Whether the Parts of the Vegetative Soul Are Fittingly Described As
the Nutritive, Augmentative, and Generative?
Objection 1: It would seem that the parts of the vegetative soul are
not fittingly described--namely, the nutritive, augmentative, and
generative. For these are called "natural" forces. But the powers of
the soul are above the natural forces. Therefore we should not class
the above forces as powers of the soul.
Obj. 2: Further, we should not assign a particular power of the
soul to that which is common to living and non-living things. But
generation is common to all things that can be generated and
corrupted, whether living or not living. Therefore the generative
force should not be classed as a power of the soul.
Obj. 3: Further, the soul is more powerful than the body. But the
body by the same force gives species and quantity; much more,
therefore, does the soul. Therefore the augmentative power of the
soul is not distinct from the generative power.
Obj. 4: Further, everything is preserved in being by that whereby it
exists. But the generative power is that whereby a living thing
exists. Therefore by the same power the living thing is preserved.
Now the nutritive force is directed to the preservation of the living
thing (De Anima ii, 4), being "a power which is capable of preserving
whatever receives it." Therefore we should not distinguish the
nutritive power from the generative.
_On the contrary,_ The Philosopher says (De Anima ii, 2,4) that the
operations of this soul are "generation, the use of food," and (cf.
_De Anima_ iii, 9) "growth."
_I answer that,_ The vegetative part has three powers. For the
vegetative part, as we have said (A. 1), has for its object the body
itself, living by the soul; for which body a triple operation of the
soul is required. One is whereby it acquires existence, and to this
is directed the _generative_ power. Another is whereby the living
body acquires its due quantity; to this is directed the
_augmentative_ power. Another is whereby the body of a living thing
is preserved in its existence and in its due quantity; to this is
directed the _nutritive_ power.
We must, however, observe a difference among these powers. The
nutritive and the augmentative have their effect where they exist,
since the body itself united to the soul grows and is preserved by the
augmentative and nutritive powers which exist in one and the same
soul. But the generative power has its effect, not in one and the same
body but in another; for a thing cannot generate itself. Therefore the
generative power, in a way, approaches to the dignity of the sensitive
soul, which has an operation extending to extrinsic things, although
in a more excellent and more universal manner; for that which is
highest in an inferior nature approaches to that which is lowest in
the higher nature, as is made clear by Dionysius (Div. Nom. vii).
Therefore, of these three powers, the generative has the greater
finality, nobility, and perfection, as the Philosopher says (De Anima
ii, 4), for it belongs to a thing which is already perfect to "produce
another like unto itself." And the generative power is served by the
augmentative and nutritive powers; and the augmentative power by the
nutritive.
Reply Obj. 1: Such forces are called natural, both because they
produce an effect like that of nature, which also gives existence,
quantity and preservation (although the above forces accomplish these
things in a more perfect way); and because those forces perform their
actions instrumentally, through the active and passive qualities,
which are the principles of natural actions.
Reply Obj. 2: Generation of inanimate things is entirely from an
extrinsic source; whereas the generation of living things is in a
higher way, through something in the living thing itself, which is
the semen containing the principle productive of the body. Therefore
there must be in the living thing a power that prepares this semen;
and this is the generative power.
Reply Obj. 3: Since the generation of living things is from a semen,
it is necessary that in the beginning an animal of small size be
generated. For this reason it must have a power in the soul, whereby
it is brought to its appropriate size. But the inanimate body is
generated from determinate matter by an extrinsic agent; therefore
it receives at once its nature and its quantity, according to the
condition of the matter.
Reply Obj. 4: As we have said above (A. 1), the operation of the
vegetative principle is performed by means of heat, the property of
which is to consume humidity. Therefore, in order to restore the
humidity thus lost, the nutritive power is required, whereby the food
is changed into the substance of the body. This is also necessary for
the action of the augmentative and generative powers.
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