Transcript Document 7330944

Lecture 2
(Think, pp. 14 – 34)
Descartes and the Problem of
Knowledge:
I.
Some historical and
intellectual background
II.
What is knowledge?
III. Descartes’ Meditations
IV. Some puzzles and problems
(Friday class)
I. Some historical and
intellectual background:
Biographical Information about Descartes:
Born 1596 – Died 1650
Educated by Jesuits in the dominant Scholastic
intellectual tradition
As mathematician, scientist and philosopher, he
was central figure in Scientific Revolution of 17th
Century
The Scholastic Tradition:
Derived from writings of Aristotle (384-322 BC)
Aristotelian Science – Tried to explain natural
phenomena by appeal to 4 types of causes:
Material Cause (what a thing is made of) “The ball
bounced because it’s rubber.”
Formal Cause (How a thing is structured) “The ball
rolled because it’s spherical.”
Efficient Causes (What brings something about) “The
ball rolled because it was pushed.”
Formal Causes (What a thing’s purpose is) “The ball
rolled because that’s what balls were designed to do.”
Descartes and some contemporaries (Galileo)
try to develop new approach to scientific
understanding
Rejected “teleological explanations” (Aristotle’s
Final Cause)
Try to explain world by appeal to laws,
mechanical principles, and mathematics
Argued that all matter was the same throughout
the universe
This was VERY controversial, since it was
inconsistent with religious orthodoxy
Descartes’ intellectual goal was to build a new
and solid foundation for knowledge
Was an enormously grand conception or plan
Also, it was relatively dangerous (considering
the period)
Descartes’ most famous work was entitled
Meditations on First Philosophy In Which The
Existence of God and the Distinction of the Soul from
the Body Are Demonstrated (1641)
A series of 6 “meditations” in which Descartes
tries to establish what it is, if anything, he can
know for certain
II. What IS knowledge?:
Epistemology is the study of knowledge
What do we mean by the word “knowledge”?
When would we say that someone knows some
proposition p?
They must believe p.
P must be true.
They must be justified in believing that p.
Thus, knowledge is (at a minimum) justified, true
belief.
These are necessary conditions for knowledge.
Are they sufficient? (Gettier-type examples)
III. Descartes’ Meditations
The project:
To clear away all false or doubtful beliefs
To establish a solid foundation on which he can build
explanations about the world
The project involves what epistemologists call “a
foundationalist” view about knowledge
Starting point is to determine which beliefs of his are
or might be false
To this extent, Descartes begins with a strong sceptical
position about knowledge
There are at least two methods that Descartes
might have followed:
He might have examined each one of his beliefs
in turn, and reject those that are false or
doubtful
He might examine the commonsense principles
which he has used to acquire beliefs about the
world, and reject those that are not reliable
The first method is far to cumbersome
Descartes chose the second method
First Principle (of commonsense):
(P1) The senses (sight, touch, smell,…) are our most
reliable means of acquiring true beliefs about the
world.

Descartes rejects (P1) and seems to offer the
following as an argument(1) Our senses sometimes deceive us (e.g. when the
lighting is poor, or there are other “problems with
the external circumstances).
Therefore,
(C) We should never trust our senses. (i.e. we should
reject (P1))
But perhaps we can improve on (P1) as follows:
(P2) When the external conditions are ideal, our senses
are our most reliable means of acquiring true beliefs
about the world.
But Descartes notes some problems associated with this
principle
People who are delusional or insane often have
hallucinations – their senses are not reliable sources of
knowledge even when the external conditions are perfect
When he dreams, Descartes often misbelieves that what
he is aware of is actually happening
Descartes argues that he has no way of being certain
that he is sane or that he is not dreaming
So, Descartes is convinced that unless he can be
sure that the external and internal conditions
are right, he should not trust his senses as a
source of knowledge.
He feels that he has no way to determine when
the external and internal conditions are correct
So, he feels he should not use his senses as a
guide to knowing about the world
Having convinced himself that the basic principles of
commonsense (i.e. (P1) and (P2)) are false, Descartes
then introduces one of his most famous pieces of
reasoning, The Evil Demon Argument:
(1) It is possible that there is an Evil Demon who
systematically deceives me.
(2) Unless I can be sure that there is no such Evil
Demon, I should doubt ALL of my beliefs.
(3) But I cannot be sure that there is no such Evil
Demon.
(4) Therefore, I should doubt ALL of my beliefs (i.e. I
should be a sceptic)
Descartes’ Predicament:
By the end of Meditation One, he finds he is able
to doubt everything .
This leaves him with basically nothing on which
to construct new, more certain, beliefs.
He begins Meditation Two by reflecting again on
what he thought he knew.
What he discovers is something quite
remarkable…
“I think, therefore I am!”
This is known as Descartes’ Cogito
“Cogito ergo sum”
Essentially, what he discovers is that there is, as a matter
of fact, one belief that he CANNOT doubt
i.e. one belief of his that must be true
Even the hypothesis of an Evil Demon will not cast
doubt on the fact that insofar as he thinks, or doubts, he
MUST exist.
(Friday’s class – Some Problems and Puzzles raised by
these arguments)
iv. Some puzzles and problems
(Friday class)
Is justified, true belief sufficient for knowledge?
What is this self about whose existence
Descartes is so certain? What kind of thing is it?
How does he come to know it?
Does Descartes’ argument presuppose that some
of our sense perceptions are true or “veridical”
Is justified, true belief sufficient for knowledge?
Some offer counter-examples in an attempt to show
that these conditions are not sufficient (Gettier-type
counter-example): Suppose that
1. Smith and Jones are candidates for the same job
2. Smith believes, with good reason, that Jones is better
qualified
3. Smith knows that Jones has 12 stones in his pocket
4. Smith comes to believe, because of 2 & 3, that the
person who will get the job has 12 stones in his pocket
5. Smith ends up getting the job
6. Unbeknownst to Smith, he also had 12 stones in his
pocket
Question: Did Smith know that the person who will get
the job has 12 stones in his pocket
What is this self about whose existence Descartes is so
certain? What kind of thing is it? How does he come to
know it?:
A thinking thing (res cogitans)
Not extended, not material, a thinking substance (not a
material substance)
Knowledge of the self is not dependent on his knowing
anything about bodies/(matter) that exist(s)
Descartes can doubt whether he has a body
He cannot doubt that he exists
Therefore,
What justifies his belief that he exists is
independent of material things
The point of Descartes’ discussion about piece of wax
is supposed to show that bodies, like his mind, are
also perceived by the intellect (not the senses)
 Descartes’ argument for the distinctness of mind and
matter would be flawed if it were the following:
1) I can doubt whether I have a body.
2) I cannot doubt that I exist.
Therefore,
3) I am ≠ my body
 This would be an instance of The Masked Man Fallacy
Compare:
1) I doubt whether Samuel Clemens was American.
2) I don’t doubt that Mark Twain was American.
Therefore,
3) Samuel Clemens ≠ Mark Twain





Does Descartes’ sceptical argument
presuppose that some of our sense perceptions
are true or “veridical”?
When he says that he knows some of his
perceptions have been false/misleading, this
might suggest that he knows that other
perceptions are true or veridical.
But this is not the only (or most charitable)
way to understand his argument.
He may be appealing to the fact that in the past
his beliefs based on sensory evidence have
been inconsistent
he would, thus, know that not all of them
could be true (but all could be false).

Next class – Read the rest of Chapter 1
- Re-read the first half of Chapter 1

Lecture notes WILL be posted on course web
page
www.ryerson.ca/~ahunter/PHL201/