Introduction to Philosophy
Lecture 9
Epistemology #2:
Descartes
By David Kelsey
The Copernican Revolution
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The Copernican Revolution:
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Begun by Copernicus (1473-1543). Published De Revolutionibus in 1543.
Prior to Copernicus, Ptolemy’s theory was dominant. It held that the Earth was the
center of a multisphere universe.
Copernicus takes a mathematical approach to interpreting the movements in the
heavens.
Heliocentric view…
Retrograde motion…
Kepler
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Johannes Kepler
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1571-1630
Makes advancements on Copernicus’ views
Tycho Brahe…
Gives a mathematical account of the heavens that is sun centered and which matches
observed data.
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Kepler’s 3 laws:
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1. The path of the planets is an ellipse, with the sun at one of the 2 foci that define it.
2. The areas swept out by a line from the sun to the planet are always equal in equal intervals
of time.
3. The square of the orbital period of a planet is directly proportional to the cube of the semimajor axis of its orbit.
Galileo Galilei
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Galileo Galilei:
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1564-1642
The telescope…
Gives us a mathematical theory of motion…
Implications of the
Copernican Revolution
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Implications of the Copernican Revolution:
– The universe is thought of as infinitely extended in space so it has no center
– The heavens aren’t eternal, immutable and divine
– The universe is thought of in purely quantitative terms, as a set of objects
that interact according to fixed mechanical laws.
– Questions persist?
The Church’s response to Galileo
& the Copernican Revolution
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The Church’s response to Galileo & the Copernican Revolution:
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In 1616: Galileo ordered by the court to not defend the Heliocentric view
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In 1632 Galileo publishes Dialogue Concerning the Two Chief World Systems
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In 1633 Galileo was was found guilty of holding and defending the heliocentric view.
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In 1633 the Church prohibits any teachings or holdings of the heliocentric view
Descartes
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Rene Descartes:
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lived from 1596-1650.
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Was an important mathematician, physicist and philosopher.
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Considered to be the father of modern philosophy
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His Meditations are one of the most influential works in all of philosophy.
Descartes response to Galileo
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Descartes response to Galileo:
– In November of 1619 he has a vision in a dream. This vision is of analytic
geometry.
• Descartes realizes that there is a isomorphism between geometry and algebra…
– In 1633 Descartes is set to publish his mathematical treatment of nature,
called a Treatise on the World, when he hears of Galileo’s condemnation.
• Postponing publication…
– Descartes then becomes interested in epistemology because he is afraid of
being persecuted for his scientific views.
• He thought that if he could show that his views were justified, then he wouldn’t be
in danger.
• So he tries to make up the most powerful skeptical arguments he can, and then
he goes about trying to refute them.
Skepticism
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Skepticism:
– Is motivated by:
• the fact that things may not appear as they really are and that the true nature of
things is indeterminable
– The senses can deceive us..
– The sense organs of animals differ from species to species
– Human preferences vary from individual to individual
• So we must suspend judgment
– We neither affirm nor deny any belief about the real nature of an object
The Skeptical Problem of the Criterion
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The Skeptical Problem of the Criterion:
– The central question: by what mark or criterion or standard are we to decide
which of our beliefs are true, and which knowledge.
• The skeptics answer:
– The argument:
• Any claim that some principle is a criterion for truth must be supported.
• But we shall need a 2nd criterion to decide if the support is sufficient.
• But then how do we support our use of this 2nd criterion? By means of some
further 3rd criterion. But then we must justify our use of this 3rd criterion by
means of a 4th.
• But then we find ourselves in an infinite regress. Or we find ourselves in a vicious
circle…
• See page 214 of Melchert…
– So we must suspend judgment.
Refuting the skeptic
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So a skeptic is someone who denies that we know anything.
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The skeptic doesn’t deny that we believe many things that may well be true.
Rather, they deny that our beliefs are ever justified.
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The problem of the criterion…
An Epistemological project: refute the skeptic
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In Epistemology, we study the arguments that skeptics give for their view.
