Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 88, a. 4, 5, 6; De Malo q. 2, a. 8; q. 7, a. 3 and 4.

**547. The conversion of mortal sin into venial, and vice versa, is not to be so understood as if the same sin in number of mortal sin which now in the concrete exists with all its circumstances could become venial; but that the act of sin which by genus, by its notion, in the abstract is mortal, can be only venially evil as in the concrete here and now it exists with its circumstances; and vice versa.

548. Mortal sin of itself or by genus can become venial, not indeed accidentally from a venially evil circumstance added to the act, because a light deformity added rather increases than diminishes sin; but:

a) If it is mortal from the whole genus, it becomes venial only from the disposition of the agent which subtracts something from the act: 1) from erroneous conscience which without grave negligence judges to be venial what is mortal; 2) from imperfect deliberation; and 3) from imperfect consent.

b) If it is mortal from its genus, it becomes venial from the three aforesaid ways, and moreover 4) from lightness of matter or on the part of the object, e.g. theft.

Venial sins from imperfect deliberation or imperfect consent are called venial from imperfection of the act: for they are imperfect human acts. According to S. Thomas imperfect deliberation and imperfect consent are possible in any matter.

549. Venial sin of itself becomes mortal, whether a) on the part of the agent because of a circumstantially or dispositionally mortal evil, — or b) on the part of the act because of a circumstance which changes the species and adds grave malice specifically distinct; — or c) from coalescence, multiplication or aggravation of matter. And indeed:

1°) from erroneous conscience which judges or doubts to be mortal what is only venial;

2°) by reason of the last end, when the sinner makes his last end in venial sin, i.e. when he is prepared to sin mortally because of that sin which of itself is venial, e.g. to omit Mass to play excessively or to steal something small;

3°) by reason of an adjoined end, as if one utters a slight lie or a slightly dishonest word to fornicate, or commits a slight theft for homicide;

4°) from formal and perfect contempt of the precept or of the prescriber, by which man violates the precept precisely because it is a precept, whatever it be whether grave or light, — or because the superior as superior prescribes, whatever he prescribes¹; 5°) by reason of grave scandal, as if you foresee that by a dishonest word you are to be an occasion of gravely sinning to another;

6°) by reason of the danger of neighbor falling into mortal sin, to which the sinner would expose himself without sufficient caution or necessity, e.g. conversation with a woman for a weak man: moreover, of what mortal sin he exposes himself to the danger is to be declared in confession;

7°) by reason of notable harm which from sin is foreseen to follow for neighbor, e.g. if a slight theft would place another in extreme necessity, or a quarrel would arise from too much loquacity;

8°) by reason of matter coalescing or multiplied, as is to be specially explained.

The seven former ways also hold for venial sin from its genus; the last only for venial sin from lightness of matter.

550. The rule for discerning whether venial sin from lightness of matter becomes mortal from aggravation and multiplication of matter is as follows: Several small matters can coalesce and are morally united into one grave, when they pertain to the same in number precept and to one transgression of the precept.

Thus minute thefts coalesce into one gravely unjust detention or damnification, likewise several small eatings, or omissions in the hours, on the same day taken together into one violation of the fast, or serious omission of the breviary; — on the contrary several small eatings or omissions on different days do not coalesce because they do not pertain to the same precept in number, nor do several light excesses in drink on the same day coalesce: since they do not consist in a permanent thing they do not pertain to one and the same transgression; they can however coalesce into one harm to health or family because in the notion of harm they are something permanent.

He who by several light transgressions arrives at grave matter, if he intended this from the beginning, commits one mortal sin; but if he did not intend it, he commits as many venial sins as there were light transgressions, the last excepted which is mortal because by it grave matter is completed: for by this act he wills the small matter inasmuch as it is united with others to compose grave matter.

Light transgressions following already completed grave matter, if they were intended from the beginning, constitute one mortal sin with the preceding ones but aggravate it externally; — but if they were not intended, they do not constitute a new mortal sin unless they pertain again to a new grave quantity: but if however they are considered as one thing with the preceding grave matter, they include mortal sin of joy or approval of it.