I answer that, The subject of a sin is chiefly that part of the soul to which the motive cause of that sin primarily pertains:  thus if the motive cause of a sin is sensual pleasure, which regards the concupiscible power through being its proper object, it follows that the concupiscible power is the proper subject of that sin.  Now it is evident that original sin is caused through our origin.  Consequently that part of the soul which is first reached by man’s origin, is the primary subject of original sin.  Now the origin reaches the soul as the term of generation, according as it is the form of the body:  and this belongs to the soul in respect of its essence, as was proved in the First Part (Q. 76, A. 6).  Therefore the soul, in respect of its essence, is the primary subject of original sin.

Reply Obj. 1:  As the motion of the will of an individual reaches to the soul’s powers and not to its essence, so the motion of the will of the first generator, through the channel of generation, reaches first of all to the essence of the soul, as stated.

Reply Obj. 2:  Even original justice pertained radically to the essence of the soul, because it was God’s gift to human nature, to which the essence of the soul is related before the powers.  For the powers seem to regard the person, in as much as they are the principles of personal acts.  Hence they are the proper subjects of actual sins, which are the sins of the person.

Reply Obj. 3:  The body is related to the soul as matter to form, which though it comes second in order of generation, nevertheless comes first in the order of perfection and nature.  But the essence of the soul is related to the powers, as a subject to its proper accidents, which follow their subject both in the order of generation and in that of perfection.  Consequently the comparison fails.

Reply Obj. 4:  Concupiscence, in relation to original sin, holds the position of matter and effect, as stated above (Q. 82, A. 3). ________________________

THIRD ARTICLE [I-II, Q. 83, Art. 3]

Whether Original Sin Infects the Will Before the Other Powers?

Objection 1:  It would seem that original sin does not infect the will before the other powers.  For every sin belongs chiefly to that power by whose act it was caused.  Now original sin is caused by an act of the generative power.  Therefore it seems to belong to the generative power more than to the others.

Obj. 2:  Further, original sin is transmitted through the carnal semen.  But the other powers of the soul are more akin to the flesh than the will is, as is evident with regard to all the sensitive powers, which use a bodily organ.  Therefore original sin is in them more than in the will.

Obj. 3:  Further, the intellect precedes the will, for the object of the will is only the good understood.  If therefore original sin infects all the powers of the soul, it seems that it must first of all infect the intellect, as preceding the others.