Rene Descartes 15961650

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Rene Descartes15961650
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Some dates

• 1543 publication of Copernicuss De
  Revolutionibus
• 1633 Galileo arrested
• 1641 publication of the Meditations

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Some reasons to doubt the senses

• Past error
• Insanity/delusion
• Dreams
• Possibility of demon/evil genius/malicious god

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How do these lead us to doubt the senses?

• All our knowledge of the external world is based
  on sense experience
• Unless I have a reason to think my sense
  experience is reliable, I have no reason to
  believe in an external world
• I cant have any reason to think my senses are
  reliable
• Therefore, I have no reason to believe in an
  external world

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What can I know?
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I think therefore I am!
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What am I?
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Plato(428-347BCE)
I am a featherless biped
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Aristotle(384-322BCE)
I am a rational animal
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Descartes
I am a thinking thing!
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Personal IdentityWhat am I?
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Descartes

• I am my mind
• I am essentially rational, only accidentally an
  animal
• The demon thought experiment indicates that I
  could exist even if my body did not, so I am not
  my body

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Metaphysics and Epistemology

• Metaphysics the study of what there is, the
  fundamental nature of reality
• Epistemology theory of knowledge and justified
  belief, reason, evidence, etc.

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Rationalism

• All or most of our knowledge is a priori, i.e.,
  knowable independently of experience, i.e., on
  the basis of pure reason
• Epistemological view
• All or most of our concepts are innate
• Psychological view (aka nativism)

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Empiricism

• All or most of our knowledge is a posteriori,
  i.e., knowable only on the basis of experience
• Epistemological view
• All or most of our concepts are learned
• Psychological view (sometimes called concept
  empiricism)

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Descartess skepticism

• Gives us reason to doubt the senses
• Highlights distinction between appearance and
  reality

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• 1. Nothing is ever directly present to the mind
  except its own ideas (e.g., sense experiences)
• 2. To know anything about the external world, I
  would first have to know these ideas accurately
  represent the external world
• 3. But I couldnt have any non-question-begging
  reason for believing that, thus cant know it
• 4. Therefore, I cant know anything about the
  external world

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• 1. Nothing is ever directly present to the mind
  except its own ideas (e.g., sense experiences)
• 2. To know anything about the external world, I
  would first have to know these ideas accurately
  represent the external world
• 3. But I couldnt have any non-question-begging
  reason for believing that, thus cant know it
• 4. Therefore, I cant know anything about the
  external world

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• If I can come up with an a priori argument for
  the reliability of sense-perception, it wont be
  question-begging

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I think therefore I am!
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What do I know?

• That I think
• That I exist
• That Im thinking about .
• E.g., that Im in pain (understood as purely
  mental), that Im having a visual experience as
  of a desk, etc.
• That I am a thinking thing (that I am my mind)

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• Mind is better known than body, even though
  bodies are perceptible, minds are not
• Surprising, if we confuse understanding with
  imagining

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• Imagination capacity for forming sensory images
  of things (e.g., seeing in the minds eye)
• Understanding capacity for pure, nonsensory
  thought

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triangle
(-2, -4), (3, 7), (1, -5)
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• Not all knowledge involves imagination
• (In fact, none does)
• Why does imagination have such a grip on us?
• Because it gives us clear---though not
  distinct---ideas
• Clear accessible to the attentive mind (opposed
  to obscure)
• Distinct sharply separated from other ideas
  (opposed to confused)

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Wax example

• Piece of wax has a certain taste, odor, size,
  color, shape, texture, solidity, sound.
• Bring it near a heat source and all of these
  change. Still we know that it is the same piece
  of wax.
• Our knowledge of the wax is not through the
  senses but through the intellect alone.
• To perceive the wax is not strictly to see it,
  but to understand it
• The wax itself is an invisible substance that has
  perceptible properties. We cant imagine the wax
  itself, though we can understand it

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What do I know?

• That I know that I think
• That I know that I exist
• So I know something about knowledge
• What does my perception of my own existence have
  that qualifies it for being knowledge?
• That I clearly and distinctly perceive it to be
  true
• Therefore, whatever I clearly and distinctly
  perceive to be true, really is true

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Clarity and Distinctness Principle

• Whatever I clearly and distinctly perceive to be
  true, really is true
• Can we give a more rigorous proof?
• God exists.
• God wouldnt let me be deceived when Im doing my
  very best to avoid error
• The best I can do is assent to only what I
  clearly and distinctly perceive to be true
• Therefore, whatever I clearly and distinctly
  perceive to be true, really is true

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Argument for Gods Existence---Background

• Formal reality/existence existence in fact, real
  existence
• Objective reality/existence existence in thought

