instance, if it were to give rise to great scandal
or something of the kind.

With regard to drunkenness we reply that it is a mortal sin by reason
of its genus; for, that a man, without necessity, and through the
mere lust of wine, make himself unable to use his reason, whereby he
is directed to God and avoids committing many sins, is expressly
contrary to virtue. That it be a venial sin, is due some sort of
ignorance or weakness, as when a man is ignorant of the strength of
the wine, or of his own unfitness, so that he has no thought of
getting drunk, for in that case the drunkenness is not imputed to him
as a sin, but only the excessive drink. If, however, he gets drunk
frequently, this ignorance no longer avails as an excuse, for his
will seems to choose to give way to drunkenness rather than to
refrain from excess of wine: wherefore the sin returns to its
specific nature.

Reply Obj. 2: Morose delectation is not a mortal sin except in those
matters which are mortal sins generically. In such matters, if the
delectation be not morose, there is a venial sin through imperfection
of the act, as we have said with regard to anger (ad 1): because
anger is said to be lasting, and delectation to be morose, on account
of the approval of the deliberating reason.

Reply Obj. 3: A circumstance does not make a good act to be evil,
unless it constitute the species of a sin, as we have stated above
(Q. 18, A. 5, ad 4).
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SIXTH ARTICLE [I-II, Q. 88, Art. 6]

Whether a Mortal Sin Can Become Venial?

Objection 1: It would seem that a mortal sin can become venial.
Because venial sin is equally distant from mortal, as mortal sin is
from venial. But a venial sin can become mortal, as stated above (A.
5). Therefore also a mortal sin can become venial.

Obj. 2: Further, venial and mortal sin are said to differ in this,
that he who sins mortally loves a creature more than God, while he
who sins venially loves the creature less than God. Now it may happen
that a person in committing a sin generically mortal, loves a
creature less than God; for instance, if anyone being ignorant that
simple fornication is a mortal sin, and contrary to the love of God,
commits the sin of fornication, yet so as to be ready, for the love
of God, to refrain from that sin if he knew that by committing it he
was acting counter to the love of God. Therefore his will be a venial
sin; and accordingly a mortal sin can become venial.