Whether Besides the Intellectual Soul There Are in Man Other Souls
Essentially Different from One Another?
Objection 1: It would seem that besides the intellectual soul there
are in man other souls essentially different from one another, such
as the sensitive soul and the nutritive soul. For corruptible and
incorruptible are not of the same substance. But the intellectual
soul is incorruptible; whereas the other souls, as the sensitive and
the nutritive, are corruptible, as was shown above (Q. 75, A. 6).
Therefore in man the essence of the intellectual soul, the sensitive
soul, and the nutritive soul, cannot be the same.
Obj. 2: Further, if it be said that the sensitive soul in man is
incorruptible; on the contrary, "corruptible and incorruptible differ
generically," says the Philosopher, _Metaph._ x (Did. ix, 10). But
the sensitive soul in the horse, the lion, and other brute animals,
is corruptible. If, therefore, in man it be incorruptible, the
sensitive soul in man and brute animals will not be of the same
genus. Now an animal is so called from its having a sensitive soul;
and, therefore, "animal" will not be one genus common to man and
other animals, which is absurd.
Obj. 3: Further, the Philosopher says, _Metaph._ viii (Did. vii, 2),
that the genus is taken from the matter, and difference from the
form. But "rational," which is the difference constituting man, is
taken from the intellectual soul; while he is called "animal" by
reason of his having a body animated by a sensitive soul. Therefore
the intellectual soul may be compared to the body animated by a
sensitive soul, as form to matter. Therefore in man the intellectual
soul is not essentially the same as the sensitive soul, but
presupposes it as a material subject.
_On the contrary,_ It is said in the book _De Ecclesiasticis
Dogmatibus_ xv: "Nor do we say that there are two souls in one man,
as James and other Syrians write; one, animal, by which the body is
animated, and which is mingled with the blood; the other, spiritual,
which obeys the reason; but we say that it is one and the same soul
in man, that both gives life to the body by being united to it, and
orders itself by its own reasoning."
_I answer that,_ Plato held that there were several souls in one body,
distinct even as to organs, to which souls he referred the different
vital actions, saying that the nutritive power is in the liver, the
concupiscible in the heart, and the power of knowledge in the brain.
Which opinion is rejected by Aristotle (De Anima ii, 2), with regard
to those parts of the soul which use corporeal organs; for this
reason, that in those animals which continue to live when they have
been divided in each part are observed the operations of the soul, as
sense and appetite. Now this would not be the case if the various
principles of the soul's operations were essentially different, and
distributed in the various parts of the body. But with regard to the
intellectual part, he seems to leave it in doubt whether it be "only
logically" distinct from the other parts of the soul, "or also
locally."
The opinion of Plato might be maintained if, as he held, the soul was
supposed to be united to the body, not as its form, but as its motor.
For it involves nothing unreasonable that the same movable thing be
moved by several motors; and still less if it be moved according to
its various parts. If we suppose, however, that the soul is united to
the body as its form, it is quite impossible for several essentially
different souls to be in one body. This can be made clear by three
different reasons.
In the first place, an animal would not be absolutely one, in which
there were several souls. For nothing is absolutely one except by one
form, by which a thing has existence: because a thing has from the
same source both existence and unity; and therefore things which are
denominated by various forms are not absolutely one; as, for instance,
"a white man." If, therefore, man were _living_ by one form, the
vegetative soul, and _animal_ by another form, the sensitive soul, and
_man_ by another form, the intellectual soul, it would follow that man
is not absolutely one. Thus Aristotle argues, _Metaph._ viii (Did. vii,
6), against Plato, that if the idea of an animal is distinct from the
idea of a biped, then a biped animal is not absolutely one. For this
reason, against those who hold that there are several souls in the
body, he asks (De Anima i, 5), "what contains them?"--that is, what
makes them one? It cannot be said that they are united by the one
body; because rather does the soul contain the body and make it one,
than the reverse.
Secondly, this is proved to be impossible by the manner in which one
thing is predicated of another. Those things which are derived from
various forms are predicated of one another, either accidentally, (if
the forms are not ordered to one another, as when we say that
something white is sweet), or essentially, in the second manner of
essential predication, (if the forms are ordered one to another, the
subject belonging to the definition of the predicate; as a surface is
presupposed to color; so that if we say that a body with a surface is
colored, we have the second manner of essential predication.)
Therefore, if we have one form by which a thing is an animal, and
another form by which it is a man, it follows either that one of these
two things could not be predicated of the other, except accidentally,
supposing these two forms not to be ordered to one another--or that
one would be predicated of the other according to the second manner of
essential predication, if one soul be presupposed to the other. But
both of these consequences are clearly false: because "animal" is
predicated of man essentially and not accidentally; and man is not
part of the definition of an animal, but the other way about.
Therefore of necessity by the same form a thing is animal and man;
otherwise man would not really be the thing which is an animal, so
that animal can be essentially predicated of man.
Thirdly, this is shown to be impossible by the fact that when one
operation of the soul is intense it impedes another, which could never
be the case unless the principle of action were essentially one.
We must therefore conclude that in man the sensitive soul, the
intellectual soul, and the nutritive soul are numerically one soul.
This can easily be explained, if we consider the differences of
species and forms. For we observe that the species and forms of things
differ from one another, as the perfect and imperfect; as in the order
of things, the animate are more perfect than the inanimate, and
animals more perfect than plants, and man than brute animals; and in
each of these genera there are various degrees. For this reason
Aristotle, _Metaph._ viii (Did. vii, 3), compares the species of things
to numbers, which differ in species by the addition or subtraction of
unity. And (De Anima ii, 3) he compares the various souls to the
species of figures, one of which contains another; as a pentagon
contains and exceeds a tetragon. Thus the intellectual soul contains
virtually whatever belongs to the sensitive soul of brute animals, and
to the nutritive souls of plants. Therefore, as a surface which is of
a pentagonal shape, is not tetragonal by one shape, and pentagonal by
another--since a tetragonal shape would be superfluous as contained
in the pentagonal--so neither is Socrates a man by one soul, and
animal by another; but by one and the same soul he is both animal and
man.
Reply Obj. 1: The sensitive soul is incorruptible, not by reason of
its being sensitive, but by reason of its being intellectual. When,
therefore, a soul is sensitive only, it is corruptible; but when with
sensibility it has also intellectuality, it is incorruptible. For
although sensibility does not give incorruptibility, yet it cannot
deprive intellectuality of its incorruptibility.
Reply Obj. 2: Not forms, but composites, are classified either
generically or specifically. Now man is corruptible like other
animals. And so the difference of corruptible and incorruptible which
is on the part of the forms does not involve a generic difference
between man and the other animals.
Reply Obj. 3: The embryo has first of all a soul which is merely
sensitive, and when this is removed, it is supplanted by a more
perfect soul, which is both sensitive and intellectual: as will be
shown further on (Q. 118, A. 2, ad 2).
Reply Obj. 4: We must not consider the diversity of natural things as
proceeding from the various logical notions or intentions, which flow
from our manner of understanding, because reason can apprehend one
and the same thing in various ways. Therefore since, as we have said,
the intellectual soul contains virtually what belongs to the
sensitive soul, and something more, reason can consider separately
what belongs to the power of the sensitive soul, as something
imperfect and material. And because it observes that this is
something common to man and to other animals, it forms thence the
notion of the genus; while that wherein the intellectual soul
exceeds the sensitive soul, it takes as formal and perfecting;
thence it gathers the "difference" of man.
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