History of Philosophy Lecture 13 Descartes

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History of PhilosophyLecture 13Descartes

• By David Kelsey

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The Copernican Revolution

• The Copernican Revolution
• Begun by Copernicus (1473-1543). Published De
  Revolutionibus in 1543.
• Prior to Copernicus, Ptolemys 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

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Kepler

• Johannes Kepler
• 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.
• Keplers 3 laws
• 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
  semi-major axis of its orbit.

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Galileo Galilei

• Galileo Galilei
• 1564-1642
• The telescope
• Gives us a mathematical theory of motion

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Implications of the Copernican Revolution

• Implications of the Copernican Revolution
• The universe is thought of as infinitely extended
  in space so it has no center
• The heavens arent 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?

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The Churchs response to Galileo the
Copernican Revolution

• The Churchs response to Galileo the Copernican
  Revolution
• In 1616 Galileo ordered by the court to not
  defend the Heliocentric view
• In 1632 Galileo publishes Dialogue Concerning the
  Two Chief World Systems
• In 1633 Galileo was was found guilty of holding
  and defending the heliocentric view.
• In 1633 the Church prohibits any teachings or
  holdings of the heliocentric view

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Descartes

• Rene Descartes
• lived from 1596-1650.
• Was an important mathematician, physicist and
  philosopher.
• Considered to be the father of modern philosophy
• His Meditations are one of the most influential
  works in all of philosophy.

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Descartes response to Galileo

• 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 Galileos
  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 wouldnt 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.

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Skepticism

• 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

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The Skeptical Problem of the Criterion

• 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.

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Refuting the skeptic

• So a skeptic is someone who denies that we know
  anything.
• The skeptic doesnt deny that we believe many
  things that may well be true.
• Rather, they deny that our beliefs are ever
  justified.
• The problem of the criterion
• An Epistemological project refute the skeptic
• 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.

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Descartes method to refuting the skeptic

• So Descartes aims at refuting the skeptic
• Before we get to his refutation lets 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 dont 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.

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Descartesmethod of doubt

• Descartes project refute the skeptic
• 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
• 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 neednt 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.

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Two arguments for skepticism

• The first Meditation
• In the 1st meditation Descartes gives two very
  powerful skeptical arguments
• The Skeptical arguments
• The dream argument
• The evil demon argument
• Remember, he gives these arguments so that he can
  later refute them.

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The Dream argument

• Skeptical Scenario
• If youre dreaming right now, youre not in a
  philosophy lecture youre at home in bed.
• But, for all you can tell, you might be dreaming
  that youre in a lecture.
• The argument
• 1. If I dont know that Im not dreaming, then I
  dont know that Im in a lecture.
• 2. I dont know that Im not dreaming.
• 3. Thus, I dont know that Im in a lecture.
• Notice that this argument tries to show that you
  dont know that youre in a philosophy lecture
  right now.
• But, of course, it can be used to cast doubt on
  lots of other beliefs.

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The Dream ArgumentPremise 1

• 1. If I dont know that Im not dreaming, then I
  dont know that Im 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

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The Dream argumentpremise 2

• 2. I dont know that Im not dreaming.
• 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
• Are dream experiences indistinguishable from
  waking ones?
• Is there any knowledge that cant be called into
  question this way?

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The evil demonargument

• The Evil Demon
• 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
• 1. If I dont know that Im not a victim of an
  evil demon, then I dont know that Im in a
  lecture.
• 2. I dont know that Im not a victim of an evil
  demon.
• 3. Thus, I dont know that Im in a lecture.

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The evil demon 2

• The evil demon argument
• 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 arent to do with your experiences.
• The laws of logic
• Other skeptical scenarios not discussed by
  Descartes

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Whats the skeptic up to?

• Skeptical arguments
• What is the aim of a skeptical argument anyway?
• The aim of a skeptical argument isnt 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 dont know.
• So the skeptic says No-one knows anything,
  no-one is justified in any belief.

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How can we replyto the skeptical arguments?

