Descartes is famed by is familiar notion, "I think therefore I am (Cogito,
ergo sum.)." It is a conclusion he has reached in his second meditation
after much deliberation on the existence of anything certain. After he discovers
his ability to doubt and to understand , he is able to substantiate his
necessary existence as a consequence. What we doubt or understand may not
ultimately correspond, but we can never be uncertain that we are in the process
of thought. This idea is a major component in DescartesÕ proof of the external
world. He relies on the existence of a non-deceiving God to ensure that an
external world exists after calling it into doubt by the invocation of the dream
argument. In this argument, Descartes suggests the possibility that none of our
ideas are caused by external objects and therefore, such objects may not exist.
He also raises the idea of a demon that may deceive us and allow us to perceive
what is not really there. Although he assures himself of his own existence by
his modes of thought, he remains uncertain of the reality of an external world.
He doubts whether there is anything of material substance that provokes thought
within him rather than it being conceived in his mind completely independent of
anything else. Descartes then considers those reasons that have inclined him to
believe these material things exist in the past. "I know by experience that
these ideas do not depend upon my will, nor consequently upon myself, for often
I notice them against my will... I feel heat, and therefore I believe that this
feeling or idea of heat comes to me from something other than myself, namely
from the fire I am near. Nothing is more obvious than the judgment that this
object (rather than something else) grafts its likeness on to me." Since
however, he has called upon anything to be false that provokes any doubt he does
not believe this explanation to be enough for the proof of the external world.
Relying on this sort of natural impulse has led him astray in the past, so what
is to keep it from happening all the time. He also calls upon the dream argument
in this instance. Ideas come to be in dreams independent of external objects and
perhaps this is true of ideas when we are awake. It seems that Descartes finds
it necessary to first establish the existence of a non-deceiving God before he
can be assured of the existence of anything beyond himself and his mode of
thought. He does this by the rationalization that his perception of God is that
of a perfect being. In order for a being to be perfect it must exist. Since he
himself is an imperfect being, he can not conceive the idea of perfection on his
own. Therefore, it must have come from some other faculty that must be perfect,
which is God. It is after his proof of the existence of God that Descartes comes
to accept that clear and distinct ideas can be trusted. After this deliberation
his process of coming to the existence of an external world seems rather direct.
I have the clear perception that material objects exist. Since I have already
determined that God is not deceiving me nor my perceptions, my perceptions can
be trusted as being actual. If my perceptions of material objects and an
external world are actual, then they must exist. But this external reality is
different from our reality of thought. It becomes dualistic by the idea of two
separate substances. Descartes establishes a sort of isomorphic state between
thought, or the mind, and extension, or matter. The mind takes up no space. It
consists of the senses and all modes of thought. Matter, however, takes up
space. It can be divided into smaller and smaller components, but it, unlike the
mind, has no consciousness. Both, he infers have God as their source because
God, alone, exists independent of anything else. But, the substances do not have
any contact with each other. Thought is independent of matter just as matter is
independent of thought. But, although the two are indeed completely independent
of each other, there is constant interaction between the two. This is the
essence of DecartesÕ philosophy of dualism. We as humans, consist of both and
are therefore, dualistic creatures. We have a mind and we also take up space.
Both are crucial to our elements of being, but we will grow old and we can be
physically debilitated. But, so long we continue to think and have
consciousness, two plus two will always be four and a mile will still be a mile.