Whether a venial sin can become mortal?

❌ Objection 1 : It would seem that a venial sin can become a mortal sin. For Augustine in explaining the words of Jn. 3:36: "He that believeth not the Son, shall not see life," says (Tract. xii in Joan.): "The slightest," i.e. venial, "sins kill if we make little of them." Now a sin is called mortal through causing the spiritual death of the soul. Therefore a venial sin can become mortal.

❌ Objection 2 : Further, a movement in the sensuality before the consent of reason, is a venial sin, but after consent, is a mortal sin, as stated above (Question [74], Article [8], ad 2). Therefore a venial sin can become mortal.

❌ Objection 3 : Further, venial and mortal sin differ as curable and incurable disease, as stated above (Article [1]). But a curable disease may become incurable. Therefore a venial sin may become mortal.

❌ Objection 4 : Further, a disposition may become a habit. Now venial sin is a disposition to mortal, as stated (Article [3]). Therefore a venial sin can become mortal.