sometimes they
arise from the movement of our free-will."

_I answer that,_ One thing can be the cause of another in two ways;
directly and indirectly. Indirectly as when an agent is the cause of
a disposition to a certain effect, it is said to be the occasional
and indirect cause of that effect: for instance, we might say that he
who dries the wood is the cause of the wood burning. In this way we
must admit that the devil is the cause of all our sins; because he it
was who instigated the first man to sin, from whose sin there
resulted a proneness to sin in the whole human race: and in this
sense we must take the words of Damascene and Dionysius.

But a thing is said to be the direct cause of something, when its
action tends directly thereunto. And in this way the devil is not the
cause of every sin: for all sins are not committed at the devil's
instigation, but some are due to the free-will and the corruption of
the flesh. For, as Origen says (Peri Archon iii), even if there were
no devil, men would have the desire for food and love and such like
pleasures; with regard to which many disorders may arise unless those
desires are curbed by reason, especially if we presuppose the
corruption of our natures. Now it is in the power of the free-will to
curb this appetite and keep it in order. Consequently there is no need
for all sins to be due to the instigation of the devil. But those sins
which are due thereto man perpetrates "through being deceived by the
same blandishments as were our first parents," as Isidore says (De
Summo Bono ii).

Thus the answer to the first objection is clear.

Reply Obj. 2: When man commits sin without being thereto instigated
by the devil, he nevertheless becomes a child of the devil thereby,
in so far as he imitates him who was the first to sin.

Reply Obj. 3: Man can of his own accord fall into sin: but he cannot
advance in merit without the Divine assistance, which is borne to man
by the ministry of the angels. For this reason the angels take part
in all our good works: whereas all our sins are not due to the
demons' instigation. Nevertheless there is no kind of sin which is
not sometimes due to the demons' suggestion.
_______________________

FOURTH ARTICLE [I, Q. 114, Art. 4]

Whether Demons Can Lead Men Astray by Means of Real Miracles?

Objection 1: It would seem that the demons cannot lead men astray by
means of real miracles. For the activity of the demons will show
itself e