Skepticism

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• Questions for Discussion!
• Do you agree with Henry that Jack doesnt know
  that his battery is dead?
• Do you agree with Henry about his general
  principle (In general, you cant know)?
• Regardless of whether you agree with him, did
  Henry kind of get on your nerves?
• Did you sort of want to slap him around a little
  bit?

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Guiding Question

• What can we know?

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Metaphysics

• Metaphysics is the study of the nature of
  reality.
• (The study of how things really are)
• Some metaphysical questions
• Do tables and chairs exist?
• Does god exist? If so, what is he/she/it really
  like?
• What is the nature of the self?
• Do we have free will?

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Epistemology

• The study of the nature of knowledge.
• Some epistemological questions
• What is knowledge?
• Does anyone know anything at all?
• What does it take for a belief to be justified?

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• SEVERAL years have now elapsed since I first
  became aware that I had accepted, even from my
  youth, many false opinions for true, and that
  consequently what I afterward based on such
  principles was highly doubtful and from that
  time I was convinced of the necessity of
  undertaking once in my life to rid myself of all
  the opinions I had adopted, and of commencing
  anew the work of building from the foundation, if
  I desired to establish a firm and abiding
  superstructure in the sciences To-day, then, I
  will at length apply myself earnestly and freely
  to the general overthrow of all my former
  opinions.
• -Descartes, Meditation One

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Descartes 3-Step Method

• 1.Tear down all of his beliefs.
• 2.Find sturdy foundations.
• 3.Build back up. (establish a firm and abiding
  superstructure in the sciences).

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• But, to this end, it will not be necessary for
  me to show that the whole of these are false--a
  point, perhaps, which I shall never reach but as
  even now my reason convinces me that I ought not
  the less carefully to withhold belief from what
  is not entirely certain and indubitable, than
  from what is manifestly false, it will be
  sufficient to justify the rejection of the whole
  if I shall find in each some ground for doubt.
  Nor for this purpose will it be necessary even to
  deal with each belief individually, which would
  be truly an endless labor but, as the removal
  from below of the foundation necessarily involves
  the downfall of the whole edifice, I will at once
  approach the criticism of the principles on which
  all my former beliefs rested.
• -Descartes, Meditation One

8

• But, to this end, it will not be necessary for
  me to show that the whole of these are false--a
  point, perhaps, which I shall never reach but as
  even now my reason convinces me that I ought not
  the less carefully to withhold belief from what
  is not entirely certain and indubitable, than
  from what is manifestly false, it will be
  sufficient to justify the rejection of the whole
  if I shall find in each some ground for doubt.
  Nor for this purpose will it be necessary even to
  deal with each belief individually, which would
  be truly an endless labor but, as the removal
  from below of the foundation necessarily involves
  the downfall of the whole edifice, I will at once
  approach the criticism of the principles on which
  all my former beliefs rested.
• -Descartes, Meditation One

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Descartes Goal

• Descartes wants to achieve certainty in all of
  his beliefs.
• (He wants to construct a belief system that is
  completely immune from error.)

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Descartes 3-Step Method

• 1.Tear down all of his beliefs. (Doubt everything
  that can be doubted.)
• 2.Find sturdy foundations. (Find those beliefs
  which are certain and indubitable.)
• 3.Build back up. (Infer other beliefs from the
  "foundational" beliefs.)

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General Principle for Knowledge?

• Descartes quest for certainty has often been read
  as a view about the requirements for knowledge.
• On this view, knowledge requires certainty.
• Ill refer to this view as Descartes Rule-Out
  Principle for knowledge
• If you can't rule-out every possibility on which
  X is false, then you do not know that X is true.
• Or, to put it a slightly different way

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• All that I have, up to this moment, accepted as
  possessed of the highest truth and certainty, I
  received either from or through the senses. I
  observed, however, that these sometimes misled
  us and it is the part of prudence not to place
  absolute confidence in that by which we have even
  once been deceived.
• -Descartes, Meditation One

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Deception Argument

• Premise 1 The senses sometimes deceive us.
• --------------------------------------------------
  ------
• Conclusion So for all we know, they always
  deceive us.

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• How often have I dreamt that I was in these
  familiar circumstances, that I was dressed, and
  occupied this place by the fire, when I was lying
  undressed in bed? At the present moment, however,
  I certainly look upon this paper with eyes wide
  awake the head which I now move is not asleep I
  extend this hand consciously and with express
  purpose, and I perceive it the occurrences in
  sleep are not so distinct as all this. But I
  cannot forget that, at other times I have been
  deceived in sleep by similar illusions and,
  attentively considering those cases, I perceive
  so clearly that there exist no certain marks by
  which the state of waking can ever be
  distinguished from sleep, that I feel greatly
  astonished and in amazement I almost persuade
  myself that I am now dreaming.
• -Descartes, Meditation One

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• How often have I dreamt that I was in these
  familiar circumstances, that I was dressed, and
  occupied this place by the fire, when I was lying
  undressed in bed? At the present moment, however,
  I certainly look upon this paper with eyes wide
  awake the head which I now move is not asleep I
  extend this hand consciously and with express
  purpose, and I perceive it the occurrences in
  sleep are not so distinct as all this. But I
  cannot forget that, at other times I have been
  deceived in sleep by similar illusions and,
  attentively considering those cases, I perceive
  so clearly that there exist no certain marks by
  which the state of waking can ever be
  distinguished from sleep, that I feel greatly
  astonished and in amazement I almost persuade
  myself that I am now dreaming.
• -Descartes, Meditation One

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The Dreaming Argument

• P1 I cannot rule out the possibility that I am
  merely dreaming that there is a cup on the table
  in front of me (because there exist no certain
  marks by which the state of waking can ever be
  distinguished from sleep).
• P2 If I cannot rule out this possibility, then I
  do not know that there is a cup on the table in
  front of me. (The rule-out principle.)
• -------------------------------------------------
  -------------
• C Therefore, I do not know that there is a cup
  on the table in front of me.

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The Evil Demon Argument

• P1 I cannot rule out the possibility that an
  evil demon is deceiving me into thinking that
  there is a cup on the table in front of me.
• P2 If I cannot rule out this possibility, then I
  do not know that there is a cup on the table in
  front of me. (The rule-out principle.)
• -------------------------------------------------
  -------------
• C Therefore, I do not know that there is a cup
  on the table in front of me.