1. It is clear from the preceding that a mortal sin is a sin which is incompatible with divine life. Those who commit and remain in mortal sin are excluded from the kingdom of God; they are separated from Jesus; they evict the Holy Spirit from their hearts. They incapacitate themselves for life in the Church, particularly for the reception of Holy Communion, which expresses and nourishes the living unity of humankind redeemed in Jesus.
2. The conditions required for mortal sin are three: grave matter, sufficient reflection, and full consent (see S.t., 1–2, q. 88, aa. 2–6). Explained briefly here, these conditions will be examined in greater detail in the next two chapters.4
3. It is common theological teaching that certain kinds of acts are of themselves light matter—for example, idle talk, lack of diligence in prayer, and so on. Other kinds of acts are of themselves grave matter—killing the innocent, adultery, lying, theft, and so on. Of the latter, however, some necessarily bring about great harm: In killing the innocent the victim cannot be only somewhat dead, and in adultery the marriage bond cannot be only slightly defiled. Others can sometimes involve slight harm: In stealing, one can take a newspaper without paying for it or one can take somebody’s entire livelihood; in lying, one can make a harmless joke or one can practice deception in a matter of life and death.
4. Acts of kinds which admit of smallness in the harm done (parvity of matter) are not necessarily grave. They will not be matter for mortal sin if the parvity of matter makes a particular instance so light that it simply cannot count as an act of that kind. For example, to sample one grape as one passes by a vineyard is too slight a matter to count as theft.5
For practical purposes, Catholics must consider grave matter what the Church teaches is such, since they ought to conform their consciences to the Church’s teaching. When the precise teaching of the Church is not clear, two points should be borne in mind.
First, when the Church teaches that a certain kind of act always is wrong, then any more specific kind of act which includes all the characteristics of that general sort of act also is always wrong. For example, since the Church teaches clearly that any positive act intended to impede procreation from following upon marital intercourse always is gravely wrong, the more specific act of impeding procreation by anovulant drugs in order to limit the size of the family to a reasonable number also is always gravely wrong. Similarly, since the Church teaches clearly that any act intended to kill the innocent always is wrong, the more specific act of intending to kill millions of innocent persons by a retaliatory strike in case of nuclear war also is always gravely wrong.
Second, when the Church’s teaching is not clear—for example, when there is disagreement even among the classical theologians—that something is grave matter, then no one, except a bishop or pope, on his or her own judgment ought to tell anyone else that the matter is grave. For example, a priest who is convinced that his parishoners ought not to vote for a candidate who favors euthanasia nevertheless should not tell his congregation that such a vote would be a mortal sin. Again, although failure to do works of mercy can be mortally sinful, the obligation in any particular instance is not easy to determine; therefore, someone urging contributions to a special collection to alleviate starvation should not say failure to contribute is grave matter.
5. For a sin to be mortal, it is enough that a person who is willing to sin believe the matter to be grave. One willing to violate conscience in what he or she thinks a grave matter is guilty of the degree of moral evil willingly accepted. Similarly, a person who suspects that the matter might be grave and acts without taking reasonable care to eliminate doubt is guilty of the grave moral evil he or she suspects.
6. Sufficient reflection requires more than just awareness of what one is doing. Without this there is no human act at all. Sufficient reflection also requires awareness that the act is gravely wrong. In other words, reflection sufficient for mortal sin exists only if two conditions are met: (1) one acts in violation of one’s conscience, and (2) one’s conscience is that the matter either is grave or might be grave.
7. At the relevant time, one must actually be aware of the act’s wrongness. It is not sufficient simply that one could and should be aware, for in such a case one is primarily responsible for the failure to form conscience but is not gravely responsible for each unrecognized evil consequent upon this failure.
8. The relevant time is the time of decision, not of execution. For example, realizing that he or she has a grave obligation to seek help and foreseeing future neglect of family responsibilities otherwise, an alcoholic nevertheless decides now not to seek help. The relevant time is the time when this decision is made. The decision is made with sufficient reflection, although the neglect consequent on the choice will occur later, when the alcoholic is no longer able to think or care about family responsibilities.
