  Among modern philosophers, it is again Rousseau (1979) who devotes the most attention to issues of development. He offers a sequence of five age-related stages through which a person must pass to reach moral maturity: (i) infancy (birth to age 2); (ii) the age of sensation (3 to 12); (iii) the age of ideas (13 to puberty); (iv) the age of sentiment (puberty to age 20); and (v) the age of marriage and social responsibility (age 21 on). Although he allows that an adult may effectively modify the behavior of children by explaining that bad actions are those that will bring punishment (90), he insists that genuinely moral reasoning will not be appreciated until the age of ideas, at 13 and older. In keeping with his stage theory of moral development he explicitly rejects Locke’s maxim, ‘Reason with children,’ (Locke, 1971) on the ground that attempting to reason with a child younger than thirteen years of age is developmentally inappropriate.