THE MEDIEVAL WORLD 93
no way of knowing that it had not.
Aquinas believes that there are
a number of other doctrines central
to Christianity that the ancient
philosophers did not know and
could not have known—such as
the belief that God is a Trinity
made up of three persons, and that
one person of the Trinity, the Son,
became a human. But in Aquinas’s
opinion, whenever humans reason
correctly, they cannot come to any
conclusion which contradicts
Christian doctrine. This is because
both human reason and Christian
teaching come from the same
source—God—and so they can
never contradict each other.
Aquinas taught in convents
and universities in France and Italy,
and the idea that human reason
could never conflict with Christian
doctrine often placed him in fierce
conflict with some of his academic
contemporaries, especially those
who specialized in the sciences,
which at the time were derived
from the work of Aristotle. Aquinas
accused his fellow scholars of
accepting certain positions on
faith—for example, the position
that we each have an immortal
soul—but of saying at the same
time that according to reason,
these positions could be shown
to be wrong.How we gain knowledge
Aquinas keeps to these principles
throughout his work, but they are
particularly clear in two central
areas of his thought: his account
of how we gain knowledge and his
treatment of the relation between
mind and body. According to
Aquinas, human beings acquire
knowledge through using their
senses: sight, hearing, smell, touch,
and taste. These sense-impressions,
however, only tell us what things
are like superficially. For example,
from where John sits, he has a visual
impression of a tree-shaped object,
which is green and brown. I, on the
other hand, am standing next to the
tree, and can feel the roughness of
its bark and smell the scent of the
forest. If John and I were dogs, our
knowledge of the tree would be
limited to these sense-impressions.
But as human beings we are able to
go beyond them and grasp what a
tree is in a rational way, defining it
and distinguishing it from othertypes of plants and of living things.
Aquinas calls this “intellectual
knowledge”, because we gain it
by using the innate power of our
intellect to seize, on the basis of
sense-impressions, the reality that
lies behind them. Animals other
than humans lack this inborn
capacity, which is why their
knowledge cannot stretch beyond
the senses. All of our scientific
understanding of the world is based
on this intellectual knowledge.
Aquinas’s theory of knowledge
owes much to Aristotle, although
he clarifies and elaborates upon ❯❯Aristotle believed that the universe was infinite,
as each hour and day is succeed by another. Aquinas
disagreed, believing that the universe had a beginning,
but his respect for Aristotle’s philosophy led him to
argue that Aristotle could have been correct.
We should see whether
there is a contradiction
between something being
created by God, and its
existing forever.
Thomas Aquinas