The Philosophy Book

91

Aquinas is flanked by Aristotle
and Plato in The Triumph of Thomas
Aquinas. His understanding of ancient
philosophy was considered greater than
that of Averroes, who lies at his feet.

See also: Aristotle 56–63 ■ Avicenna 76–79 ■ Averroes 82–83 ■ John Philoponus 332 ■ John Duns Scotus 333 ■
Pierre Abélard 333 ■ William of Ockham 334 ■ Immanuel Kant 164–71

THE MEDIEVAL WORLD

There never was

a time when there

was not motion.

Aristotle

Aristotle says that

the universe has

always existed.

The Bible says that

the universe has not

always existed.

The world did have a

beginning, but God could

have created it in such a way

that it existed eternally.

infinity as a point of departure, but
turned them against his view of
the universe as eternal.

An infinity of humans
According to Aristotle, the infinite
is what has no limit. For instance,
the sequence of numbers is infinite,
because for each number, there is
another higher number that follows.
Similarly, the universe has existed
for an infinite time, because for each
day, there is a preceding day. In
Aristotle’s opinion, however, this is
a “potential” infinity, as these days
do not coexist at the same time;
an “actual” infinity—in which an
infinite number of things all exist
at the same time—is impossible.
Philoponus and his 13th-century
followers, however, think that this
argument presents problems that
Aristotle had not noticed. They point
to the fact that he believes that all

the types of living beings in the

universe have always existed. If this

were true, they say, it would mean

that there were already an infinite

number of human beings by the

time Socrates was born—because

if they have always existed, they

existed then. But since Socrates’

time, many more humans have been

born, and so the number of humans

born up until now must be greater

than infinity. But no number can

be greater than infinity.

In addition, these writers add,

Christian thinkers believe that

human souls are immortal. If this

is so, and an infinite number of

humans has already existed, there

must be an infinite number of human

souls in existence now. So there is

an actual infinity of souls, not a

potential infinity; and Aristotle has

said actual infinity is impossible.

With these two arguments,

using Aristotle’s own principles as

a starting point, Philoponus and his

followers were confident they had

demonstrated that the universe

cannot always have existed.

Aristotle was therefore wrong; the

universe is not eternal, and this fits

perfectly with the Christian

doctrine that God created the world.

Aquinas has little time for this

line of reasoning. He points out that

the universe could have existed for

ever but that species such as

humans and other animals might

have had a beginning, and so the

difficulties raised by Philoponus

and his followers can be avoided.

Despite his defence of Aristotle’s

reasoning, Aquinas does not ❯❯