• Possible replies to the skeptic
• We could embrace skepticism.
• We could deny premise 2 of the argument with
• Descartes Foundationalism
• Descartes tries to show that there are some
  things even an evil demon cant deceive me about.
  
• He then concludes that because he cant be
  deceived about these things, there cannot be an
  evil demon.

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Skepticism

• 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 isnt just
  another name for justification.

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Denying premise 2

• To answer the skeptic by denying premise 2
• we have to show how our beliefs are justified.
• How are beliefs justified?
• Beliefs are sometimes justified by other beliefs.
• My neighbor is walking about
• The justifying belief also has to be justified
  itself.
• My neighbor again
• 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

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Foundationalism

• Descartes was a Foundationalist.
• 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.
• 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

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Foundationalismrefuting the skeptic

• 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.

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The Cogito

• The Cogito
• Descartes thinks that even the evil demon
  couldnt deceive him about whether he (Descartes)
  exists.
• If there is a deceiverthen surely I exist,
  since I am deceived
• Descartes famous slogan
• I think, therefore I am.
• In Latin, Cogito ergo sum.
• 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.

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The cogito 2

• We saw that for Descartes I exist is a basic
  belief.
• The truth of this belief 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.
• 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.

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The Cogito self justifying

• 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.
• Only I exist is guaranteed true
• Descartes exists isnt so guaranteed.
• Descartes could be an illusion after all.
• But in believing I exist
• the evil demon couldnt deceive this I that is
  thinking about whether this I exists.
• For such deception presupposes an I to be
  deceived.

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The cogito as an argument

• The cogito is an argument
• 1. I am thinking.
• 2. Thus, I exist.
• Even the skeptic has to recognize this argument
  as sound!!!
• Its premise is true and it cannot be doubted for
  it is self justifying.
• To say the cogito is self justifying is to say
  that you can know it to be true by just thinking
  about it.
• In other words, the cogito gives you a reason for
  believing it.

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Objection 1Does anyone exist?

• Does anyone exist at all?
• Descartes is certain that he exists--that belief
  in his existence is skeptic-proof.
• But its 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 isnt certain that anyone exists at
  all.
• Descartes reply
• I didnt say that Descartes exists is skeptic
  proof.
• Its I exist thats skeptic proof.

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Objection 2Whats special about the cogito?

• Theres nothing special about the cogito.
• Its no more nor less sound than this argument
• 1. I am walking.
• 2. Therefore, I exist.
• But nobody would mistake that for a refutation of
  skepticism.
• Descartes reply
• I am walking is not a self-justifying belief.

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Objection 3Does thought require a thinker?

• Couldnt the evil demon create the thought I am
  thinking without creating a thinker?
• If so, then I am thinking is not
  self-justifying.
• Descartes reply
• Thats absurd, you cant have a thought without a
  thinker.
• Counter to Descartes
• But now isnt Descartes using another belief,
  that you cant have a thought without a thinker,
  to justify the cogito?

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Finishing Descartes program

• The Foundationalism project
• Recall that the Foundationalist has to do three
  things
• 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.
• Weve just been looking very closely at
  Descartes attempt at the second part of this.
• But what about the third part?
• How could the cogito justify other non-basic
  beliefs?

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Descartes andthe justification of non-basic
beliefs

• Descartes would himself agree that the cogito
  alone is too narrow a basis for the whole of our
  knowledge.
• 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

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Solipsism

• Solipsism
• 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.
• 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 isnt 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)

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Descartes arguments forGods existence

• Descartes arguments for Gods existence
• In the 3rd Meditation, Descartes gives 2
  arguments for Gods existence. Here is the
  first
• 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)

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Formal and subjective reality

• Descartes argument assumes the notions of formal
  and subjective reality
• Premise 4 of Descartes argument makes use of the
  notions of formal and subjective reality
• Formal Reality
• 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
• When you entertain an idea your thoughts have
  subjective reality reality for you.
• Some objects have only subjective reality the
  tooth fairy

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Evaluating Descartes first argumentfor Gods
existence

• Evaluating Descartes argument
• Premise 1 I have an idea of an infinitely
  perfect substance.
• Premise 2 Such an idea must have a cause.
• 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)
• 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?

