The Cogito --
"I am thinking, therefore I exist."
The evil demon hypothesis is an extraordinarily powerful skeptical
hypothesis. Arguably, nothing like it can be found in earlier skeptical
literature. We have already seen that this hypothesis can call into
question everything which could not be doubted on the dream hypothesis.
So, is there anything which can withstand the overwhelming power of such
an evil demon? As it turns out, remarkably enough there is. Descartes
finally considers whether the demon can deceive him into thinking that he
exists when in fact he does not exist. Upon considering this, Descartes
concludes that he cannot be deceived into thinking that he does not exist
when in fact he does, for unless something existed there would be nothing
to deceive! So, he has found one truth which he can know with absolute
certainty! This represents the end point of what I shall call the first
application of the method of doubt and the method of analysis. Note that
once again Descartes has partitioned claims based on the understanding into
two classes, those that can be called into doubt, and those which quite
|The truths of
These can now be called into doubt -- they might all be false.
2 + 2 =
|Truths which cannot fail to be true|
therefore I exist
|Truths derived from the
Descartes' achievement in isolating a truth he cannot doubt by use of
this method is to defeat the universal skeptical claims that nothing is
known except that one knows nothing, the claim of the Academic skeptic. It
also defeats the claim that nothing is known and one does not even know
that, the claim of the Pyhronian skeptic. As one can imagine, philosophers
have raised various objections to this claim to certainty. At this point,
however, it is simply worth pausing to admire Descartes' cleverness in
defeating the skeptics.
Still, to defeat such universal skepticism, while an admirable
achievement, is the easiest objective. For one need find only one or two
truths which can be known for certain to defeat universal skepticism.
This is hardly the end of skepticism, however, since many other more
limited skeptical arguments remain to be defeated. So you know that you
exist and are a thinking thing. If you can still doubt that God does not
exist, that 17 + 8 = 25, that the moon exists some two hundred thousand
miles from Earth, you have not gotten very far with skepticism. Still,
Descartes is quite optimistic. He says: "Archimedes required only one
fixed and immovable point to move the whole world from its place, and I
too can hope for great things if I can find even one small thing which is
certain and indubitable!" (Pg.6) Descartes has now achieved that goal. In
the next unit, we will see how Descartes tries to make progress beyond the
bare knowledge that he exists!