o burn_:
and such acts have for their matter and subject, the thing into which
the action passes: thus the Philosopher states (Phys. iii, text. 18)
that "movement is the act of the thing moved, caused by a mover." On
the other hand, there are acts which do not pass into external
matter, but remain in the agent, e.g. _to desire_ and _to know_: and
such are all moral acts, whether virtuous or sinful. Consequently the
proper subject of sin must needs be the power which is the principle
of the act. Now since it is proper to moral acts that they are
voluntary, as stated above (Q. 1, A. 1; Q. 18, A. 6), it follows that
the will, which is the principle of voluntary acts, both of good
acts, and of evil acts or sins, is the principle of sins. Therefore
it follows that sin is in the will as its subject.

Reply Obj. 1: Evil is said to be outside the will, because the will
does not tend to it under the aspect of evil. But since some evil is
an apparent good, the will sometimes desires an evil, and in this
sense is in the will.

Reply Obj. 2: If the defect in the apprehensive power were nowise
subject to the will, there would be no sin, either in the will, or in
the apprehensive power, as in the case of those whose ignorance is
invincible. It remains therefore that when there is in the
apprehensive power a defect that is subject to the will, this defect
also is deemed a sin.

Reply Obj. 3: This argument applies to those efficient causes whose
actions pass into external matter, and which do not move themselves,
but move other things; the contrary of which is to be observed in the
will; hence the argument does not prove.
________________________

SECOND ARTICLE [I-II, Q. 74, Art. 2]

Whether the Will Alone Is the Subject of Sin?

Objection 1: It would seem that the will alone is the subject of sin.
For Augustine says (De Duabus Anim. x, 10) that "no one sins except
by the will." Now the subject of sin is the power by which we sin.
Therefore the will alone is the subject of sin.

Obj. 2: Further, sin is an evil contrary to reason. Now good and evil
pertaining to reason are the object of the will alone. Therefore the
will alone is the subject of sin.

Obj. 3: Further, every sin is a voluntary act, because, as Augustine
states (De Lib. Arb. iii, 18) [*Cf. De Vera Relig. xiv.], "so true is
it that every sin is voluntary, that unless it be voluntary, it is no
sin at all." Now the acts of the other powers are not voluntary,
exce