80 Moral Philosophy: Ideas of Good and Evil, Right and Wronga way as to stand in need of nothing beyond itself.” God is the
only absolute substance. All other substances are His creation.
Since the substance called God, and the substance called the
universe cannot be the same, he concludes that the universe is
composed of two finite substances, mind and matter. Each
substance has a primary attribute. The mind’s principal attribute
is thinking, the body’s principal attribute is extension— it occu
pies space. A thing must be one or the other. The mind (soul)
cannot occupy space; the body (corporeal) cannot think.
Body, matter, or material (Descartes used the terms inter
changeably) is that which has extension, which is his term for
length, breadth, and thickness. It has motion, the force which
causes bodies to move from one place to another. All laws of
nature are laws of motion, therefore all knowledge of the laws of
motion would enable one to understand the universe. He as
sumes the reality of the physical universe because an infinite,
omniscient, omnipotent God would not deceive his creation—
man.
Mind, the other substance, is the thinking substance he thought
of as independent of matter. The mind of man, the soul, is what
makes man different from animals. Animals live according to
the laws of motion, man has free will. When the body dies, the
soul lives on.
The problem, of course, is how does one reconcile this
dualism of mind and matter, this mechanistic idea of a physical
universe and the idea of a soul which is free and independent. At
first Descartes avoided the problem. But with the soul free to
move the body as well as to think, and the body which clearly
seems to affect the mind at times, the problem called for an
answer. He developed the theory that the extended substance and
the thinking substance affect each other through the “animal
fluids” which surround the pineal gland, an organ at the base of
the brain. This weak explanation caused him, later in life, to
claim that the interaction was caused by “constant intervention
of God.”
Although he tried to avoid it, Descartes eventually had to
admit that the body is not completely commanded by the mind.
Although he continued to believe that the goal of man should be
to free the mind from the influence of the body and other outside
forces, he realized that this ideal could probably not be fully