This way we can refute their arguments.
By refuting the skeptic we can learn a lot about what it takes for a belief to be justified.
Descartes method of refuting the skeptic
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So Descartes aims at refuting the skeptic:
– Before we get to his refutation let’s talk about how Descartes practices
philosophy.
• Remember that Descartes wants to refute the skeptic to show his scientific views
can really be justified.
• So Descartes approach is a cautions one
• what previous philosophers lacked is a method…
– The Method:
• 1. Never accept anything as true if I don’t have evident knowledge of its truth;
accept only those beliefs that are so clear and distinct that you have no occasion
to doubt them
– Clear and Distinct…
• 2. Divide complex difficulties into simpler parts
• 3. Attempts at knowledge should proceed from simplest to complex
• 4. To make enumerations complete and reviews so comprehensive that he could
be sure to leave nothing out.
Descartes
method of doubt
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Descartes project: refute the skeptic
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Descartes tries to make up the most powerful skeptical arguments he can, and then he
goes about trying to refute them.
This is his Cartesian method of doubt.
Cartesian method of doubt:
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Early in the meditations Descartes uses two powerful skeptical arguments to show that
he can doubt any of his beliefs.
But by the end of his meditations he comes to realize you cannot doubt most things.
• His method of doubt is temporary.
• The reason for his doubting all his beliefs is to show he needn’t doubt any of
them!
• He is a skeptic just so that he can develop the most powerful arguments for his
position.
• But at the same time he develops the arguments in order to try and show them
unsound.
Two arguments for
skepticism
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The first Meditation:
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In the 1st meditation Descartes gives two very powerful skeptical arguments:
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The Skeptical arguments:
• The dream argument
• The evil demon argument
• Remember, he gives these arguments so that he can later refute them.
The Dream argument
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Skeptical Scenario:
– If you’re dreaming right now, you’re not in a philosophy lecture you’re at
home in bed.
– But, for all you can tell, you might be dreaming that you’re in a lecture.
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The argument:
– 1. If I don’t know that I’m not dreaming, then I don’t know that I’m in a
lecture.
– 2. I don’t know that I’m not dreaming.
– 3. Thus, I don’t know that I’m in a lecture.
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Notice that this argument tries to show that you don’t know that
you’re in a philosophy lecture right now.
– But, of course, it can be used to cast doubt on lots of other beliefs.
The Dream Argument
Premise 1
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1. If I don’t know that I’m not dreaming, then I don’t know that I’m
in a lecture.
– Skeptical scenario:
• The dream argument involves a skeptical scenario:
– Skeptical scenario: a situation in which all your evidence is as it actually is,
but your beliefs turn out to be false.
• The skeptical scenario presented here:
– You are at home in bed dreaming.
– Is incompatible with something you take yourself to know…
– if you knew that you were in a philosophy lecture…
The Dream argument:
premise 2
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2. I don’t know that I’m not dreaming.
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When you are dreaming, you have experiences that seem indistinguishable from the
veridical experiences you have when you are waking.
People also often believe they are awake when they are in fact dreaming.
Some questions:
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Are dream experiences indistinguishable from waking ones?
Is there any knowledge that can’t be called into question this way?
The evil demon
argument
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The Evil Demon:
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Suppose there were an evil demon who is causing you to vividly hallucinate all your
experiences.
The evil demon could also cause you to have false beliefs, and to mistake invalid
arguments for valid ones.
The Argument:
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1. If I don’t know that I’m not a victim of an evil demon, then I don’t know that I’m in a
lecture.
2. I don’t know that I’m not a victim of an evil demon.
3. Thus, I don’t know that I’m in a lecture.
The evil demon #2
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The evil demon argument:
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is more powerful than the dream argument:
The evil demon can give you experiences as vivid and consistent as any veridical
experience.
The evil demon can deceive you even about things that aren’t to do with your
experiences.
