4, 6), can be moved by
two things: first by its object, inasmuch as the apprehended
appetible is said to move the appetite: secondly by that agent which
moves the will inwardly to will, and this is no other than the will
itself, or God, as was shown above (Q. 9, AA. 3, 4, 6). Now God
cannot be the cause of sin, as stated above (Q. 79, A. 1). Therefore
it follows that in this respect, a man's will alone is directly the
cause of his sin.

As regards the object, a thing may be understood as moving the will
in three ways. First, the object itself which is proposed to the
will: thus we say that food arouses man's desire to eat. Secondly, he
that proposes or offers this object. Thirdly, he that persuades the
will that the object proposed has an aspect of good, because he also,
in a fashion, offers the will its proper object, which is a real or
apparent good of reason. Accordingly, in the first way the sensible
things, which approach from without, move a man's will to sin. In the
second and third ways, either the devil or a man may incite to sin,
either by offering an object of appetite to the senses, or by
persuading the reason. But in none of these three ways can anything
be the direct cause of sin, because the will is not, of necessity,
moved by any object except the last end, as stated above (Q. 10, AA.
1, 2). Consequently neither the thing offered from without, nor he
that proposes it, nor he that persuades, is the sufficient cause of
sin. Therefore it follows that the devil is a cause of sin, neither
directly nor sufficiently, but only by persuasion, or by proposing
the object of appetite.

Reply Obj. 1: All these, and other like authorities, if we meet with
them, are to be understood as denoting that the devil induces man to
affection for a sin, either by suggesting to him, or by offering him
objects of appetite.

Reply Obj. 2: This comparison is true in so far as the devil is
somewhat the cause of our sins, even as God is in a certain way the
cause of our good actions, but does not extend to the mode of
causation: for God causes good things in us by moving the will
inwardly, whereas the devil cannot move us in this way.

Reply Obj. 3: God is the universal principle of all inward movements
of man; but that the human will be determined to an evil counsel, is
directly due to the human will, and to the devil as persuading or
offering the object of appetite.
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SECOND ARTICLE [I-II, Q. 80, Ar