PHIL
111: Introduction to Philosophy
LARKIN:
Spring 2003
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Descartes,
Meditation One
A.
Quest
for Certainty
1. Descartes has realized that
he has some bad beliefs.
2. This raises suspicion about
whole belief system—if some are bad, then others might be too, plus many
beliefs have since been built on the bad ones.
3. Descartes wants a system
that does not have any false beliefs and where all the beliefs are
certain/guaranteed.
4. Foundationalism: Our belief
system is built on a foundation of basic beliefs, which can justify other
beliefs but are themselves not justified by other beliefs.
5. Certainty demands finding
basic beliefs that are absolutely certain and connections between beliefs that
preserve that certainty.
B.
Method
of Universal Doubt
1. Descartes wants to knock
down his entire old system of beliefs.
2. So he wants to generate
doubt about all of his previous beliefs, or as many as possible.
3. Descartes wants to find
certain foundations on which to build a new system of beliefs.
4. So he wants to actively try
to doubt everything in order to find something that he cannot doubt—something
that is indubitable and therefore certain.
5. Thus Descartes embarks on a
process of trying to doubt as many beliefs as possible by formulating skeptical
arguments.
1. The argument
P1: My
senses sometimes deceive me.
P2: One
should never completely trust what once has deceived one.
C1: So I
should not completely trust my senses.
P3: All of
my beliefs have come either from or through my senses.
C2: So I
should not completely trust any of my beliefs.
2. Problem: The argument is self-defeating
If the conclusion is true, then the first premise is
undermined. For we cannot know that our
senses sometimes deceive us unless we at some point trust our senses to tell us
that our senses at some other point were mistaken.
3. Works for:
The argument succeeds in generating doubt about
empirical propositions concerning ‘extreme’ circumstances—objects that are far
away, very small, dimly lit, etc.
4. But not for:
The argument does not generate doubt concerning
propositions about matters ‘close at hand’.
Our senses do sometimes deceive us, but not about matters in ordinary
closes-at-hand circumstances.
1. The argument
P1: If I
really know that P, then I can rule out the possibility that I am merely
dreaming that P.
[If I cannot tell whether I am dreaming, then I
cannot really tell whether there is a table in front of me. If I was merely dreaming the table, then
there (probably) would not really be a table in front of me.]
P2: But I
cannot rule out the possibility that I am merely dreaming that P.
[There does not seem to be any test that I can
perform that I can use to definitively determine whether I am dreaming or
not. For any test we come up with, it
seems we can dream that we perform it and dream that we get whatever results.]
C: So I do not really know that P.
2. Argument Form
a.
The
argument form exemplified here is called modus tollens or denying the
consequent.
P1: If P,
then Q.
P2: Not-Q.
C: So Not-P.
b.
Denying
the Consequent is valid: It is
impossible for the premises to be true but the conclusion false.
c.
So
if the conclusion is false, at least one of the premises must be false.
d.
This
form should be carefully distinguished from the following, called denying
the antecedent:
P1: If P,
then Q.
P2: Not-P.
C: So,
Not-Q.
e.
Denying
the Antecedent is Invalid.
f.
It
is possible for the premises to be true but the conclusion false:
P1: If Lassie
is a dolphin, then she is a mammal.
P2: Lassie
is not a dolphin.
C: So Lassie
is not a mammal.
3. Works for:
The Dream Argument is sufficient to generate doubt
for propositions about complex objects—like tables and chairs and bodies and
such—the kinds of things studied by Physics, Astronomy, and Medicine.
4. But not for:
The Dream Argument is not sufficient however to
generate doubt for propositions about simple objects—like colors, shapes,
quantities, space, time—the kinds of objects studied by Arithmetic and
Geometry.
1. The Argument
P1: If I
really know that P, then I can rule out the possibility that there is an
all-powerful evil genius deceiving me about P.
P2: But I
cannot rule out the possibility that there is an evil genius deceiving me.
C: So I do not really know that P.
2. Works for:
The Evil Genius argument is the best possible
skeptical argument—the evil genius is all-powerful and so can generate doubt
about anything for which it is possible to generate doubt about. The argument works for propositions about
complex objects as well as propositions about simple objects.
3. But not for:
Still the Evil Genius argument cannot generate doubt
about my own existence or the fact that I am thinking. Not even an all-powerful evil genius can
make me think that I exist when I do not exist. This would require making me exist and not
exist at the same time, which is impossible.
And not even an all-powerful evil genius can make me think that I
am thinking when I am not thinking.
This would require making me think and not think at the same time, which
is impossible.