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.
Reply Obj. 3: As Augustine says (De Civ. Dei xiv, 17, 20) it is in
punishment of sin that the movement of these members does not obey
reason: in this sense, that the soul is punished for its rebellion
against God, by the insubmission of that member whereby original sin
is transmitted to posterity.
But because, as we shall state later on, the effect of the sin of our
first parent was that his nature was left to itself, through the
withdrawal of the supernatural gift which God had bestowed on man, we
must consider the natural cause of this particular member's
insubmission to reason. This is stated by Aristotle (De Causis Mot.
Animal.) who says that "the movements of the heart and of the organs
of generation are involuntary," and that the reason of this is as
follows. These members are stirred at the occasion of some
apprehension; in so far as the intellect and imagination represent
such things as arouse the passions of the soul, of which passions
these movements are a consequence. But they are not moved at the
command of the reason or intellect, because these movements are
conditioned by a certain natural change of heat and cold, which
change is not subject to the command of reason. This is the case with
these two organs in particular, because each is as it were a separate
animal being, in so far as it is a principle of life; and the
principle is virtually the whole. For the heart is the principle of
the senses; and from the organ of generation proceeds the seminal
virtue, which is virtually the entire animal. Consequently they have
their proper movements naturally: because principles must needs be
natural, as stated above (Reply Obj. 2).
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