Descartes provides a summary of his meditations on philosophy and skepticism. He introduces radical skepticism and uses the "cogito ergo sum" argument to refute it, establishing his own existence as certain. He then explores mind-body dualism and the possibility that the external world is an illusion. Descartes argues that proving God's existence would guarantee that the external world is real, so he provides an ontological argument that the idea of a perfect God must have been caused by God's actual existence.
3. Revised, 1/7/07
René Descartes
(1596-1650 AD)
Meditations on First Philosophy
(1641)
4. Background
Descartes’ Problem
The problem of skepticism (D concentrates on 2
types of skepticism)
– General skepticism: There are NO indubitable (not
doubtable) beliefs or propositions.
– Skepticism concerning the existence & nature of the
“external world”: The existence and nature of the
“external world” cannot be known.
– The Matrix: http://www.youtube.com/watch?v
=lEr8hnvzeHU
6. General Cogito (existence of the “I”)
(Med. I) (Med. II)
Mind-Body Dualism
(That piece of wax)
Skepticism
God (no deceiver)
External 1. My idea of God (III)
World 2. My contingent
(Meds. III-VI) existence (III)
3. The ontological
argument (again) (V)
8. Descartes’ “Foundationalism”
Epistemological Foundations & Superstructure
Superstructural
Beliefs
(also false?)
False False False
Foundational Foundational Foundational
Belief Belief Belief
If the underlying foundations of our beliefs are false, then it is
possible that all of our beliefs are false too!
9. D’s program of radical doubt
Treat any belief that is to the slightest
extent uncertain & subject to doubt just as
though it is obviously false.
Accept only those beliefs that are
completely certain and indubitable.
Work on the foundations of my beliefs.
What are the underlying foundations of my beliefs?
10. Foundational Beliefs
(common assumptions we make)
Naïve Empiricism: True beliefs are acquired
through sense experience.
My beliefs are not products of insanity.
My beliefs are not products of my dreams.
11. Foundational Beliefs, cont’d
Physical objects: Even if we fail to
perceive physical objects accurately, the
“primary [measurable] qualities” of such
objects (matter, extension, shape, quantity,
size, location, time, etc.) are really real
(i.e., physical objects do really exist).
Even if empirical beliefs are subject to
doubt, mathematical propositions are
indubitable (e.g., 3 + 2 = 5, a square has
neither more nor less than four sides).
12. How does Descartes challenge each of the
foregoing foundational beliefs?
How does he use the ideas of God and the
Devil in building his case in support of
radical skepticism?
15. The most famous statement in
the history of philosophy:
“I think; therefore I am.”
Discourse on Method (1637)
16. “If I am deceived,
then I must exist!”
I cannot doubt the truth of
the statement, “I exist.”
I can't think that I am not thinking
because then I am thinking; and if I
am thinking, then I must exist. To
doubt my own existence, I must
exist!
20. Metaphysical Dualism: Reality is two-
dimensional, partly material and partly non-
material (minds, ideas, souls, spirits,
consciousness, etc.).
Metaphysical Materialism: Reality is nothing
but matter-in-motion-in-space-and-in-time.
There are no non-material realities.
Metaphysical Idealism: Reality is nothing
but Mind, Idea, Soul, Spirit, Consciousness,
etc. Matter does not exist (it’s an illusion?).
21. Application to the “mind-body problem”
Metaphysical Materialism: A person is nothing but a
physical organism (body only). "Mind" (consciousness)
a feature (function, epiphenomenon) of the body.
Metaphysical Idealism: A person is “consciousness
only” (mind, soul, spirit); not at all a material being.
Metaphysical Dualism: A person is a composite of (1)
“mind” (consciousness, intellect, soul, spirit) and (2)
body.
22. Cartesian Dualism
I know with certainty THAT “I” exist
(Cogito ergo sum), but
WHAT am “I”?
Am “I” my body? No, because I can doubt
the existence of my body, whereas I cannot
doubt the existence of myself (the “I”).
“I” am a thinking thing, a thing that doubts,
understands, affirms, denies, wills, refuses,
imagines, and has sensations.
23. Mind-body distinction
P1: My body has the property of being such that its existence can rationally be
doubted by me (evil demon hypothesis).