• The laws of logic…
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Other skeptical scenarios not discussed by Descartes:
What’s the skeptic up to?
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Skeptical arguments:
– What is the aim of a skeptical argument anyway?
• The aim of a skeptical argument isn’t to show that the skeptical scenario is really
true.
• The aim of the skeptical argument is to cast doubt on what you know.
– The skeptic wants you to grant that the skeptical scenario is merely
possible.
• And if we can grant that the scenario is possible then we admit that there is much
we don’t know.
• So the skeptic says: “No-one knows anything, no-one is justified in any belief’.
How can we reply
to the skeptical arguments?
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Possible replies to the skeptic:
– We could embrace skepticism.
– We could deny premise 1 of the argument…
• Maybe knowledge doesn’t take complete lack of doubt…
– We could deny premise 2 of the argument with:
• Descartes Foundationalism:
– Descartes tries to show that there are some things even an evil demon can’t
deceive me about.
– He then concludes that because he can’t be deceived about these things,
there cannot be an evil demon.
Skepticism
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Becoming a skeptic:
– Some philosophers have reacted to the skeptical arguments by becoming
skeptics.
• But they face a pretty serious problem of getting around the world without
bumping into things.
– Often skeptics say: We need to ditch the concepts of knowledge and
justification altogether and replace them with something else:
– For example, ‘well-confirmed hypothesis useful in practice’.
– But they need to explain why this isn’t just another name for justification.
Denying premise 2
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To answer the skeptic by denying premise 2:
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we have to show how our beliefs are justified.
How are beliefs justified?
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Beliefs are sometimes justified by other beliefs.
• My neighbor is walking about…
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The justifying belief also has to be justified itself.
• My neighbor again…
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So where does this chain of justification end?
• For most, the chain ends in a basic belief.
– Non-basic beliefs are justified by other beliefs.
– Basic beliefs are justified some other way
Foundationalism
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Descartes was a Foundationalist.
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According to Foundationalists:
– Every justified belief is ultimately justified by basic beliefs.
– Thus, if you can find a way to show that the basic beliefs are skeptic-proof,
you can make all the rest of the beliefs skeptic proof as well.
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Foundationalists think that knowledge is like a building:
– At the bottom is the foundation-the basic beliefs…
– Built on them, the beliefs that directly justify others…
– And built on them, further beliefs still
Foundationalism:
refuting the skeptic
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The Foundationalist has to do three things to refute the skeptical
arguments:
– 1-Tell us which of our beliefs are basic and which are non-basic.
– 2-Show that the basic beliefs are beyond skeptical doubt.
– 3-Show how the non-basic beliefs are justified by the basic ones.
The Cogito
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The Cogito:
– Descartes thinks that even the evil demon couldn’t deceive him about
whether he (Descartes) exists.
• “If there is a deceiver…then surely I exist, since I am deceived”
– Descartes famous slogan:
• ‘I think, therefore I am’.
• In Latin, ‘Cogito ergo sum’.
The Cogito as a basic belief
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According to Descartes, ‘I exist’ is a basic belief.
– So ‘I exist’ is immune to doubt.
– Not even the evil demon could deceive Descartes about this belief.
Deception presupposes a Deceived
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Deception presupposes an I that is being deceived:
– As Descartes says: So let the evil demon deceive me about my thoughts
and in this case all of my thoughts are false. But if the evil demon can
deceive me then there must be an ‘I’ that is being deceived. Thus, this ‘I’
exists.
– So only ‘I exist’ is guaranteed true
• ‘Descartes exists’ isn’t so guaranteed.
– Descartes could be an illusion after all.
• But in believing ‘I exist’:
– the evil demon couldn’t’ deceive this ‘I’ that is thinking about whether this ‘I’
exists.
– For such deception presupposes an ‘I’ to be deceived.
Thought
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The truth of my existence is guaranteed by my engaging in
thought:
– Thought here includes: doubting, understanding, affirming, denying, willing,
unwilling, imagining, dreaming and reflecting.
