Summa Theologiae Moralis, vol. I: De Principiis

On the Quantity or Gravity of Obligation.

S. Th. II-II, q. 105, a. 2.

341. The gravity of obligation in ecclesiastical law depends on two things : on the gravity of the matter and on the will of the legislator, who at least must have the implicit intention of obliging under grave [matter]. Whence

a) if the matter is in every respect, even in end and circumstances considered, light, the law cannot oblige under grave [matter] : for such matter is not capable of grave obligation, nor can the legislator make it so that light matter which contributes little and influences lightly the end or common good, contribute much and influence gravely, or that small disobedience be great ; otherwise such a law is not conformed to reason, nor would it tend to the common good, but rather would be an occasion of ruin ;

b) if the matter is grave and the legislator intends to oblige under light, the obligation is only light : for in distinction from natural law, in which the obligation and its gravity necessarily and immediately arise from the very gravity and necessity of the matter, the proximate and immediate cause of obligation in positive law is the will of the legislator ; so great therefore is the obligation as the legislator wills, and just as it depends on him whether the law exists and obliges, so whether it is grave or light. And although by so acting the legislator can sometimes sin, the obligation however, because it is the effect of his will, does not extend beyond what he has willed.

342. The gravity of matter is estimated by reason of the end and of the aptitude for this end :

A. Matter is indeed grave, when it is an efficacious means for a great good, namely when the special or proximate end is of great moment as to the common good, very useful, morally necessary, and at the same time that which is prescribed by the law greatly contributes to obtaining the end. Such is the dignity of sacred worship, the service of God, penance, the sanctity of the clergy, etc. to which the use of sacred vestments, the observance of feasts, abstinence from meat, celibacy greatly contribute. Whence a thing in itself light can be grave matter, as was the eating of the forbidden fruit in paradise by reason of the acknowledgment of God and of the subjection of man to God : so e.g. entering a house by reason of scandal or danger, mixing water and wine by reason of the representation of the great mystery in the sacrifice.

B. On the contrary, if the special end is not of great moment, or if it is of great moment and the action does not greatly contribute to the end, the matter is light ; thus to the glorification of God the order between the various hours of the breviary does not greatly contribute.

343. Practical rules for discerning grave or light obligation.

A. Positive law obliges under grave [matter], when the matter is grave, i.e. greatly contributes to an end of great moment, and at the same time the legislator wishes to prescribe under grave [matter].

B. But the legislator wishes to oblige under grave [matter]

a) if he uses gravely threatening or more severe words, e.g. if he commands in virtue of holy obedience, under the indignation of God, under the threat of the divine judgment, etc.

b) if he imposes a grave penalty, e.g. of death, mutilation, perpetual prison, exile, deposition, privation of honors, censure, irregularity, reservation, privation of ecclesiastical burial (can. 2218 § 2) ; for the penalty, in order to be just, must be proportioned to the offense ;

c) if in grave matter he uses ordinary words : we command, we prescribe, we forbid, etc. and does not express that he wishes to oblige under light, nor is this gathered from the circumstances, especially e.g. from the excessive burden which the law would impose, he is considered to oblige under grave [matter] : for he is reasonably presumed to act reasonably and ordinarily to oblige according to the capacity and exigence of the matter. Nor must he explicitly intend grave obligation : just as he must not explicitly intend obligation in conscience but make a law, and so implicitly wills the obligation, in the same way by prescribing grave matter, he is considered implicitly to wish to prescribe under grave [matter] ;

d) if the custom and usage of the faithful and the practice of the God-fearing so interpret the law ;

e) if the prudent, pious and learned so unanimously judge.

C. If there is doubt about these, the law is considered to oblige under light, unless the legislator urges it under grave [matter], because then the presumption stands for him.