1. Everyone is aware that there are degrees of seriousness in immorality. We have seen why not all immoral acts are equally serious (15‑A). We have also seen that the Church teaches not only that there are degrees of seriousness but that there is a sharp break between grave matter, required for mortal sin, and light matter (15‑B). This teaching articulates Christian understanding developed from divine revelation and in its light. The question to be answered here is why there is an absolute break between grave and light matter and so between fully deliberate venial sin and mortal sin.
2. A person who loves God ought by that very fact to love every human good, since every created good is a participation in divine goodness. One who loved every human good to the full extent of its goodness would proceed in perfect consistency with integral human fulfillment. But one who commits an immoral act is not acting in a manner consistent with integral human fulfillment. Therefore, it seems that every immoral act is at odds with the love of God.
3. Yet a venial sin is not incompatible with love of God. This is not difficult to understand if it is venial because of a lack of sufficient reflection or full consent, for the lack of either reduces or eliminates responsibility. However, one can also commit sins which are fully deliberate yet venial because of light matter—for example, cheating someone of a very small sum (see S.t., 1–2, q. 88, aa. 2, 5, 6).
Consider a man who would like a morning paper. Checking for change, he discovers that he lacks the coins necessary to purchase a paper from a vending box. However, he notices that the box is not latched tightly. The thought occurs: “I could take a paper without paying for it, but that would be wrong. However, the newspaper company will not be seriously hurt if I take a paper and close the box, so that subsequent customers will pay.” He hesitates momentarily, realizing the wrongness of the act, but is inclined to choose to do it anyway. A quick look about assures him there is no one to notice his pilferage. He filches the paper.
In a case like this, one might suppose that he did not reflect sufficiently and consent fully. However, the supposition of the example precisely is that he did. One also might suppose that he entertains some thoughts which could justify the act—for example, that he would pay double next time or that on some previous occasion the box has taken his coins without opening. But let us suppose he had no such thoughts.
Catholic moralists and the faithful in general would agree that, despite the sufficient reflection and full consent in this case, the act was not a mortal sin. What the man did is light matter.
4. A few theologians have held that of itself every kind of immorality would be grave matter, but God by a merciful fiat simply decrees that many sins people are likely to commit will not be mortal. This view is unsatisfactory, since it presupposes a legalistic conception of the relationship between moral action and one’s share in divine life. If God determines by fiat which immoralities remain mortal sins, there seems to be no intrinsic connection between living an upright life and remaining in his friendship. The requirement to avoid mortal sin becomes an arbitrary test.
5. This unsatisfactory position nevertheless does help clarify the essential point. The question is not why some moral evils constitute grave matter, but why some do not—why not all matter is grave. Charity is love of divine goodness; every evil is incompatible with divine goodness; even a small sin is a real evil; yet this real evil and love of God can coexist in one’s heart.1 How?
6. There is also a subordinate problem. Why is the division between grave and light matter made where it is and maintained so rigidly? Why, for instance, is the seeking of sexual orgasm apart from marital intercourse always grave matter, while many minor offenses against one’s neighbor—for example, slighting another—are only light matter?2
1. Assuming a certain theological view of venial sin, someone might object that venial sins are not opposed to God’s law but only beside it, not offenses against charity but only lacking in charity. The view of St. Thomas, along these lines, is criticized in question F. But the problem of light matter as it emerged in Catholic tradition involved the assumption that every venial sin is somehow opposed to God’s law, that even a venial sin requires a remedy and repentance, and that its remission (at least through temporal punishment after death) is required. See Eugene F. Durkin, The Theological Distinction of Sins in the Writings of St. Augustine (Mundelein, Ill.: Saint Mary of the Lake Seminary, 1952), 121–38, for a clear account of Augustine’s view of this matter.
2. Although one cannot agree entirely with the analysis, suggestive indications about the affinity between Lutheranism and theories of fundamental option which have emerged since 1960 in Catholic moral theology are provided by James F. McCue, “Simul iustus et peccator in Augustine, Aquinas, and Luther: Toward Putting the Debate in Context,” Journal of the American Academy of Religion, 48 (1980), 81–96.