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with forms free of matter is not a question of value, but a question
of logic.
Aquinas regarded the souls of human beings, and indeed of all
living things, as particular instances of substantial forms. As an
Aristotelian he considered that animals and vegetables had souls no
less than human beings: a soul was simply the principle of life in
152 Aquinas on Mind
organic living beings, and there are many non-human organisms.
The special privilege of human beings was not their possession of a
soul, but their possession of a rational or intellectual soul. Now
human beings grow and take nourishment, just as vegetables do;
they see and taste and run and sleep just as animals do. Does this
mean that they have a vegetable and animal soul as well as a
human soul?
Many of Aquinas contemporaries answered this question in the
affirmative. They held that in the human being there was not just a
single form, the intellectual soul, but also animal and vegetable souls;
and for good measure some of them added a further form, a form
which made a human being a bodily being. This was a form of
corporeality which human beings had in common with stocks and
stones just as they had a sensitive soul in common with animals and
a vegetative soul in common with plants.
Aquinas rejected this proliferation of substantial forms. He
maintained that in a human being there was only a single substantial
form: the rational soul. It was that soul which controlled the animal
and vegetable functions of human beings, and it was that soul which
made a human body the kind of body it was: there was no substantial
form of corporeality making a human body bodily. If there had been
a plurality of forms, he argued, one could not say that it was one and
the same human being who thought, loved, felt, heard, ate, drank,
slept and had a certain weight and size. When a human being died,
there was a substantial change; and, as in any substantial change,
there was nothing in common to the two terms of the change other
than prime matter.
The second and third articles of question seventy-six seek to
establish that there is a one-one correspondence between human
bodies and human souls. The second article rejects the suggestion
that there might be a single soul for many bodies; and the third article
rejects the suggestion that there might be many souls in a single body.
It might be thought that the one-one correspondence had already
been established in the previous discussion.
This is not entirely true, however. The first article, one might say,
established that a human being is a marriage of body and soul. But
marriage can be polygamous or polyandrous. A familiar
iconographical tradition represents souls as being female (anima,
after all, is feminine in Latin). If we follow this tradition, and think
corresondingly of the body as being male, then we can say that
the second article is directed against the polyandrous view of the
Mind and body 153
body-soul relationship, and the third article is directed against the
polygamous view. The issue has been settled in the first article only
to the extent that the underlying model of body-soul union has been
a monogamous one.
The discussion of the polyandrous view (the view of the
Averroists) contains much ingenious argument on either side. The
large number of objections and replies show that the issue was a
matter of lively debate in Aquinas time. To refute the polyandrous
view, Aquinas seeks to show that however the mind-body
relationship is conceived, it will have unacceptable consequences if
we suppose a single intellect to be united to many bodies. In every
case, he argues, if you and I share the same soul we will turn out to
be the same person.
We can illustrate his line of argument in the case of the theory
which he regards as the least implausible of the opposing views:
My thinking might differ from your thinking because of the
difference between our phantasms: I have one image of stone
and you have another. But this could only be so if the phantasm,
in its distinct individuality, was the form of the receptive
intellect. The same agent does indeed perform different actions
when differently informed: for instance, when two different
forms inform one and the same eye there are two distinct acts of
seeing. But the phantasm is not the form of the receptive
intellect, but the intelligible idea which is abstracted from the
phantasms. And from however many phantasms of the same
kind only one intelligible idea is abstracted by a single
intellect.& If therefore there was only a single intellect for all
men, the variety of phantasms in different men could not make
any difference between the thinking of one man and the
thinking of another.
(S 1, 76, 2)6
The most telling of the arguments put forward on the other side is as
follows. If what individuates souls is their one-one correspondence
with different bodies, then when the bodies die there would only be a
single soul, since what made the difference between souls has now
disappeared. To this Aquinas replied simply that if you can accept the
continued existence of the disembodied soul, you should be able also
to accept the continued individuation of the disembodied soul (S 1,
76, 2 and ad 2). Perhaps this is correct. But the conclusion to draw
154 Aquinas on Mind
might be that one should rethink one s acceptance of disembodied
existence; for the consideration of disembodied individuation brings
out in a particularly vivid way the difficulties inherent in the original
notion. No doubt, in terms of our matrimonial analogy, Aquinas
could point out that Tom s widow and Dick s widow and Harry s
widow are three different widows, in spite of Tom, Dick and Harry
all being in their graves. But to this the reply must be that women are
individuated by their husbands as wives, not as human beings.
Article three moves on from polyandry to polygamy: can a single
human being have more than one soul? The supporters of the
polygamous view are not Muslim thinkers, but Christian ones; and
indeed the theory was officially promulgated by successive
Archbishops of Canterbury, after Aquinas death. Aquinas argument
for the single soul view is simple: it is that if a human being had three
different souls, he would be three different animals. His consistent
principle is: one substance, one substantial form. On the basis of this
Aquinas goes on to argue, in article four, that not only can a human
being not have more than one soul, but it is also impossible to have
any extra substantial forms (for example, the forms of the chemical
substances in the body) in addition to the soul.
If there were some other substantial form pre-existing in matter
when the intellectual soul was joined to the body, then the soul would
merely be introducing an accidental change into the body, and not
giving it existence as the kind of thing it is. Likewise, the departure
of the soul would not be the cessation of the life of the human being,
but merely an insubstantial change.
So we must say that there is no substantial form in a human
being other than the intellectual soul, and that just as that soul
has the power to do all that the sensory and the nutritive soul
can do, so too it has the powers to effect whatever in other beings
is done by the more elementary forms.
(S 1, 76, 4)7
A point which is closely connected to this one is the thesis that the
whole soul is in every part of the human body. Descartes believed
that the soul was united to the body at a very particular point: the
pineal gland. Many modern thinkers, if they are willing to talk of
the soul at all, conceive it as having its seat in the brain, or in the
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