387. Those Subject to Law.--Only those are morally obliged to observe human law who are subjects of the lawgiver and who have the use of reason. (a) Those who are not subjects in any sense are not bound, for to obligate by law is an act of authority and jurisdiction; (b) those who have not reached the age of reason, or who are habitually insane, are not themselves morally bound, since they are incapable of moral obligation. Of course, they may be restrained as to acts, and their rights may be determined. 388. The lawgiver himself, even though not subject, is held to observe the laws he makes. Thus: (a) if the lawmaking power resides in a legislative assembly, each legislator is subject to the body and hence to its laws; (b) if the lawmaking power is vested in an individual, he is not subject to the coactive force of his own laws, since he cannot punish himself; but he is subject to their directive force, inasmuch as the higher law of nature requires that the superior show good example by observing what he requires of others. 389. Change of Law.--The growth of knowledge and experience, or the change of social circumstances, requires now and then that human laws be improved or adapted to new conditions. But, since laws derive a great part of their influence from custom, they should not be changed unless the break with custom is compensated for by the urgent necessity of the new law, by its manifest advantage, or by the evident iniquity or harmfulness of the old law, In brief, the common good should be the norm by which to decide whether a law should be retained or changed. 390. Constitutional law, as being fundamental and organic, is more immutable than ordinary law. (a) If given to a society established according to the positive ordinance of a superior, it cannot be abrogated or modified by the legislative authority of that society, since this would be contrary to the will of the founder. Hence, the Church has no power to change the fundamental constitution given her by Christ, who prescribed the religious society as established by Him to be necessary. (b) If a constitutional law is given to a society which is perfect and necessary from the law of nature, such constitution can be modified for extraordinary reasons and in the special ways provided (e.g., by amendments approved by the people). 391. The Law of Custom.--Custom (i.e., a long-continued practice that has acquired binding force) is able to establish a new law or to do away with an old law. For the will of the lawgiver is manifested not only by words, as happens in the written law, but also and more clearly by repeated and continued acts, as happens in the case of the unwritten law of custom. In a democracy it is the consent of the people who follow the custom as law that imposes the obligation; in a monarchy it is the consent of the ruler who permits the custom.