Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that custom cannot obtain force of law, nor abolish a law. Because human law is derived from the natural law and from the Divine law, as stated above (Question 93, Article 3; Question 95, Article 2). But human custom cannot change either the law of nature or the Divine law. Therefore neither can it change human law.

Objection 2: Further, many evils cannot make one good. But he who first acted against the law, did evil. Therefore by multiplying such acts, nothing good is the result. Now a law is something good; since it is a rule of human acts. Therefore law is not abolished by custom, so that the mere custom should obtain force of law.

Objection 3: Further, the framing of laws belongs to those public men whose business it is to govern the community; wherefore private individuals cannot make laws. But custom grows by the acts of private individuals. Therefore custom cannot obtain force of law, so as to abolish the law.

On the contrary, Augustine says (Ep. ad Casulan. xxxvi): "The customs of God's people and the institutions of our ancestors are to be considered as laws. And those who throw contempt on the customs of the Church ought to be punished as those who disobey the law of God."

I answer that, All law proceeds from the reason and will of the lawgiver; the Divine and natural laws from the reasonable will of God; the human law from the will of man, regulated by reason. Now just as human reason and will, in practical matters, may be made manifest by speech, so may they be made known by deeds: since seemingly a man chooses as good that which he carries into execution. But it is evident that by human speech, law can be both changed and expounded, in so far as it manifests the interior movement and thought of human reason. Wherefore by actions also, especially if they be repeated, so as to make a custom, law can be changed and expounded; and also something can be established which obtains force of law, in so far as by repeated external actions, the inward movement of the will, and concepts of reason are most effectually declared; for when a thing is done again and again, it seems to proceed from a deliberate judgment of reason. Accordingly, custom has the force of a law, abolishes law, and is the interpreter of law.

Reply to Objection 1: The natural and Divine laws proceed from the Divine will, as stated above. Wherefore they cannot be changed by a custom proceeding from the will of man, but only by Divine authority. Hence it is that no custom can prevail over the Divine or natural laws: for Isidore says (Synon. ii, 16): "Let custom yield to authority: evil customs should be eradicated by law and reason."

Reply to Objection 2: As stated above (Question 96, Article 6), human laws fail in some cases: wherefore it is possible sometimes to act beside the law; namely, in a case where the law fails; yet the act will not be evil. And when such cases are multiplied, by reason of some change in man, then custom shows that the law is no longer useful: just as it might be declared by the verbal promulgation of a law to the contrary. If, however, the same reason remains, for which the law was useful hitherto, then it is not the custom that prevails against the law, but the law that overcomes the custom: unless perhaps the sole reason for the law seeming useless, be that it is not "possible according to the custom of the country" , which has been stated to be one of the conditions of law. For it is not easy to set aside the custom of a whole people.

Reply to Objection 3: The people among whom a custom is introduced may be of two conditions. For if they are free, and able to make their own laws, the consent of the whole people expressed by a custom counts far more in favor of a particular observance, that does the authority of the sovereign, who has not the power to frame laws, except as representing the people. Wherefore although each individual cannot make laws, yet the whole people can. If however the people have not the free power to make their own laws, or to abolish a law made by a higher authority; nevertheless with such a people a prevailing custom obtains force of law, in so far as it is tolerated by those to whom it belongs to make laws for that people: because by the very fact that they tolerate it they seem to approve of that which is introduced by custom.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod consuetudo non possit obtinere vim legis, nec legem amovere. Lex enim humana derivatur a lege naturae et a lege divina, ut ex supradictis patet.

Sed consuetudo hominum non potest immutare legem naturae, nec legem divinam. Ergo etiam nec legem humanam immutare potest.

Argumentum 2

Praeterea, ex multis malis non potest fieri unum bonum. Sed ille qui incipit primo contra legem agere, male facit. Ergo, multiplicatis similibus actibus, non efficietur aliquod bonum.

Lex autem est quoddam bonum, cum sit regula humanorum actuum.

Ergo per consuetudinem non potest removeri lex, ut ipsa consuetudo vim legis obtineat.

Argumentum 3

Praeterea, ferre legem pertinet ad publicas personas, ad quas pertinet regere communitatem, unde privatae personae legem facere non possunt. Sed consuetudo invalescit per actus privatarum personarum. Ergo consuetudo non potest obtinere vim legis, per quam lex removeatur.

Sed Contra

Sed contra est quod Augustinus dicit, in Epist. Ad casulan., mos populi dei et instituta maiorum pro lege sunt tenenda.

Et sicut praevaricatores legum divinarum, ita et contemptores consuetudinum ecclesiasticarum coercendi sunt.

Corpus

Respondeo dicendum quod omnis lex proficiscitur a ratione et voluntate legislatoris, lex quidem divina et naturalis a rationabili dei voluntate; lex autem humana a voluntate hominis ratione regulata. Sicut autem ratio et voluntas hominis manifestantur verbo in rebus agendis, ita etiam manifestantur facto, hoc enim unusquisque eligere videtur ut bonum, quod opere implet. Manifestum est autem quod verbo humano potest et mutari lex, et etiam exponi, inquantum manifestat interiorem motum et conceptum rationis humanae. Unde etiam et per actus, maxime multiplicatos, qui consuetudinem efficiunt, mutari potest lex, et exponi, et etiam aliquid causari quod legis virtutem obtineat, inquantum scilicet per exteriores actus multiplicatos interior voluntatis motus, et rationis conceptus, efficacissime declaratur; cum enim aliquid multoties fit, videtur ex deliberato rationis iudicio provenire. Et secundum hoc, consuetudo et habet vim legis, et legem abolet, et est legum interpretatrix.

Ad 1

Ad primum ergo dicendum quod lex naturalis et divina procedit a voluntate divina, ut dictum est.

Unde non potest mutari per consuetudinem procedentem a voluntate hominis, sed solum per auctoritatem divinam mutari posset. Et inde est quod nulla consuetudo vim obtinere potest contra legem divinam vel legem naturalem, dicit enim Isidorus, in synonym., usus auctoritati cedat, pravum usum lex et ratio vincat.

Ad 2

Ad secundum dicendum quod, sicut supra dictum est, leges humanae in aliquibus casibus deficiunt, unde possibile est quandoque praeter legem agere, in casu scilicet in quo deficit lex, et tamen actus non erit malus. Et cum tales casus multiplicantur, propter aliquam mutationem hominum, tunc manifestatur per consuetudinem quod lex ulterius utilis non est, sicut etiam manifestaretur si lex contraria verbo promulgaretur. Si autem adhuc maneat ratio eadem propter quam prima lex utilis erat, non consuetudo legem, sed lex consuetudinem vincit, nisi forte propter hoc solum inutilis lex videatur, quia non est possibilis secundum consuetudinem patriae, quae erat una de conditionibus legis. Difficile enim est consuetudinem multitudinis removere.

Ad 3

Ad tertium dicendum quod multitudo in qua consuetudo introducitur duplicis conditionis esse potest. Si enim sit libera multitudo, quae possit sibi legem facere, plus est consensus totius multitudinis ad aliquid observandum, quem consuetudo manifestat, quam auctoritas principis, qui non habet potestatem condendi legem, nisi inquantum gerit personam multitudinis. Unde licet singulae personae non possint condere legem, tamen totus populus legem condere potest. Si vero multitudo non habeat liberam potestatem condendi sibi legem, vel legem a superiori potestate positam removendi; tamen ipsa consuetudo in tali multitudine praevalens obtinet vim legis, inquantum per eos toleratur ad quos pertinet multitudini legem imponere, ex hoc enim ipso videntur approbare quod consuetudo induxit.