5. Realism and Nominalism. Plotinus' pupil Por-
phyry, to whom we have already referred, had raised
three questions about the nature of ideas in his Intro-
duction to the Categories of Aristotle.
(1) Are they beings with independent existence or do they
exist only as human concepts?
(2) If they are independent, are they material or immaterial
beings?
(3) Do they always exist in sensible objects or not?
These questions were not merely of technical philo-
sophic interest. Church dogma included some state
ments that seemed to be based on the reality of the
universals. For instance, according to Augustine, we
all sinned in Adam because we were in Adam, presum-
ably as particulars participating in a universal. Christ
again, “the second Adam,” could atone for the sins of
mankind, for He was God-made-Man. The Church
Invisible was present in all churches just as God was
entirely present in all three Persons of the Holy Trinity.
These and other dogmas seemed explicable if the ideas,
universals, were real beings, independent of anyone's
mind, and not tied to their incorporation in sensible
objects. As has been pointed out, mathematicians do
not believe that they are talking psychology. Their
subject matter behaves in a manner which no one can
make subservient to his desires or fantasies. How are
other universal ideas different?
The earliest answer to this question, which Father
Copleston, in his Medieval Philosophy (1950), has called
“exaggerated realism,” maintained that universal ideas
were not different in any way. Whenever an idea is
predicated of a subject (e.g., “This is a man”), what
is asserted is the presence of a universal. The theolog-
ical difficulties of this doctrine need not concern us
here. It is of more interest to point out that it turned
the world into an imperfect picture of an ideal design.
The man of the early Middle Ages was to direct his
eyes upward and to think of this world as useful only
as an incentive towards the ideal. In fact it led one
of its proponents, Saint Anselm (1033-1109), to argue
from the reality of an idea to the existence of that of
which it was the idea.
But logical realism was vigorously opposed by a
contemporary of Saint Anselm, Roscellinus. He is said
to have maintained that universals were only names,
a doctrine called “nominalism.” This seemed to some
to imply that when we are discussing ideas we are
talking about words. Mathematics does not appear to
be lexicography nor do any of the natural sciences.
When a physicist talks about gravitation, he may ex-
emplify his point by citing the relation between the
masses of the moon and the earth, but his real subject
matter is much more extensive. Hence the eleventh-
century clash in opinion has not been definitely settled
even today. The Middle Ages, however, were more
fortunate than we. They were given a compromise
solution by Saint Thomas Aquinas. He said that the
ideas have a being independent of things (ante rem)
in the mind of God; they have a being in things (in
rebus) as common characters; they exist in our minds
(post rem) as concepts formed by us through the powers
of abstraction. Like all compromises this raised an
additional problem: how can a single being, justice for
instance, be all three of these things and yet be one
and the same?
