Piaget

Piaget² has conducted many careful studies on the evolution of games during childhood, and has suggested that moral behavior consists in a system of rules, and the essence of all morality is to be sought for in the respect which the individual acquires for these rules.³ Piaget thus equates morality, or ethical feeling and conduct, with the individual's attitude toward and practice of various rules. This perspective provides a rational basis for the analysis of moral schemes as games, and of moral behavior as the players’ actual conduct.

1974, Thomas S. Szasz, chapter 12, in The Myth of Mental Illness, →ISBN, page 201