sed
as appetible to the senses, and because the appetite is inclined,
that the reason sometimes fails to consider the due rule, so that the
will produces the act of sin. Since therefore the movements that
precede it are not always actual, neither is man always actually
sinning.

Reply Obj. 2: It is not true that all the internal acts belong to the
substance of sin, for this consists principally in the act of the
will; but some precede and some follow the sin itself.

Reply Obj. 3: That which causes sin, as a power produces its act, is
natural; and again, the movement of the sensitive part, from which
sin follows, is natural sometimes, as, for instance, when anyone sins
through appetite for food. Yet sin results in being unnatural from
the very fact that the natural rule fails, which man, in accord with
his nature, ought to observe.
________________________

THIRD ARTICLE [I-II, Q. 75, Art. 3]

Whether Sin Has an External Cause?

Objection 1: It would seem that sin has no external cause. For sin is
a voluntary act. Now voluntary acts belong to principles that are
within us, so that they have no external cause. Therefore sin has no
external cause.

Obj. 2: Further, as nature is an internal principle, so is the will.
Now in natural things sin can be due to no other than an internal
cause; for instance, the birth of a monster is due to the corruption
of some internal principle. Therefore in the moral order, sin can
arise from no other than an internal cause. Therefore it has no
external cause.

Obj. 3: Further, if the cause is multiplied, the effect is
multiplied. Now the more numerous and weighty the external
inducements to sin are, the less is a man's inordinate act imputed
to him as a sin. Therefore nothing external is a cause of sin.

_On the contrary,_ It is written (Num. 21:16): "Are not these they,
that deceived the children of Israel by the counsel of Balaam, and
made you transgress against the Lord by the sin of Phogor?" Therefore
something external can be a cause of sin.

_I answer that,_ As stated above (A. 2), the internal cause of sin is
both the will, as completing the sinful act, and the reason, as
lacking the due rule, and the appetite, as inclining to sin.
Accordingly something external might be a cause of sin in three ways,
either by moving the will itself immediately, or by moving the
reason, or by moving the sensitive appetite. Now, as stated above (Q.
9, A. 6; Q. 10, A. 4), none can move t