Second Question: On the Exterior Causes of Sins

St. Thomas, I-II, q. 75, a. 3; De Malo q. 3, a. 3.

478. The exterior cause of sin is that which moves its interior cause, whether the will or reason or the sensitive appetite. No one can move the will immediately except God, who is not the cause of sin but permits it; man and the devil can move reason, by persuading to sin; exterior objects, for example, apprehended in themselves or in the imagination, move the sensitive appetite. Yet nothing so moves the will that it necessarily sins.