Meditations on First Philosophy
(Text, pp. 87-119)
The problem of skepticism (D concentrates
on 2 types of skepticism)
– General skepticism: There are NO indubitable
beliefs or propositions.
– Skepticism concerning the existence & nature
of the “external world”: The existence and
nature of the “external world” cannot be
The overall structure of D’s
General Cogito (existence of the “I”)
(Med. I) (Med. II)
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)
Radical (General) Skepticism
(Text, pp. 87-92)
Epistemological Foundations & Superstructure
False False False
Foundational Foundational Foundational
Belief Belief Belief
(See Text, 87-8)
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.
Empiricism: True beliefs are acquired through
sense experience (89).
My beliefs are not products of insanity (89).
My beliefs are not products of my dreams (89-90).
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) (90-91).
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) (91).
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
Descartes’ Refutation of Radical Skepticism
(Text, pp. 93-97)
Descartes’ refutation of
“Cogito ergo sum!”
What does this mean?
The most famous statement in
the history of philosophy:
“I think; therefore I am.”
Discourse on Method (1637)
“If I am deceived,
then I must exist!”
I cannot doubt the truth of
the statement, “I exist.”
Radical (general) skepticism is refuted.
Meditation II, cont’d
The Mind-Body Problem &
Descartes’ Psycho-Somatic Dualism
perspectives relevant to the
Metaphysical Dualism: Reality is two-
dimensional, partly material and partly non-
material (minds, ideas, souls, spirits,
Metaphysical Materialism: Reality is nothing
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?).
Application to the “mind-body problem”
Metaphysical Materialism: A person is nothing
but a physical organism (body only).
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, soul, spirit) and
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.
Is Descartes right?
Can you doubt the existence
of your body (as well as
other physical things)?
Why or why not?
“I can conceive of myself as
existing without a body, but
I cannot conceive of myself
as existing without
Bryan Magee, The Great
Philosophers (Oxford 1987)
In Descartes’ view,
my body exists (if it exists at all)
outside of my consciousness and is
therefore part of the “external world.”
Descartes’ mind-body dualism
leads to . . . .
which deals with
(1) skepticism concerning the
existence & nature of the
(2) the existence of God
(Text, pp. 97-110)
“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” (Text, 99).
Why does Descartes say this?
Descartes’ standard of
What does it take for a belief to be
certainly (indubitably) true?
The belief must be “clear and
Descartes’ general rule: “Everything
that I can clearly and distinctly grasp
Are the following beliefs
“clear & distinct”
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 ?
Reasons for believing (1) that there
are things outside myself (2) which
cause my ideas of those things in my
mind and (3) that my ideas of
external things “resemble”
(accurately represent) the things
*The epistemology represented by
(1), (2), & (3) is known as
“Common Sense Realism” or
•I have a strong natural inclination to
believe these things.
•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
(Do these reasons “clearly &
distinctly” prove that Common
Sense Realism is true?) (See 100)
Ideas & their causes
When I think of an entity, I can
distinguish between . . . .
Substance (i.e., the entity itself, e.g., an
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
And isn’t it obvious that substance
(Text, 101) is more real than mode or accident?
Ideas of things (substances,
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.
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
to be in the mind (102). fender &, from my
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
(anything greater or more car as NOT having a
perfect) than is in the things dented fender?
the ideas represent (102-3). How might Descartes
respond to this criticism?
If one of my ideas
has something in it that is not within myself,
I could not be the cause of that idea;
if I could be the cause of all of my ideas,
I will have no foolproof reason to believe
that anything exists other than myself.
Ideas in my mind:
of myself (could be caused by myself)
of lifeless physical objects
Could be composed from my
of animals ideas of myself, physical
objects, and God (how?)
of other people
What about physical objects?
The qualities of physical objects:
Primary qualities: size, length,
breadth, depth, shape, position, motion,
substance, duration, number, etc.
Secondaryqualities: light, color,
sound, odor, taste, heat, cold, etc.
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.
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
But what about my ideas of extension, shape,
position, and motion?
Although extension, shape,
position, or motion do not exist
in me (since “I” am not a
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.
I could be the cause of my
ideas of both the primary and
of physical objects.
I do not have what it takes
to produce the idea of God
(an infinite substance)
from within myself
(a finite substance).
Descartes’ first argument
for the existence of God . . . .
“By ‘God,’ I mean
an infinite and independent
SUBSTANCE, all-knowing and all-
powerful, who created me and
everything else . . . . ” (Text, 105)
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 . . . .
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!
Descartes’ main point here is
that I could not be the How could I, merely
cause of the idea of from within myself,
God that I find in my form the idea of a
mind being more perfect
since God is a being than myself?
more perfect than Then my idea would
myself. represent more reality
than there is in its
Only God is a sufficient cause
of the idea of God in my mind.
Descartes’ second argument
for the existence of God . . . .
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 -- which means
that I must be caused to exist (at
every moment of my existence) by
something other than myself (108-9).
If the cause of my existence
is itself a contingent being (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
(See Text, 109)
I could never begin to exist.
So . . . .
there must be a First Cause
whose existence is necessary (rather
Furthermore . . . ,
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,
that this First Cause must be God (since
only God can be the original cause of the
idea of God in any mind).
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?
(See Text, 109-110)
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] . . . .
The idea that God cannot
be a deceiver
(See Text, 111)
God & the removal of doubt as to
the existence of the external world
The content of Meditation V
Mathematical thinking & its (physical &
non-physical) objects: clarity &
distinctness again -- what is clear & distinct
must be true (112-113)
D’s “ontological” argument for the
existence of God (115-116)
God & certainty (116-118)
Descartes’ third argument
for the existence of God
(the ontological argument again)
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.
Certainty about God
is the basis of certainty about
(See Text, 116-117)
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.
(See Text, 118-119)