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Continuing the Evaluation

• Evaluating Descartes argument cont.
• 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)
• 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 doesnt work for ideas?
• 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.
• 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)

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Descartes second argumentfor Gods existence

• Descartes second argument for Gods existence
• 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.

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Understanding the Second argumentfor Gods
existence

• Descartes argument
• 1. I exist
• 2. There must be a cause for my existence.
• 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?
• 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.
• If I am my own cause I wouldnt 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?

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The middle of the argument

• The middle of Descartes 2nd argument
• 5. The cause cannot be my always having existed.
• 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.
• My parents dont 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?

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The end of the argument

• The end of the argument
• 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 isnt at all clear that the reality of an idea
  must be present formally in its cause
• Why cant ideas of perfections be attached to
  unity
• 8. Therefore the cause is God. Thus, God exists.

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Descartes 3rd argument forGods existence the
Ontological Argument

• Descartes version of the Ontological argument
• Comes in the Meditation V
• 1. God, by definition, is a being of infinite
  perfection
• 2. Existence is a perfection (a being wouldnt be
  perfect if it lacked existence.)
• 3. Thus, God exists.
• Evaluating the argument
• Questioning premise 2 Is existence a property?

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Gods existence justifying the non-basic beliefs

• God wouldnt allow me to be deceived
• Descartes thinks God wouldnt allow me to be
  radically mistaken about the nature of the world.
• And Descartes thinks God wouldnt allow me to be
  deceived by an evil demon.
• So the skeptical scenarios cannot cast doubt on
  my beliefs.
• Thus, my belief that God exists justifies lots of
  my other beliefs
• sense experience, logic, inferences and
  arguments

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Descartes argument for the truth of beliefs
about sense experience

• So Descartes thinks that God exists and wouldnt
  allow me to be radically mistaken about the
  nature of the world.
• God wouldnt 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)
• 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.

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Evaluating Descartes argumentfor material objects

• Evaluating Descartes argument for material
  objects
• 1. I have a strong inclination to believe in the
  reality of the material things that I seem to
  sense.
• 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
  couldnt sense an object when it wasnt present
  to my senses nor could I fail to sense one when
  it was present.
• 2. God must have created me with this
  inclination.
• This follows from Gods 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.
• 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.

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Where does Descartes go now?

• 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 Gods 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 Gods existence are
  difficult proofs.
• Replies for Descartes
• Maybe one of his 3 arguments is defensible

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Descartes philosophy of mind

• Descartes philosophy of mind
• Descartes was a dualist. A dualist
• Says there are two kinds or type of thing,
  physical things and mental things.
• Your body is physical and your mind is mental, so
  they are distinct.
• The mind is the soul
• Reincarnation
• ghosts, angels, demons, astral projections
• His brand of Dualism is known as Interactionism.
• He thought the mind and body interacted in the
  Pineal gland of the brain.
• Although Descartes is a Dualist, one could hold
  on to the view that is known as Physicalism.
  Physicalism
• Says everything is physical or material
  substance.
• This means that if there is such a thing as your
  mind at all, it is a physical object, presumably
  your body or part of it.

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Descartes 1st argument for Dualism

• Descartes was famously a dualist, and his second
  Meditation contains one of his arguments for
  dualism.
• 1. I can doubt that my body exists.
• His argument for this premise comes in his evil
  demon argument
• I will supposethat there is an evil demon,
  supremely powerful and cunning, who works as hard
  as he can to deceive meI will regard myself as
  not having hands, eyes, flesh, blood, and
  senses(late in Meditation 1)
• I cant say I am the collection of organs that
  we call a human bodyfor I have supposed that
  none of these things exist. (mid 2nd meditation)
• 2. I cannot doubt that my mind exists.
• His argument for this premise comes in his cogito
  argument.
• Thinking? It comes down to this. There is
  thinking, and thought alone cannot be taken away
  from meI am therefore not admitting that I am
  anything at all other than a thinking thing--that
  is, a mind, soul, understanding, or reasonI know
  that I ama thing that thinks. (mid 2nd
  meditation)
• 3. Thus, my mind is not the same thing as my body.

