Meditations on First Philosophy
René Descartes
Descartes and foundationalism
The problem: Late medieval philosophy had become too ambitious and subtle.
Philosophical speculations had become just that – speculations. It seemed that philosophy was
losing touch with reality. Descartes wanted to establish a firm basis for philosophy and for
faith in this new age of science.
Descartes was a keen student of the new sciences and mathematics. Created analytic
geometry ~ the ‘Cartesian coordinates’ ~ combining geometry & algebra into one. Wanted to
find new, modern foundations for knowledge.
Descartes's problem: Certainty
How can we be sure that we really know what we know? "How many were the false
beliefs that I had from my earliest youth admitted as true." His governing principle: To
withhold his assent from anything that's not entirely certain.
Sense knowledge
“I've always accepted what I've learned through the senses as most true and certain.”
Problem: Senses can be deceived.
Insane hallucinations and dreams. "There are no certain indications by which we may
clearly distinguish wakefulness from sleep.” Dreams are about corporeal things. Therefore
senses cannot be trusted.
Conclusion
Sciences that deal with composite things - physics, astronomy, medicine, etc. - are
"dubious & uncertain." On the other hand, math has some measure of certainty. "And it does
not seem possible that truths so clear and apparent can be suspected of any falsity." (169)
Like Plato, Descartes distrusts sense knowledge and finds the ideal in math.
The idea of God
Could he have created me to think there's a world, when there really is none? But God
is supremely good and would not want me deceived. Suppose some evil genius uses all his
energies to deceive me?
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What can I be certain about?
Meditation II. One Certain Thing: “Cogito, ergo sum”
I think; therefore I exist”
The immovable, Archimedean point
If nothing at all is certain, then nothing can be known. Having doubted everything –
even his own senses – Descartes needs an Archimedean point to work from.
“I shall have the right to conceive high hopes if I am happy enough to discover one
thing only which is certain and indubitable.”
His own existence
“God, or some other being, could have put reflections into my mind.”
“I have already denied that I had senses and body.”
“Am I so dependent on body and senses that I cannot exist without these?”
“Not at all; I myself did exist since I persuaded myself of something.”
Cogito
What is René Descartes?
One answer: ‘a man’…classically understood as ‘rational animal’: But what is an
animal? This is a question for biology, but Descartes has already cast doubt on all the physical
sciences. What is ‘reasonable’? This answer to the question raises even more questions.
Descartes’s analysis of his being
First, he notes that he has “face, hands, arms… bones and flesh,” in short, a body. “By
the body I understand all that which can be defined by a certain figure: something which can
be confined within a certain place…” Note that the body has geometrical properties.
But he might be deceived about his body.
What of thinking?
“I find here that thought is an attribute that belongs to me; it alone cannot be
separated from me. I am, I exist; that is certain. […] I am, however, a real thing
and really exist. But what thing? I have answered: a thing which thinks.”
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“But what then am I? A thing that thinks. What is a thing which thinks? It is a
thing which doubts, understands, affirms, denies, wills, refuses, which also
imagines and feels…”
Where we are, so far…
Descartes has doubted everything, even the existence of his own body. Therefore he
cannot know physical things. He cannot yet have scientific knowledge. One thing he does
know is that he exists, but only as a thing that thinks. All he knows are the contents of his own
mind. What will free him from his doubts about everything else?
Clear & Distinct Ideas
“But do I not then likewise know what is requisite to render me certain of a
truth?”
“I can establish it as a general rule that all things which I perceive very clearly and
distinctly are true.”
Then what about things that are outside the mind? Senses lead to error, but
mathematical science to understanding. According to sight, the sun is small, but reason shows
that it is very large.
The idea of God
I have an idea of God: “a substance that is infinite, independent, all-knowing,
all-powerful, and by which I myself and everything else have been created.”
Where did this idea come from?
“Substance” comes from my mind, because I too am a substance. But I am not
infinite. Where did this idea of ‘infinite’ come from?
Knowledge of God
He perceives the infinite by a true idea, not just the negation of the finite. Since there is
manifestly more reality in the infinite than the finite, he has that notion earlier than the finite.
Therefore, he has the notion of God before that of himself. He has not received this notion of
God through the senses, nor can he add anything to it.
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Therefore, the knowledge of God is innate – inborn.
The solution to his problems
With this knowledge that a good God must exist, Descartes can now confidently trust
his senses, because a good God would never create him to be deceived.
Compare Descartes with other thinkers.

Aristotle: God is the ultimate object of wonder, the Thought-Thinking-Itself
whose beauty moves the universe.

Christian, Jewish and Moslem: God is the Creator and Savior whom men
should adore.
Descartes needs God, not to save him or to adore, but simply so that he can know
ordinary facts about the world. He has, in a way, inverted the usual philosophical order, which
starts with experience and reasons to the existence of a God. He has to start with a God in
order to know anything about the world.
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