– One deduces her own existence from her own thought.
– Examples…
The Cogito: self justifying
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The guarantee of truth:
– The truth of the belief ‘I exist’ is only guaranteed while you are thinking.
• I exist so long as I am thinking.
• “I am, I exist-that is certain. But for how long? For as long as I am
thinking. For it could be that were I totally to cease from thinking, I
should totally cease to exist.” (Meditation II)
The cogito as an argument
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The cogito is an argument:
– 1. I am thinking.
– 2. Thus, I exist.
– Even the skeptic has to recognize this argument as sound!!!
– It’s premise is true and it cannot be doubted for it is self justifying.
• You can know the cogito is true just by thinking on the cogito itself.
Objection 1:
Does anyone exist?
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Does anyone exist at all?
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Descartes is certain that he exists…
But it’s clear to me that Descartes could be an illusion created by an evil demon.
Meanwhile it seems to me to be certain that I exist, but to Descartes it is clear that I
could be an illusion.
Clearly, it isn’t certain that anyone exists at all.
Descartes reply:
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I didn’t say that ‘Descartes exists’ is skeptic proof.
It’s ‘I exist’ that’s skeptic proof.
Objection 2:
What’s special about the cogito?
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There’s nothing special about the cogito.
– It’s no more nor less sound than this argument:
• 1. I am walking.
• 2. Therefore, I exist.
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Descartes reply:
– ‘I am walking’ is not a self-justifying belief.
Objection 3:
Does thought require a thinker?
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Couldn’t the evil demon create the thought ‘I am thinking’ without creating
a thinker?
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Descartes reply:
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That’s absurd, you can’t have a thought without a thinker.
Counter to Descartes:
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But now isn’t Descartes using another belief, that you can’t have a thought without a
thinker, to justify the cogito?
Finishing Descartes program
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The Foundationalism project:
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Recall that the Foundationalist has to do three things:
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Tell us which of our beliefs are basic and which are non-basic
Show that the basic beliefs are beyond skeptical doubt.
Show how the non-basic beliefs are justified by the basic ones.
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We’ve just been looking very closely at Descartes’ attempt at the second part of
this.
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But what about the third part?
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How could the cogito justify other non-basic beliefs?
Descartes and
the justification of
non-basic beliefs
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Descartes would himself agree that the cogito alone is too narrow a basis for
the whole of our knowledge.
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In fact, Descartes thinks he has two basic beliefs:
– ‘I exist’
• He gets this from the cogito
– ‘God exists’
• He gets this from several arguments which we will now look at…
Solipsism
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Solipsism:
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Note that Descartes seems to also want to show that God exists to show that he is not
alone in the world. This is the view known as Solipsism.
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Solipsism is the view that for each person he can merely state “I am the only thing that actually
(formally) exists; everything else is only real for me.” (Melchert page 333)
“If I can be sure that the subjective reality of one of my ideas is so great that it isn’t in
me either formally or eminently and hence that I cannot be the cause of that idea, I can
infer that I am not alone in the world--that there exists something else that is the cause
of the idea. But if I can find no such idea in me, I will have no argument at all for the
existence of anything other than me…”(Med. III)
Descartes arguments for
God’s existence
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Descartes arguments for God’s existence:
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In the 3rd Meditation, Descartes gives 2 arguments for God’s existence. Here is the
first:
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1. I have an idea of an infinitely perfect substance.
2. Such an idea must have a cause.
3. Nothing comes from nothing
4. The cause of an idea must have at least as much formal reality as there is subjective reality
in the idea. (from 2 & 3)
5. I am a substance who is not infinitely perfect.
6. I could not be the cause of this idea. (from 1, 4 & 5)
7. So there must be a formal reality that is an infinitely perfect substance (from 1, 4 & 6)
8. So God exists (from 7)
Formal and subjective reality
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Descartes argument assumes the notions of formal and subjective reality:
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Premise 4 of Descartes argument makes use of the notions of formal and subjective
reality:
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Formal Reality:
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Something has formal reality if it actually exists.