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The validity of Descartes argument

• Descartes is appealing to a principle now called
  Leibnizs law
• If x and y are identical, then anything you can
  truly say about x, you can truly say about y.
• So If Bob Dylan is the same person as Robert
  Zimmerman, then whatever I can say about Dylan, I
  can say about Zimmerman.
• So if Dylan is the worlds greatest folk singer,
  then Zimmerman is the worlds greatest folk
  singer.
• The physicalist is saying my mind and my body
  are like Dylan and Zimmerman--two names for
  one and the same thing.
• So shouldnt the physicalist say that if I can
  doubt that my body exists, then I can doubt that
  my mind exists too?

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Descartes 2nd argument for Dualism

• Late in the 6th Meditation
• I will note that mind differs importantly from
  body in that body is by its nature divisible,
  while mind is indivisible. When I think about my
  mind--or, in other words, about myself insofar as
  I am a thinking thing--I cant distinguish any
  parts I understand myself to be a single,
  unified thing. Although my whole mind seems
  united to my whole body, I know that cutting off
  a foot, arm, or other limb would not take
  anything away from my mind. And the abilities to
  will, sense, understand cant be called parts,
  since it is one and the same mind that wills,
  senses, and understands. On the other hand,
  whenever I think of a physical or extended thing,
  I can mentally divide it, and I therefore
  understand that the object is divisible. This
  single fact would be enough to teach me that my
  mind and my body are distinct
• The formalized argument
• 1.) Body is divisible
• Whenever I think of a physical or extended thing,
  I can mentally divide it
• 2.) Mind is indivisible
• The mind has no parts it is one and the same
  mind that wills, senses and understands.
• 3.) If x and y are identical, then anything you
  can truly say about x, you can truly say about y.
• 4.) My mind is not the same thing as my body.

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Questions about Descartes 2nd argument

• What about premise 2?
• Premise 1?
• But what about premise 2?
• Is it true that the mind is indivisible?
• If science tells us the brain is divisible
  doesnt it follow that the mind is as well?

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Descartes 3rd argument for Dualism

• Descartes third argument, the real distinction
  of mind and body
• 1. God can create anything that I can clearly and
  distinctly conceive--there being no impossibility
  in it.
• 2. If God can create one thing independently of
  another, the first thing is distinct from the
  second.
• 3. I have a clear and distinct idea of my essence
  as a thinking thing.
• 4. So God can create a thinking thing (a soul)
  independent of a body. (from 1 3)
• 5. I also have a clear and distinct idea of my
  body as an extended thing--its essence.
• 6. So God can create a body independently of a
  soul. (from 1 5)
• 7. So my soul is a reality distinct from my body.
  (from 4 6)
• 8. So I, as thinking thing (soul), can exist
  without my body. (from 7)

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Understanding the argument for thereal
distinction Descartes criterion

• In Descartes argument for the real distinction,
  he makes use of his criterion for truth
• 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.

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The Criterion clear and distinct perceptions

• Clear and distinct perceptions
• 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
• 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 dont accept beliefs that are fuzzy, obscure,
  dim, vague, indefinite, indistinct, etc.
• Apple example
• For a belief to be distinct
• 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

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Descartes on Error

• 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
  isnt a deceiver and so why would have God given
  me an ability that goes wrong?
• Error when the will reaches beyond the grasp of
  understanding
• Judgments my will assenting to believe some
  proposition, which is or isnt understood
• Understanding my ability to grasp ideas about
  which I form judgments
• The understanding is restricted
• The will my ability to freely assent to
  believing a proposition
• The will is unrestricted
• Error while my will has a broader scope than my
  understanding, I dont keep it within the same
  bounds, but extend it to that which I dont
  understand. (Med IV)
• If I suspend judgment when I dont clearly and
  distinctly grasp whats true, I obviously do
  right and am not deceived