P2: my mind does not have the property of being such that its existence can
rationally be doubted by me (cogito sum)
P3 For any object A and B, if A=B then A and B have all of their properties in
common and there is no difference in their properties (Leibniz’ Law [naïve
form] or principle of the Indiscernibility of Identical)
C1: my body has a property that my mind does not have, namely the property
of being such that its existence can be rationally doubted by me (conjunction
P1,P2)
C2: my body is not equal to my mind (modus tollens, P3, C1).
–
Modus Tollens: Where means "P implies Q", means Q is false (not Q). The
modus tollens rule, then, is that wherever both " " and " " appear by
themselves on a line of a proof, then " " can validly be placed on a subsequent
line
24. Is Descartes right?
Can you doubt the existence
of your body (as well as
other physical things)?
Why or why not?
25. “I can conceive of myself as
existing without a body, but
I cannot conceive of myself
as existing without
conscious awareness.”
Bryan Magee, The Great
Philosophers (Oxford 1987)
26. Detour
Descartes' piece of wax
(What is this about?)
D' piece of wax is a physical object.
How is it known? Through the senses?
Through the power of imagination?
Through the intellect (judgment,
intuition)?
27. That piece of wax….
A major dispute running through the entire history of philosophy has to do with the
source(s) of human knowledge. There are two major schools: rationalism and
empiricism. The empiricists hold that knowledge is derived from sense perception
and experience. The rationalists (such as Descartes) hold that knowledge is derived
from clear logical thinking, from the intellect (i.e., from "reason").
In the "wax" section, which is a kind of detour from his main argument, Descartes
is showing his support of rationalism. He argues that we know - through the
intellect - that the wax is and remains what it is as it passes through time and
change. Sense perception does not show the "substance" of the wax but only its
various appearances. If we relied on sense experience rather than on "reason,"
then we would "know" that the wax is all of the following: cold and hard, warm
and soft, hot and liquid. However, "reason" (not the senses) tells us that the
substance (reality) of the wax is something more fundamental than its sensual
appearances.
Process Philosophy notes that identity can remain through change
28. Back to the mind-body problem….
So…
in Descartes’ view,
my body exists (if it exists at all)
outside of my consciousness and is
therefore part of the “external world.”
Thus,
30. Meditation III,
which deals with
(1) skepticism concerning the
existence & nature of the
“external world”
&
(2) the existence of God
Brain in a vat: http://
www.youtube.com/watch?v
31. “I must, as soon as possible, try to
determine (1) whether or not God
exists and (2) whether or not He
can be a deceiver. Until I know
these two things, I will never be
certain of anything else”
Why does Descartes say this?
32. And why does Descartes think it
necessary to prove the existence of God?
It's because he's looking for a guarantee that the "external world"
(the world outside of his mind) is really real and not just an
illusion. How does a proof of the existence of God help him with
that problem?
The point is that God (who is no deceiver) guarantees that the
world I perceive through my senses is really there. God
authenticates my sensory experiences, thus making sensation
generally reliable, not in and of itself, but because God (being
perfectly good) will not allow me to be systematically deluded and
deceived.
By the way, if Descartes trusted his senses, this "external world"
issue would not be a problem for him. But Descartes, a
"Rationalist" rather than an "Empiricist," does not trust sense
experience. He needs something more than sense experience to
convince him that the "external world" is real. He needs God.
33. Descartes’ standard of
certainty
What does it take for a belief to be
certainly (indubitably) true?
The belief must be “clear and
distinct.” (But what does this mean?)
Descartes’ general rule: “Everything
that I can clearly and distinctly grasp
is true.”
34. Are the following beliefs
“clear & distinct”
(indubitable)?
That there are things outside myself (such
as physical objects).
That these external things cause my ideas of
those things in my mind.
That my ideas of external things perfectly
“resemble” the things themselves.
That 3 + 2 = 5 ?
35. Reasons for believing (1) that there
are things outside myself, (2) that
these external things cause my ideas
of those things in my mind, and (3)
that my ideas of external things
“resemble” (accurately represent) the
things themselves*:
*The epistemology represented by
(1), (2), & (3) is known as
“Representationalism.”
36. I have a strong natural inclination to
believe the preceding three
propositions.
My ideas of external things arise in
my mind independently of my will.
It seems obvious that external
objects impress their own likenesses
upon my senses.
(Do these reasons “clearly & distinctly” prove that
Representational Realism is true?)
38. When I think of an entity, I can
distinguish between . . . .