When you form an image in your mind, the image has formal reality because it actually exists
as an image in your mind.
So an idea of an object represents the object and so both the idea and the object have formal
reality of their own.
Subjective Reality:
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When you entertain an idea your thoughts have subjective reality: reality for you.
Some objects have only subjective reality: the tooth fairy…
Evaluating Descartes first argument
for God’s existence
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Evaluating Descartes argument:
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Premise 1: I have an idea of an infinitely perfect substance.
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Premise 2: Such an idea must have a cause.
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This follows from the fact that nothing comes from nothing and something cannot come from
nothing.
Premise 4: The cause of an idea must have at least as much formal reality as there is
subjective reality in the idea. (from 2 & 3)
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This principle is supposed to follow from the fact that
– An idea must have a cause and although one idea may be derived from others this
cannot go on to infinity; there must be a cause for these ideas.
– Where could an effect get its reality if not from its cause
– How could a cause give something unless it had it
– “However imperfect the existence of something that exists subjectively in the
understanding through an idea, it obviously is something, and it therefore cannot come
from nothing” (Med III)
Questions here?
Continuing the Evaluation
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Evaluating Descartes argument cont.:
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Premise 5: I am a substance who is not infinitely perfect.
Premise 6: I could not be the cause of this idea. (from 1, 4 & 5)
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This is supposed to follow from 4 & 5 in particular but this premise seems entirely questionable
as some believe that God was an idea created by man…
And consider the power of imagination
So maybe the rule doesn’t work for ideas?
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Descartes response: “we cannot grasp the infinite from the finite because there is more reality
in the infinite than in a finite substance and hence that my grasp of the infinite must somehow
be prior to my grasp of the finite--my understanding of God prior to my understanding of
myself.”
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Counter: He is assuming the great chain of being operates in our understanding…
Premise 7: So there must be a formal reality that is an infinitely perfect substance (from
1, 4 & 6)
Premise 8: So God exists (from 7)
Descartes second argument
for God’s existence
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Descartes second argument for God’s existence:
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1. I exist
2. There must be a cause for my existence.
3. The cause must be one of the following: (a) myself, (b) my always having existed, (c)
my parents, (d) something else less perfect than God or (e) God.
4. The cause cannot be myself.
5. The cause cannot be my always having existed.
6. The cause cannot be my parents.
7. The cause cannot be something less perfect than God.
8. Therefore the cause is God. Thus, God exists.
Understanding the Second argument
for God’s existence
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Descartes argument:
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1. I exist
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2. There must be a cause for my existence.
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Something cannot come from nothing
The fact that I existed a little while ago does not entail that I exist now, unless a cause recreates
me at this moment.
It takes like power to preserve a thing at each moment as it does to create it anew if it had
never existed.
Questions about this?
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3. The cause must be one of the following: (a) myself, (b) my always having
existed, (c) my parents, (d) something else less perfect than God or (e) God.
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4. The cause cannot be myself.
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If I am my own cause I wouldn’t have denied myself any of the perfections that I grasp in the
idea of God. Thus, I would be God.
Question: could I cause my own preservation while something else caused my coming to be?
The middle of the argument
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The middle of Descartes 2nd argument:
– 5. The cause cannot be my always having existed.
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The fact that I existed a little while ago does not entail that I exist now, unless a cause recreates
me at this moment.
It takes like power to preserve a thing at each moment as it does to create it anew if it had
never existed.
6. The cause cannot be my parents.
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My parents don’t preserve me. They merely formed the matter in which I formerly resided.
Question:
– If I am the cause of my own persistence might my parents be the cause of my coming to
be?
The end of the argument
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The end of the argument:
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7. The cause cannot be something less perfect than God.
• Since the cause must have at least as much reality as the effect & since I am a
thinking thing with the idea of a perfect God in me it follows that my cause must
be a thinking thing having in it the idea of every perfection I attribute to God.
