NINTH ARTICLE [I-II, Q. 17, Art. 9]

Whether the Acts of the External Members Are Commanded?

Objection 1:  It would seem that the members of the body do not obey reason as to their acts.  For it is evident that the members of the body are more distant from the reason, than the powers of the vegetal soul.  But the powers of the vegetal soul do not obey reason, as stated above (A. 8).  Therefore much less do the members of the body obey.

Obj. 2:  Further, the heart is the principle of animal movement.  But the movement of the heart is not subject to the command of reason:  for Gregory of Nyssa [Nemesius, De Nat.  Hom. xxii.] says that “the pulse is not controlled by reason.”  Therefore the movement of the bodily members is not subject to the command of reason.

Obj. 3:  Further, Augustine says (De Civ.  Dei xiv, 16) that “the movement of the genital members is sometimes inopportune and not desired; sometimes when sought it fails, and whereas the heart is warm with desire, the body remains cold.”  Therefore the movements of the members are not obedient to reason.

On the contrary, Augustine says (Confess. viii, 9):  “The mind commands a movement of the hand, and so ready is the hand to obey, that scarcely can one discern obedience from command.”

I answer that, The members of the body are organs of the soul’s powers.  Consequently according as the powers of the soul stand in respect of obedience to reason, so do the members of the body stand in respect thereof.  Since then the sensitive powers are subject to the command of reason, whereas the natural powers are not; therefore all movements of members, that are moved by the sensitive powers, are subject to the command of reason; whereas those movements of members, that arise from the natural powers, are not subject to the command of reason.

Reply Obj. 1:  The members do not move themselves, but are moved through the powers of the soul; of which powers, some are in closer contact with the reason than are the powers of the vegetal soul.

Reply Obj. 2:  In things pertaining to intellect and will, that which is according to nature stands first, whence all other things are derived:  thus from the knowledge of principles that are naturally known, is derived knowledge of the conclusions; and from volition of the end naturally desired, is derived the choice of the means.  So also in bodily movements the principle is according to nature.  Now the principle of bodily movements begins with the movement of the heart.  Consequently the movement of the heart is according to nature, and not according to the will:  for like a proper accident, it results from life, which follows from the union of soul and body.  Thus the movement of heavy and light things results from their substantial form:  for which reason they are said to be moved by their generator, as the Philosopher states (Phys. viii, 4).  Wherefore this movement is called “vital.”  For which reason Gregory of Nyssa (Nemesius, De Nat.  Hom. xxii) says that, just as the movement of generation and nutrition does not obey reason, so neither does the pulse which is a vital movement.  By the pulse he means the movement of the heart which is indicated by the pulse veins.