The true efficient cause of an ecclesiastical
custom, in as far as it constitutes law, is solely the consent of the competent legislating authority. All church laws imply spiritual jurisdiction, which resides in the hierarchy alone, and, consequently, the faithful have no legislative power, either by
divine right or canonical statute. Therefore, the express or tacit consent of the church authority is necessary to give a custom the force of an ecclesiastical law. This consent is denominated legal when, by general statute and antecedently, reasonable customs receive approbation. Ecclesiastical custom differs, therefore, radically from civil custom. For, though both arise from a certain conspiration and accord between the people and the lawgivers, yet in the Church the entire juridical force of the custom is to be obtained from the consent of the hierarchy while in the civil state, the people themselves are one of the real sources of the legal force of custom. Custom, as a fact, must proceed from the community, or at least from the action of the greater number constituting the community. These actions must be free, uniform, frequent, and public, and performed with the intention of imposing an obligation. The usage, of which there is question. must also be of a reasonable nature. Custom either introduces a new law or abrogates an old one. But a law, by its very concept, is an ordination of reason, and so no law can be constituted by an unreasonable custom. Moreover, as an existing statute cannot be revoked except for just cause, it follows that the custom which is to abrogate the old law must be reasonable, for otherwise the requisite justice would be wanting. A custom, considered as a fact, is unreasonable when it is contrary to divine law, positive or natural; or when it is prohibited by proper ecclesiastical authority; or when it is the occasion of sin and opposed to the common good. A custom must also have a legitimate prescription. Such prescription is obtained by a continuance of the act in question during a certain length of time. No canonical statute has positively defined what this length of time is, and so its determination is left to the wisdom of canonists. Authors generally hold that for the legalizing of a custom in accordance with or beside the law a space of ten years is sufficient; while for a custom contrary to law many demand a lapse of forty years. The reason given for the necessity of so long a space as forty years is that the community will only slowly persuade itself of the opportuneness of abrogating the old and embracing the new law. The opinion, however, which holds that ten years suffices to establish a custom even contrary to the law may be safely followed. In practice the
Roman Congregations scarcely tolerate or permit any custom, even an immemorial one, contrary to the sacred canons. In the introduction of a law by prescription, it is assumed that the custom was introduced in good faith, or at least through ignorance of the opposite law. If, however, a custom be introduced through connivance, good faith is not required, for, as a matter of fact, bad faith must, at least in the beginning, be presupposed. As, however, when there is question of connivance, the proper legislator must know of the formation of the custom and yet does not oppose it when he could easily do so, the contrary law is then supposed to be abrogated directly by the tacit revocation of the legislator. A custom which is contrary to good morals or to the natural or divine
positive law is always to be rejected as an abuse, and it can never be legalized. ==Force of custom==