• If this thing gets its existence from itself it is God.
• If it gets its existence from another then we can ask what caused the existence of
this thing and so on…
• And this cause cannot be several partial causes for although this might account
for my having the ideas of each of the various perfections I attribute to God, this
would not account for the fact that I attribute to him unity, simplicity and
inseparability apart from all of his perfections.
• Question:
– It isn’t at all clear that the reality of an idea must be present formally in its cause…
– Why can’t ideas of perfections be attached to unity…
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8. Therefore the cause is God. Thus, God exists.
Descartes 3rd argument for
God’s existence:
the Ontological Argument
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Descartes’ version of the Ontological argument:
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Comes in the Meditation V
1. God, by definition, is a being of infinite perfection
2. Existence is a perfection (a being wouldn’t be perfect if it lacked existence.)
3. Thus, God exists.
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Evaluating the argument:
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Questioning premise 2: Is existence a property?
God’s existence
justifying
the non-basic beliefs
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God wouldn’t allow me to be deceived:
– Descartes thinks God wouldn’t allow me to be radically mistaken about the
nature of the world.
• And Descartes thinks God wouldn’t allow me to be deceived by an evil demon.
– So the skeptical scenario’s cannot cast doubt on my beliefs.
– Thus, my belief that God exists justifies lots of my other beliefs:
• sense experience, logic, inferences and arguments…
Descartes’ argument for the truth of
beliefs about sense experience
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So Descartes thinks that God exists and wouldn’t allow me to be radically mistaken about
the nature of the world.
– God wouldn’t allow a skeptical scenario to be true…
But since I am not radically mistaken about the nature of the world Descartes thinks it
follows that I can be justified in beliefs about sense perceptions: (Med. VI)
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1. I have a strong inclination to believe in the reality of the material things that I seem to
sense.
2. God must have created me with this inclination.
3. If material things do not exist independently then God is a deceiver.
4. But God is not a deceiver.
5. So material things exist with those properties I conceive to be essential to them.
Evaluating Descartes argument
for material objects
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Evaluating Descartes argument for material objects:
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1. I have a strong inclination to believe in the reality of the material things that I seem to
sense.
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2. God must have created me with this inclination.
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This follows from God’s existence and his not being a deceiver…
3. If material things do not exist independently then God is a deceiver.
4. But God is not a deceiver.
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The light of nature indicates that I sense objects distinct from my thought for these ideas come
to me independent of my desires such that I couldn’t sense an object when it wasn’t present to
my senses nor could I fail to sense one when it was present.
“…since He has given me a strong inclination to believe that the ideas come from physical
objects, I see no way to avoid the conclusion that He deceives me if the ideas are sent to me by
anything other than physical objects. It follows that physical objects exist.” (Med. VI)
5. So material things exist with those properties I conceive to be essential to them.
Where does
Descartes go now?
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Problems for Descartes:
– Descartes attempt at justifying all the non-basic beliefs is dubious:
• Few people think that the ontological argument is sound.
• And the other 2 arguments for God’s existence have their problems.
• And Descartes says that the evil demon could make good mathematical proofs
seem bad to me, and bad ones seem good.
– But Descartes arguments for God’s existence are difficult proofs.
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Replies for Descartes:
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Maybe one of his 3 arguments is defensible…
The Problem of the criterion
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The problem of the criterion:
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The Cogito is the basis for Descartes’ criterion. He first introduces the criterion in
Meditation III.
Descartes knows the cogito. He knows it with certainty. He takes this knowledge as a
model by which to judge other beliefs.
1. Descartes is certain that he exists as a thinking thing.
2. Descartes asks himself, What is it about this proposition that accounts for my
certainty that it is true?
3. His answer: the fact that I grasp it so clearly and distinctly that I perceive it could not
possibly be false.
4. He concludes: let this be the criterion: whatever I grasp with like clarity and
distinctness must also be true.
