I answer that, Venial and mortal differ as perfect and imperfect in the genus of sin, as stated above (A. 1, ad 1).  Now the imperfect can become perfect, by some sort of addition:  and, consequently, a venial sin can become mortal, by the addition of some deformity pertaining to the genus of mortal sin, as when a man utters an idle word for the purpose of fornication.  On the other hand, the perfect cannot become imperfect, by addition; and so a mortal sin cannot become venial, by the addition of a deformity pertaining to the genus of venial sin, for the sin is not diminished if a man commit fornication in order to utter an idle word; rather is it aggravated by the additional deformity.

Nevertheless a sin which is generically mortal, can become venial by reason of the imperfection of the act, because then it does not completely fulfil the conditions of a moral act, since it is not a deliberate, but a sudden act, as is evident from what we have said above (A. 2).  This happens by a kind of subtraction, namely, of deliberate reason.  And since a moral act takes its species from deliberate reason, the result is that by such a subtraction the species of the act is destroyed.

Reply Obj. 1:  Venial differs from mortal as imperfect from perfect, even as a boy differs from a man.  But the boy becomes a man and not vice versa.  Hence the argument does not prove.

Reply Obj. 2:  If the ignorance be such as to excuse sin altogether, as the ignorance of a madman or an imbecile, then he that commits fornication in a state of such ignorance, commits no sin either mortal or venial.  But if the ignorance be not invincible, then the ignorance itself is a sin, and contains within itself the lack of the love of God, in so far as a man neglects to learn those things whereby he can safeguard himself in the love of God.

Reply Obj. 3:  As Augustine says (Contra Mendacium vii), “those things which are evil in themselves, cannot be well done for any good end.”  Now murder is the slaying of the innocent, and this can nowise be well done.  But, as Augustine states (De Lib.  Arb. i, 4, 5), the judge who sentences a thief to death, or the soldier who slays the enemy of the common weal, are not murderers. ________________________

QUESTION 89

OF VENIAL SIN IN ITSELF
(In Six Articles)

We must now consider venial sin in itself, and under this head there are six points of inquiry: 

(1) Whether venial sin causes a stain in the soul?

(2) Of the different kinds of venial sin, as denoted by “wood,” “hay,” “stubble” (1 Cor. 3:12);

(3) Whether man could sin venially in the state of innocence?

(4) Whether a good or a wicked angel can sin venially?

(5) Whether the movements of unbelievers are venial sins?

(6) Whether venial sin can be in a man with original sin alone?
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FIRST ARTICLE [I-II, Q. 89, Art. 1]