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Clear and distinct perceptionsand Gods 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
  wills range of judgment to the things presented
  clearly and distinctly to my understanding,
  Icannot err--for everything that I clearly and
  distinctly graspmust comefrom Godwho 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 Hes not a deceiver. From this, I
  infer that everything I clearly and distinctly
  grasp must be true. (Med V)

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Understanding Evaluating the argumentfor the
real distinction of mind and body

• Explanation of the argument
• 1. God can create anything that I can clearly and
  distinctly conceive--there being no impossibility
  in it.
• 2. If God can create one thing independently of
  another, the first thing is distinct from the
  second.
• Anything that is clearly and distinctly perceived
  can be made by God to be exactly as it is
  perceived.
• But if I clearly and distinctly understand one
  thing apart from another it follows that these
  things could really be separated by God and so
  they are distinct.
• Questions
• 3. I have a clear and distinct idea of my essence
  as a thinking thing.
• The cogito
• 4. So God can create a thinking thing (a soul)
  independent of a body. (from 1 3)
• A body-less soul

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Understanding Evaluatingthe end of the argument

• Understanding the end of the argument
• 5. I also have a clear and distinct idea of my
  body as an extended thing--its essence.
• He perceives clearly and distinctly that body is
  extended
• 6. So God can create a body independently of a
  soul. (from 1 5)
• A Corpse or Zombie
• 7. So my soul is a reality distinct from my body.
  (from 4 6)
• 8. So I, as thinking thing (soul), can exist
  without my body. (from 7)
• Question
• Must it follow from the conclusion that the soul
  and body are different substances altogether?
• What if both mind and body are material but are
  distinct in some other way?

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Descartes Interactionism

• Descartes view
• So Descartes holds that each of us has a physical
  part (the body) and a mental part (the soul).
• Descartes was an Interactionist.
• Interactionism says that minds and bodies
  causally interact
• For example, when the nerves in the foot are
  moved with unusual violence, the motion is
  communicated through the middle of the spine to
  the center of the brain, where it signals the
  mind to sense a pain in the foot. This urges
  the mind to view the pains cause as harmful to
  the foot and to do what it can to remove the
  cause. (end of the 6th meditation)
• Minds cause things to happen to bodies.
• When you act, your mind causes your body to move.
• Bodies can cause things to happen to minds.
• When you experience the physical world, your body
  is relaying your sensations to your mind.
• According to Descartes, the interactions take
  place in the pineal gland.

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Problems for Descartesthe problem of interaction

• Spooky causation
• If Interactionism were true, bodies would have to
  behave in ways that cant be explained in
  physical terms.
• Given the mind can cause the body to act it
  follows that the mental can cause the physical to
  act.
• But this would be a very weird kind of causation
  indeed! It would be spooky causation.
• So there would have to be exceptions to the
  causal laws normally governing physical things.
• Causal laws
• But human bodies (even pineal glands!) appear to
  obey those laws just like the rest of the
  physical world.
• Think of the circulatory system
• Possible Dualist response
• Deny that minds ever cause anything physical to
  occur.
• This is not Descartes move.
• This is called Epiphenomenalism.

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Problems for Descartesthe problem of other minds

• The problem of other minds
• I cant doubt that I have a mind.
• But I can doubt that you have one, just as I can
  doubt that you have a body.
• For all Descartes argument shows, I might be the
  only human being with a mind.
• How do I know that Im not?
• This is called the problem of other minds.
• Are people just meat machines?
• Descartes held that animals (other than humans)
  are entirely physical.
• They are meat machines.
• It seems as though theres no way to know that
  other people arent just meat machines too.

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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 CD idea of his
  essence as a thinking thing while he has a CD
  perception of his body as an extended thing it
  follows that mind and body are distinct (Med. VI)

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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 meclearly and distinctly I
  understand as clearly and distinctly that eternal
  existence belongs to his nature (Med. V)
• my idea of Godis 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
  sizeshapepositionmotionsubstance, 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 neednt
  follow that other beliefs that are perceived in a
  similar way are likewise true.