The Criterion: clear and distinct perceptions
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Clear and distinct perceptions:
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So Descartes holds that anything which he perceives clearly and distinctly is true.
The perception must be as clear and distinct as the way in which he perceives the cogito.
• For a belief to be clear:
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something is clear when it is “present and apparent to an attentive mind, in the same way as we assert that
we see objects clearly when, being present to the regarding eye, they operate upon it with sufficient
strength.” (Principles of Philosophy, 1.45)
We don’t accept beliefs that are fuzzy, obscure, dim, vague, indefinite, indistinct, etc.
Apple example…
For a belief to be distinct:
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Distinct: “so precise and different from all other objects that it contains within itself nothing but what is
clear”.
It must be impossible to confuse the idea with any other idea
Triangle and Square example…
Descartes on Error
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Descartes on Error:
– Descartes has just told us that anything which we clearly and distinctly perceive is true.
– In Meditation III (& V) Descartes thinks he has proven not only that God exists but that
God isn’t a deceiver and so why would have God given me an ability that goes wrong?
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Error: when the will reaches beyond the grasp of understanding…
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Judgments: my will assenting to believe some proposition, which is or isn’t understood
Understanding: my ability to grasp ideas about which I form judgments
•
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The will: my ability to freely assent to believing a proposition
•
–
The understanding is restricted…
The will is unrestricted…
Error: “while my will has a broader scope than my understanding, I don’t keep it within
the same bounds, but extend it to that which I don’t understand.” “(Med IV)
•
If I suspend judgment when I don’t clearly and distinctly grasp what’s true, I obviously do right
and am not deceived…
Clear and distinct perceptions
and God’s existence
•
So we can avoid error by believing only what I understand clearly and distinctly.
– But this is so because God is not a deceiver.
– And yet God has given me the abilities to will and to understand.
– So when I use these abilities correctly I never err.
– So clear and distinct perceptions are always true because they come from God.
•
How do we avoid error then: “when I limit my will’s range of judgment to the things presented
clearly and distinctly to my understanding, I…cannot err--for everything that I clearly and
distinctly grasp…must come…from God…who cannot possibly deceive. Therefore, what I
clearly and distinctly grasp is unquestionably true.” (Med IV)
•
“But now that I grasp that God exists, and I understand both that everything else depends on
Him and that He’s not a deceiver. From this, I infer that everything I clearly and distinctly grasp
must be true.” (Med V)
Final thoughts on Descartes
•
Does Descartes solve the problem of the criterion?
–
His criterion is this:
• Anything which he perceives clearly and distinctly is true.
• The perception must be as clear and distinct as the way in which he perceives the
cogito.
–
He justifies this criterion in virtue of the fact that his perception of the cogito is
clear and distinct. So the cogito is a model for knowledge.
–
He then infers other beliefs from this criterion:
• The mind and body are distinct:
– Because if God can create one thing independently of another, the first thing is distinct
from the second and because he has a C&D idea of his essence as a thinking thing while
he has a C&D perception of his body as an extended thing it follows that mind and body
are distinct… (Med. VI)
More thoughts on the criterion
•
He also infers from the criterion:
– The existence of God as perfect entity:
•
•
–
–
•
“Surely, I find the idea of God, a supremely perfect being, in me…clearly and distinctly” “I
understand as clearly and distinctly that eternal existence belongs to his nature…” (Med. V)
“my idea of God…is maximally clear and distinct, for it contains everything that I grasp clearly
and distinctly, everything real and true, everything with any perfection.” Med III
Material objects must at least have in them everything that I clearly and distinctly
understand them to have… (Med. VI)
The Primary Qualities: “What I do grasp clearly and distinctly in these ideas is
size…shape…position…motion…substance, duration, and number.“(Med III)
But we can still ask: does he really provide sufficient justification for the criterion?
– Just because the cogito is true and just because we perceive it clearly and distinctly, it
needn’t follow that other beliefs that are perceived in a similar way are likewise true.