Substance (i.e., the entity itself, e.g., an
automobile tire),
Modes (i.e., the ways in which the entity exists,
e.g., the tire may be flat ), and
Accidents (i.e., the properties, qualities, or
attributes of the entity, e.g., the color of the tire
[blackness?] ).
And isn’t it obvious that substance
is more real than mode or accident?
39. Ideas of things (substances,
modes, accidents)
must be caused to be in the mind, and
the cause of any effect must be sufficient
to produce its effect, i.e.,
there must be at least as much reality in a
cause as is represented in its effect.
40. Descartes thinks of ideas as
But is this last point true?
subjective representations of Suppose I perceive an
the realities that cause them automobile with a dented
fender &, from my
to be in the mind. perception, an idea of the
He also believes that ideas car arises in my mind.
cannot represent more reality Why can’t I think of the
car as NOT having a
(anything greater or more dented fender?
perfect) than is in the things How might Descartes
the ideas represent. respond to this criticism?
41. If one of my ideas
has something in it that is not within
myself, then
I could not be the cause of that idea;
whereas
if I could be the cause of all of my ideas,
then
I will have no foolproof reason to believe
that anything exists other than myself.
42. Ideas in my mind:
of myself (could be caused by myself)
of God
of lifeless physical objects
of angels
Could be composed from my
of animals ideas of myself, physical
objects, and God (how?)
of other people
What about physical objects?
43. The qualities of physical objects:
Primary qualities: size, length,
breadth, depth, shape, position, motion,
substance, duration, number, etc.
Secondary qualities: light, color,
sound, odor, taste, heat, cold, etc.
44. Since my ideas of the secondary
qualities of physical objects
are not “clear and distinct,”
and since such qualities are almost
indistinguishable from nothing (i.e, they
seem to represent very little reality),
I myself [a substance] could be the author
of such ideas.
45. I could also be the cause of
my ideas of primary qualities.
I am a substance.
I have duration in that I exist now and have
existed for some time.
I can count my several thoughts and thus the
idea of number may be grounded in my thought
process.
But what about my ideas of extension, shape,
position, and motion?
46. Although extension, shape,
position, or motion do not exist
in me (since “I” am not a
physical being),
these are only modes of
existence, and, as a substance,
“I” have more reality than these
modes and “I” am therefore
sufficient to cause my ideas of them.
47. Thus,
I could be the cause of my
ideas of both the primary and
secondary qualities
of physical objects.
However,
48. I do not have what it takes
to produce the idea of God
(an infinite substance)
from within myself
(a finite substance).
50. “By ‘God,’ I mean
an infinite and independent
SUBSTANCE, all-knowing and all-
powerful, who created me and
everything else . . . . ”
This idea represents more reality than there is
in myself (since I am finite, limited in
knowledge & power, etc.). Thus, the idea of
God must be caused to be in my mind by
something other than myself. And . . . .
51. since there must be at least
as much reality in a cause as
there is in its effect(s),
it follows “necessarily” that my idea of God
must be caused by God Himself; and if God is
the cause of my idea of God, then
God must exist!
52. Descartes’ main point here is
that I could not be the How could I, merely from
cause of the idea of God within myself, form the
that I find in my mind idea of a being more
since God is a being more perfect than myself?
perfect than myself. In that case, my idea
Anselm’s Ontological would represent more
Argument reality than there is in its
cause.
Only God is a sufficient cause
of the idea of God in my mind.
53. "Step 3" Presentation of D's 1st Argument
for the Existence of God
(not sure about this)
1. All events are caused.
2. A cause must be sufficient to produce its effects.
3. My idea of a perfect being is a mental event.
4. Only a perfect being is a sufficient cause of my idea of a
Perfect being.
5. If a perfect being is the cause of my idea of a perfect being,
then a perfect being exists.
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6. A perfect being (God) exists.
55. I exist as a thinking thing
with the idea of God (an infinitely
perfect being) in my mind,
but my existence is not necessary -- it is
contingent (i.e., my non-existence is conceivable,
logically possible) -- which means
that I must be caused to exist (at
every moment of my existence) by
something other than myself.
56. If the cause of my existence
is itself a contingent being or a set of contingent
beings (e.g., my parents or something else less
perfect than God), then
it must also be caused to exist by something other
than itself. But . . . .
this cause-and-effect process cannot go on to infinity
since in that case
I could never begin to exist (the infinite regress
problem again).
So . . . .