9. Reflection can be insufficient when one’s state of consciousness is such that one does not attend clearly to what one is about to do: in cases of extreme fatigue, semiwakefulness, partial sedation, great pressure, distraction, and so on. In such circumstances it can be a sign of insufficient reflection that the individual in no way planned the act in that situation, that the act was out of character, and that it was firmly rejected as soon as it was considered with full attention.
10. It is not necessary for sufficient reflection that one think specifically of what the act’s wrongness consists in. For example, a candidate for public office might realize that there was something seriously questionable about accepting a certain campaign contribution, without knowing exactly how it would be corrupt to take it.
11. Similarly, it is not necessary for sufficient reflection that one think explicitly that the act is an offense against God or will damage one’s relationship with him. At the same time, no well-instructed Catholic is likely to recognize an act as seriously wrong without having some awareness of this most important implication of sin. If this awareness is really lacking in such a person, it is a sign that the act’s wrongness was probably not clear enough for sufficient reflection to have taken place.
12. Full consent is a definite choice. Even when aware that an act would be gravely evil, one has not sinned until one has made a definite choice. The choice itself need not bear only upon a wrongful performance, but can carry out an immoral commitment, can bear instead upon an omission, or can involve (without bearing upon) the acceptance of consequences one is gravely obliged to avoid.
13. One can make a choice without expressing it in words or carrying it out in any sort of behavior. One can also make a choice which leaves open a range of possibilities to be settled by additional choices. For example, a person can decide to indulge in some form of illicit gratification and only then deliberate about specifics. In such cases, the choice required for a mortal sin is made as soon as a proposal involving grave matter, however generally understood, is accepted with sufficient reflection.
14. Judgments of conscience can bear upon the process of deliberation itself as well as upon other acts. If an individual is sufficiently aware of a grave obligation to deliberate and decide a certain matter yet chooses not to do so, or is sufficiently aware of a grave obligation to set aside a certain deliberation (for instance, by directing attention to something else) yet chooses to persist in it, then an actual choice which is mortally sinful has been made.
A member of a community, aware that another is doing something seriously wrong, can be aware of an obligation to deliberate about possible ways of remedying the situation. Although this obligation might be recognized as grave, the possible unpleasantness of fulfilling it could lead to a temptation to set the problem aside. Such a choice, inconsistent with a judgment of conscience recognizing the seriousness of the obligation to deliberate, would be a mortal sin.
15. If a mortally sinful choice is not repented, subsequent voluntary acts and omissions in grave matter, supposing them to be sufficiently known as such, can continue the initial sin and, as it were, unfold its implications in new circumstances. This can occur by executive willing, even without further, distinct choices in each new instance of sin.
4. The practical implications of what is said here and in the remainder of this question, if not evident from reflection or established from other sources, have the weight of the consensus of the classical theologians. To the extent that this consensus was accepted by bishops as a norm in the formation of confessors, it remains a safe guide for pastoral practice. See Arthurus Vermeersch, S.J., Theologiae Moralis: Principia, Responsa, Consilia, tomus 1, Theologia Fundamentalis (Rome: Apud Aedes Universitatis Gregorianae, 1947), sections 381–402; I. Aertnys and C. Damen, C.Ss.R., Theologia Moralis secundum Doctrinam S. Alphonsi de Ligorio, ed. J. Visser, C.Ss.R., ed. 17, vol. 1 (Rome: Marietti, 1956), sections 233–38; Benedictus Henricus Merkelbach, O.P., Summa Theologiae Moralis ad Mentem D. Thomae, vol. 1, De Principiis (Paris: Desclée de Brouwer, 1942), sections 538–50.
5. The conception of acts in themselves grave in kind but falling short of gravity due to parvity of matter is in St. Thomas, De malo, q. 10, a. 2; cf. q. 12, a. 3; q. 13, a. 2. St. Thomas does not admit parvity of matter in sexual sins except for those incidental to marital intercourse open to procreation: q. 15, a. 2, c. and ad 18. Many theologians categorize venial sins otherwise than indicated here, the most common alternative being to consider sins venial by parvity of matter to constitute a category in themselves, rather than to reduce such sins to objective imperfection of the act, as is done here following St. Thomas. See Marcelino Sánchez, O.P., “Las Categorias del Pecado Venial,” Studium Revista de Filosofia y Teologia, 12 (1972), 319–32.