Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 97, a. 3.

404. Custom, considered as a fact, properly is use or manner, i.e. the frequent repetition of the same acts, a frequent manner of acting and the inclination thence arising to act similarly. In the present however, in juridical speech, it designates law introduced by the use or manners of a people¹. Which is usually defined as : statute law, introduced by the long-standing customs of the community with some consent of the legislator.

But custom is either according to law (adhesive or declaratory) which interprets a law previously enacted, or against law which abrogates the law or derogates from it, or beyond law which introduces a new law, as is that which is already confirmed by can. 135.

The conditions required for custom are :

a) On the part of the acts that they be 1° frequent, i.e. often repeated ; 2° of long standing, i.e. exercised for a long time ; 3° uniform or constant and therefore not interrupted, either on the part of the people, or on the part of a contradicting superior ; 4° public and known, otherwise there would not be a custom of the society as such ; 5° deliberate or freely placed, and not placed by force or fear or error by which the consent of the community is impeded ; 6° frequented not by a few particular persons, but by the greater part of the community, or of the part for which a law can be enacted (can. 26), as for example of the diocese, of a class of faithful, of a religious order or of a province of it, but not of a parish or of a religious house.

b) On the part of matter, that the custom be reasonable (can. 27) at least negatively, and therefore that the conditions necessary for a law be present.

c) On the part of the subjects, the intention of obliging themselves, (or of disobligating themselves, or of understanding and fulfilling the obligation in such a way, or of extending or limiting the obligation to this), which can be manifested by the word or deed of the superior or of the subjects, by practice, by the common judgment of experts, etc. : thus customs out of gratitude or devotion, as for example of hearing three Masses on the feasts of God, of signing oneself with holy water, of saying « The Angel of the Lord... », are not obligatory.

d) On the part of the legislator, consent (can. 25) either special, expressed or tacit, which is gathered from action or omission, or general or presumed given to every legitimate custom, that of approving whatever customs adorned with certain conditions.

405. What Law establishes about custom. — According to the new Law ;

1° For the introduction of custom beyond law now 40 continuous and complete years are required (can. 28) ; when the required time is present, the custom is called prescribed (can. 27).

Custom however differs from prescription :

a) the latter is the way by which private persons acquire a right, the former induces an effect for the community ;

b) for prescription good faith is required by which one does not know that the thing is not his own ; for custom it is not always required that those introducing it be ignorant that the law exists ;

c) for prescription the consent of him against whom prescription is made is not required ; for custom the consent of the legislator is required ;

d) for prescription and custom a different continuous time is required : for prescription ordinarily 30 years suffice, or another less time determined by law ; for custom, 40 years.

2° Custom against law or beyond law is revoked by contrary custom or law (can. 30).

3° However, unless it expressly mentions them, a law does not revoke a centenary or immemorial custom, just as neither does a general law revoke particular customs (can. 30).

Whence, by the promulgation of the New Code, centenary and immemorial customs are not removed, unless expressly reprobated there (can. 5).

406. How custom obtains the force of law. — Custom, furnished with the due conditions, just as it can enact laws, so it can also abrogate them and derogate from them. Which is done in a twofold way :

a) By the way of connivance or by special personal consent, the superior personally knowing and consenting either expressly or tacitly, i.e. not contradicting when he can and should conveniently contradict : for he is not considered to consent if the custom is irrational, as for example if it is contrary to divine right, gives occasion for sinning, is harmful to the common good, dangerous to the faith, pernicious to ecclesiastical discipline, to divine worship, to the liberty of the Church, or in law is expressly reprobated as an abuse or corruption (can. 27, § 2), such as is custom contrary to the preceptive rubrics of the Mass (can. 818) ; unless it be so said because of circumstances now changed. This of itself does not require time but holds as soon as it is evident that consent is present : thus a law which was never received by use, ceases to oblige after a few acts tolerated by the superior.

b) By the way of prescription or by consent not special but general, not personal but legal or juridical (which is contained in a law that ratifies all legitimate customs), the superior even being ignorant of the custom and giving presumed consent : this requires that it be reasonable and continued for a long time, nor interrupted ; otherwise it does not sufficiently appear that the law is not accommodated to the customs of the subjects nor could the legislator be presumed to consent. How much time is required, is to be determined by the judgment of the prudent.

Now however it is universally established in law that no custom can derogate from an ecclesiastical law unless it has been legitimately prescribed for 40 continuous and complete years ; but from a law which contains a clause prohibiting future customs, only a centenary or immemorial custom can prescribe (can. 27, § 1).

Wherefore to some it has seemed that a custom tacitly approved by the way of connivance is no longer valid, unless it has also lasted 40 years (or 100) without interruption. But they do not show this efficaciously.

407. How custom against law can be introduced. — To understand how a custom against law can be introduced, even without sin, let S. Thomas be heard, q. 97, a. 3, ad 2 : « Human laws in some cases fail. Whence it is possible sometimes to act beyond the law, namely in a case in which the law fails (epikeia), and then the act will not be evil ; and when such cases are multiplied because of some change in men, then it is manifested by custom that the law is no longer useful ; just as it would also be manifested if a contrary law were promulgated by word. If however the same reason still remains, for which the first law was useful, custom does not prevail against the law, but the law against custom ; unless perhaps the law seems useless only because of this, that it is not possible according to the custom of the country, which was one of the conditions of the law. For it is difficult to remove the custom of a multitude ».

From this latter it is already understood that it is not necessary that every custom against law be introduced legitimately and without sin ; as moderns are wont to note with S. Alphonsus, Th. M., l. I, n. 107 : « Custom against law does not require good faith, but it can also be introduced by sinning. For custom has a threefold state. In the beginning those introducing [it] against the law all sin (unless they are excused by some reason). In the progress those using [it] already introduced by the greater number (in good faith) do not sin, but they can be punished by the prince. In the end however those using [it] already prescribed neither sin nor can be punished ».

408. Custom can do all that the legislator [can do], as for example abrogate the obligation in conscience as to fault and not as to penalty, or vice versa ; likewise abrogate irritant laws ; indeed even laws which are enacted with the clause : notwithstanding any custom to the contrary, because this regards customs already existing, but does not impede future ones. But it cannot change the law against the legislator when he wishes it not to be changed by custom, as if he contradicts it ; whence if a law was enacted with the clause : notwithstanding any custom even future, the law does not presume consent unless the custom is centenary or immemorial (can. 27).

409. Custom ceases 1) intrinsically, if it becomes irrational,

2. extrinsically, by a contrary custom legitimately prescribed,

3. likewise by a law which suppresses it. However :

a) Special laws of places, as particular customs, statutes and privileges, because they are reasonable, yet easily able to be unknown by the universal legislator, are not considered to be abrogated by a contrary universal law, even if it is enacted with the clause : notwithstanding custom ; unless the law specially and expressly indicates it as for example by saying : none withstanding, or notwithstanding any contrary custom (can. 30) ; they are however removed by a law enacted by the particular legislator of the place.

b) Likewise an immemorial or centenary custom is not considered to be abrogated even by a law which is enacted notwithstanding any custom, unless it expressly indicates it, as for example by adding « even centenary », or implicitly, by declaring it « irrational or a corruption » (can. 30).