57. there must be a First Cause
whose existence is necessary (rather
than contingent).
Furthermore . . . ,
58. this necessarily existing First Cause,
which is the ultimate cause of my existence,
must have the idea of God in it, and
since it is a First Cause, its idea of God
must be caused by itself and nothing else,
which means
that this First Cause must be God (since
only God can be the original cause of the
idea of God in any mind). – (remember
Aquinas?)
59. "Step 3" Presentation of D's 2d Argument
for the Existence of God
(not sure about this)
1. All contingent beings must be caused to exist.
2. I exist as a contingent and thinking being, with the idea of a perfect being in my
mind [and as contingent, I must be caused to exist--premise 1].
3. If something causes existence only if it is itself caused to exist, then its causal
series is infinitely long.
4. An infinite (or infinitely regressing) series of causes leading up to my present
existence is logically impossible, since, in that case, I could never begin to exist
[i.e., I would have no existence at all].
5. A cause must be sufficient to produce its effects.
6. To be a sufficient cause of my existence, the "first cause" of my existence must
be a necessarily existing [premises 4 and 5] and thinking being possessing the
idea of perfection [premise 2].
7. The "first cause" of my existence is the cause of its own idea of perfection and is
therefore, itself, a perfect being [otherwise it would not be "first"].
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8. A perfect being (God) exists.
60. Why does Descartes reject
the claim that
his existence as a contingent being with the
idea of God in its mind might be the effect of
several natural causes, each representing a
different kind of perfection?
61. Conclusion of the 3rd Meditation
"From the simple fact that I exist and that I have in my
mind the idea of a supremely perfect being, that is,
God, it necessarily follows that God exists . . . . The
whole argument rests on my realization that it would
be impossible for me to exist as I do -- namely, with
the idea of God in my mind -- if God didn’t exist. It
also follows that [since God is perfect] God cannot be
a deceiver [because fraud and deception are caused by
defects] . . . ."
62. Summery
Archimedean point – find a foundational principle
Cogito Ergo Sum – I think therefore I am
Descartes in 90 min: http://
www.youtube.com/watch?v=eTYkMOc3Yjc
Williams - http://www.youtube.com/watch?v
=44h9QuWcJYk
63. The idea that God cannot
be a deceiver
leads to
Slides on Meditation IV under construction – but see next slide for a brief summary….
64. The Basic Thrust of Meditation IV:
If God is no deceiver, how is human error with respect to truth and falsity possible,
and how is that error to be explained?
Human nature is equipped with an intellect (faculty of knowing) and a free will
(faculty of choosing), which interact in the pursuit of truth. The intellect is capable
of forming beliefs that can't be doubted and therefore are certainly true. However,
the intellect can also consider claims that are subject to doubt and that therefore
may be false. The human will is free to affirm or deny propositions proposed to it
by the intellect. Error results when the will (1) denies the truth, or (2) affirms
claims that are false, or (3) asserts knowledge where there is doubt.
Error is avoidable where a person limits her his affirmations and denials to "those
matters that are clearly and distinctly [indubitably] shown to . . . [the will] by the
intellect . . . . " and remains (more or less) neutral with respect to all claims that are
subject to doubt.
Why does God permit human error? If human nature were created both free and
incapable of error, it would be more perfect than it now is; but it may be that the
apparent imperfection of human nature in this respect is necessary to "a greater
perfection of the universe as a whole."
65. God & the removal of doubt as to
the existence of the external world
66. The content of Meditation V
Mathematical thinking & its (physical &
non-physical) objects: clarity &
distinctness again -- what is clear & distinct
must be true
D’s “ontological” argument for the
existence of God
God & certainty
68. 1. If the nonexistence of God (an infinitely perfect
being) were possible, then existence would not be
part of God’s essence (that is, existence would not
be a property of the divine nature).
2. If existence were not part of God’s essence (that is,
a property of the divine nature), then God would be
a contingent (rather than necessary) being.
3. The idea of God as a contingent being (that is, the
idea of an infinitely perfect being with contingent
rather than necessary existence) is self-contradictory.
4. It is impossible to think of God as not existing.
5. The nonexistence of God is impossible.
70. Meditation VI
Removal of doubt as to the
existence of the external world
Since God exists
& is no deceiver,
it follows necessarily
that the external world can be
known to exist.
71. To be continued….
(There's a lot more in the 6th Meditation than is
covered in this presentation…so far.)
