THIRD ARTICLE [I-II, Q. 97, Art. 3]

Whether Custom Can Obtain Force of Law?

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 (Q. 93, A. 3; Q. 95, A. 2).  But human custom cannot change either the law of nature or the Divine law.  Therefore neither can it change human law.

Obj. 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.

Obj. 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 Obj. 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.”