shment must be inflicted for the sake of good.
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QUESTION 80

OF THE CAUSE OF SIN, AS REGARDS THE DEVIL
(In Four Articles)

We must now consider the cause of sin, as regards the devil; and
under this head there are four points of inquiry:

(1) Whether the devil is directly the cause of sin?

(2) Whether the devil induces us to sin, by persuading us inwardly?

(3) Whether he can make us sin of necessity?

(4) Whether all sins are due to the devil's suggestion?
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FIRST ARTICLE [I-II, Q. 80, Art. 1]

Whether the Devil Is Directly the Cause of Man's Sinning?

Objection 1: It would seem that the devil is directly the cause of
man's sinning. For sin consists directly in an act of the appetite.
Now Augustine says (De Trin. iv, 12) that "the devil inspires his
friends with evil desires"; and Bede, commenting on Acts 5:3, says
that the devil "draws the mind to evil desires"; and Isidore says (De
Summo Bono ii, 41; iii, 5) that the devil "fills men's hearts with
secret lusts." Therefore the devil is directly the cause of sin.

Obj. 2: Further, Jerome says (Contra Jovin. ii, 2) that "as God is
the perfecter of good, so is the devil the perfecter of evil." But
God is directly the cause of our good. Therefore the devil is
directly the cause of our sins.

Obj. 3: Further, the Philosopher says in a chapter of the _Eudeme[a]n
Ethics_ (vii, 18): "There must needs be some extrinsic principle of
human counsel." Now human counsel is not only about good things but
also about evil things. Therefore, as God moves man to take good
counsel, and so is the cause of good, so the devil moves him to take
evil counsel, and consequently is directly the cause of sin.

_On the contrary,_ Augustine proves (De Lib. Arb. i, 11) that
"nothing else than his own will makes man's mind the slave of his
desire." Now man does not become a slave to his desires, except
through sin. Therefore the cause of sin cannot be the devil, but
man's own will alone.

_I answer that,_ Sin is an action: so that a thing can be directly
the cause of sin, in the same way as anyone is directly the cause of
an action; and this can only happen by moving that action's proper
principle to act. Now the proper principle of a sinful action is the
will, since every sin is voluntary. Consequently nothing can be
directly the cause of sin, except that which can move the will to act.

Now the will, as stated above (Q. 9, AA. 3,