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Argument for Gods ExistenceCausal principles
known a priori

• Everything has a cause.
• Some corollaries
• There must be at least as much reality in the
  cause as in the effect.
• (otherwise, part of the effect would be uncaused)
• There must be at least as much formal reality in
  the cause as there is objective reality in the
  effect
• (all causes must have formal reality)

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Argument for Gods Existence

• I have an idea of God, i.e., an infinite being
• This idea has infinite objective reality
• There is as at least as much formal reality in
  the cause as objective reality in the effect
• Therefore, this idea is caused by a thing with
  infinite formal reality
• Therefore, an infinite thing exists
• I.e., God exists

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Argument for reliability of cognitive faculties

• God (exists and) is infinite (from earlier
  argument)
• Therefore, God is perfect (from 1)
• To deceive is to be lacking in some perfection
• Therefore, God is not a deceiver (2, 3)
• God is (directly or indirectly) responsible for
  my existence
• If God allowed me to be mistaken, even when Im
  doing my very best to avoid error, he would be a
  deceiver (5)
• Since hes not a deceiver (4), it must be that
  when Im doing my very best, I cant go wrong (4,
  6)
• The best I can do is to assent to only what I
  clearly and distinctly perceive to be true
• Therefore, what I clearly and distinctly perceive
  to be true really is true (Clarity and
  Distinctness Principle)

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Problem how is it that we ever err?

• By not using judgment properly
• Judgment is really result of two faculties
• Intellect perceives ideas
• Will chooses what to believe
• Intellect is finite, will is infinite
• Since the will extends farther than the
  intellect, it is possible to believe what we
  dont perceive to be true.

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The essence of material things

• Clear and distinct ideas of extension (taking up
  space), motion, duration
• Innate knowledge of numbers figures, movements,
  etc.
• The principles of geometry are clear and
  distinct, thus knowable.
• Mathematics in general more certain than belief
  based on sensation

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Descartess epistemology

• Intuition self-evident knowledge knowledge that
  does not depend on other knowledge (basic
  beliefs)
• Demonstration knowledge that does depend on
  other knowledge (nonbasic beliefs)
• Foundationalism some beliefs are basic
  (noninferentially justified, foundational) and
  all other justified beliefs ultimately derive
  their justification from inferential connections
  to basic beliefs

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• Proof string together intuitions, so that each
  step in the proof is self-evident, can render
  something clear and distinct that wasnt
  previously
• Clarity and distinctness goes away over time,
  becomes possible to doubt
• Existence of God, fact that he is no deceiver,
  ensures that what is or was once clearly and
  distinctly perceived is true
• Knowledge of Gods existence essential for
  perfect knowledge on the basis of proof

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The Cartesian Circle

• Famous objection to Descartes project in
  Meditations
• Descartes assumes at beginning of 3rd Meditation
  that what is clearly and distinctly perceived is
  true
• Uses this to prove Gods existence
• Uses this to prove that what is clearly and
  distinctly perceived is true.
• Problem theres a vicious circularity here
  cant know that God exists unless we already know
  that what we clearly and distinctly perceive is
  true

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Partial solution?

• In proofs, clarity and distinctness goes away
  over time, becomes possible to doubt
• Existence of God, fact that he is no deceiver,
  ensures that what is or was once clearly and
  distinctly perceived is true
• Knowledge of Gods existence essential for
  perfect knowledge on the basis of remembered
  proof
• Atheist geometer can have a sort of knowledge,
  but not the unshakeable knowledge that a theist
  can have

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Return of the External WorldI. My Own Body

• Recall imagination/understanding distinction
• Probabilistic argument for the existence of body
• I could exist/endure without capacity for
  imagination
• Therefore, the imagination depends on something
  distinct from me
• A body conjoined to me could be the means by
  which I imagine things
• No other candidates seem very likely
• Therefore, I probably have a body

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Return of the External WorldII. Other Bodies

• The capacity for sensing that is in me is passive
  (I dont choose to create ideas of sensation)
• Im not the cause of my ideas of sense theyre
  typically involuntary
• There must be some source of these ideas, outside
  of me
• If the real cause is anything other than the
  bodies the ideas are of, then God is a deceiver.
• God is not a deceiver, so there must be bodies

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Return of the External WorldIII. The Nature of
Bodies

• Sensation only tells me that there are bodies,
  gives me clear and distinct ideas of bodies as
  objects of mathematics.
• Anything else I believe is my choice, not Gods
  doing
• Bodies as objects of mathematics
• i.e., bodies insofar as they have a particular
  shape, size, motion, solidity, etc.
• Primary Qualities
• But not insofar as they have particular taste,
  odor, color, sound, etc.
• Secondary Qualities