All the principles I have hitherto attempted to establish, presuppose men to have the full use of their mature powers of understanding. For they are all grounded on the conviction, that the man who thinks and acts for himself should never be robbed of the power of voluntarily deciding on all that concerns himself, according to the results of his deliberations. Hence, then, they cannot be applied to persons such as lunatics and idiots, who are almost wholly deprived of reason, or to those in whom it has not reached that maturity which depends on the maturity of the body. For, however indefinite and, strictly speaking, incorrect, the latter standard may be, still there can be no other generally valid test to enable us to judge. Now, all these need, in the strictest sense, a positive care for their physical and moral well-being, and the merely negative preservation of their security is not enough in their case. But, to begin with children, who constitute the largest and most important class of such persons, it is evident that the care for their welfare, in virtue of the principles of justice, belongs to certain persons, that is, their parents. It is their duty to bring up their offspring to full maturity; and from this duty, and as a necessary condition of fulfilling it, arise all their rights with regard to them.