harm.

Shweder found that the line between convention and morality differs according to the culture.(Jonathan Haidt, 2012)

In korea, the courtesy is part of the morality.