Whether sin has an internal cause?

❌ Objection 1 : It would seem that sin has no internal cause. For that which is within a thing is always in it. If therefore sin had an internal cause, man would always be sinning, since given the cause, the effect follows.

❌ Objection 2 : Further, a thing is not its own cause. But the internal movements of a man are sins. Therefore they are not the cause of sin.

❌ Objection 3 : Further, whatever is within man is either natural or voluntary. Now that which is natural cannot be the cause of sin, for sin is contrary to nature, as Damascene states (De Fide Orth. ii, 3; iv, 21); while that which is voluntary, if it be inordinate, is already a sin. Therefore nothing intrinsic can be the cause of the first sin.