Thinking is something that is intrinsic to each individual. It
is an activity one person cannot share with another. That one
has eyes that see and legs that walk is obvious, but what part of
the person is it that thinks? That is not obvious. For
Aristotle it was the mind that did the thinking. To think of
something, he said, was for the mind to become what is thought
of. Thus he said that mind was made up of thoughts. Prior to
thinking the mind was nothing. In fact it did not become
something of its own until it thought of itself. However, to
think of something is not the same as to have knowledge
One can think of what one has encountered in experience. But
experience, in an Aristotelian sense, is only of things and
things are constantly changing, knowledge can only of what can
not be other than it is. In other words of what is not changing.
As a result knowledge must be extracted from experience, from our
experience of things. Aristotle's great works on logic were
designed to explain how we can accomplish this extraction.
Plato's concept of knowledge is not of experienced things at all,
but of the unchanging ideal forms. They cannot be known directly
in this world, because everything in this world is constantly
changing. Experiencing something merely reminds us of the ideal
forms. These are developed through recollection by the soul of
the forms that were known prior to its entry into the body. This
makes that part of the person that does the thinking divine as
well as a part of its soul.
Augustine's theory of knowledge merely translated the Platonic
forms into exemplars in the mind of God that could be known
through divine illumination. The merging of these two lines of
thought in the thirteenth century was accomplished by Aquinas.
He did this through what he called the "active intellect." This,
he said, was the highest faculty of the soul. The ray of
Augustinian divine light that enables the soul of man to grasp
the eternal forms which constitute the intelligible structure of
A pure intellect would be able to experience eternal truth
directly, but humans are composites consisting of soul and body,
form and actuality. As such man gets his first contact with the
external world through the senses and this gives him the
incentive to begin thinking. For Aquinas that by which the
individual thinks is the intellectual soul, a concept derived
from Aristotle's concept of mind. It is only following
experience and through the intellectual soul that the active
intellect can extract the ideal forms from sensible experience.
. The process of understanding is the
reduction of experienced things to intelligible terms. It is a
progressive discovery of the eternal forms in the changing things
of sensual experience.
Finally, the whole intelligible structure and ultimate
explanation of the universe, abstracted from the sensible
medium in which it is first conveyed to us, fills the
intellect and fulfills the intellect's capacity for
knowledge, enlightening it with the vision of absolute
truth, in so far as a finite and embodied mind can be
If we follow the development of Thomistic Scholasticism to the
end of the sixteenth century we find that its major exponent was
the Jesuit philosopher theologian Francis Suarez. A good example
of the kind of thinking this approach leads to can be shown with
this description of Suarez' answer to the problem of contingency
and possible essences, the underlying feature of Leibnizian
metaphysics, as expressed by a modern Jesuit,.
Suarez' view is, then, this. 'Because existence is nothing
else than essence constituted in act, it follows that, just
as actual essence is formally limited by itself, or by its
own intrinsic principles, so also created existence has its
limitation from the essence, not because essence is a
potentiality in which existence is received, but because
existence is in reality nothing else but the essence
In other words, since the essence of something that exists
includes the mode of the things existence, there can be no
essence of something that does not exist. This eliminates the
possibility of possible existences. But in a world where every
possibility is known by God, and where the essence of something
includes its total existence, the denial of possible essences
denies the possibility of contingency. In other words nothing
can be different than it is. The problem of possible essences
was avoided by Descartes as he avoided many other Scholastic
arguments by his different method of pursuing understanding.
Spinoza tried to show that possible essences were an absurdity
because everything that exists does so through the nature of God.
But arguing in this fashion also denies the existence of
contingency. Descartes never gave contingency any thought and
Spinoza rejected the very idea of it. However, for man and God
to be free in the sense that they can be judged by the actions
they choose to make, contingency is essential. As we saw in the
last chapter Leibniz returned to the existence of possible
essences with his plenum of complete individual conceptions.
However, across the English channel they developed an entirely
different attitude. There the question became "So what?"
Questions of this kind cannot be solved by pure reasoning thus
they are not important. What is important is knowledge that can
change the way men live their lives, like the invention of
Gunpowder, the printing press, the magnet, and other practical