Each citizen of a state promises, in the original compact, that he will promote, as far as lies in his power, all the conditions of the possibility of the state; hence, also, the condition just mentioned. This he can best do by educating children who may grow up to realize various ends of reason. The state has the right to make this education of children a condition of the state-compact, and thus education becomes an external, legal obligation, which the parents owe to the state.