; Epistemology
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Theory of knowledge and
 EPISTEMOLOGY: The theory of

 (1) What does it mean for a set of beliefs
  to be true? What kinds of truth are there?
 (2) How will we know when our beliefs are
  true? What are the criteria for having
         Two Kinds of Truth
 Traditionally, there are two kinds of
   (2) EMPIRICAL (or Contingent)
 A statement expressing a necessary truth
  cannot possibly be false. Examples:

 All triangles have three sides.
 All bachelors are unmarried.
 No one who believes that God exists is an
           Necessary Truths
 The truth of a necessary truth does not
  depend on what the facts are like;
  necessary truths are always true no matter
  what. Examples:

 Can you ever find a bachelor who is
 Can you ever find a triangle that does not
  have 3 sides?
 Is it possible to find an atheist who
  believes in God?
      Necessary Falsehoods
 We can say similar things about necessary
   Impossible to be true
   Their falsity does not depend on what the
    facts are like; necessary falsehoods are
    always false no matter what
     Necessary Truths and the
        A Priori (ā prē or ē)

 A Priori = prior to experience or
  independent of any experience of facts or
  states of affairs in the world.
 Necessary truths are often said to be true
  a priori, true independent of any particular
        Necessary Truths and
           A Priori Truths
 It is also said that their poof (or
  justification) does not depend on any
  particular facts of the world.
          Necessary Truths and
             Analytic Truths
 Necessary truths are sometimes called
  analytic truths
 Analytic truths are necessarily true because
   (1) The predicate is contained in the concept of
    the subject.
   (2) Denying the truth of the statement leads to a
   (3) Contradictions are impossible and go against
              Analytic Truths
 “All sisters are female” is an analytic truth
  because the predicate “female” is contained
  in the subject “sister.” Why? A sister is
  defined as being a female sibling. So “All
  sisters are female” says the same thing as
  “All female siblings are female.” The
  predicate is contained in the subject. It is
  easy to see that it would be a contradiction to
  say that not all female siblings are female. So
  “All sisters are female” is necessarily true and
  couldn’t possibly be false.
            Analytic Truths
 Example: Fathers are males.
 The concept “male” is in the concept of
  “father” (male parent).
            Analytic Truths
 Example: All electrons are subatomic
 An electron is by definition a certain type
  of subatomic particle. So the concept of a
  subatomic particle is contained in the
  concept of an electron.
Empirical (or Contingent) Truths
 Empirical = having to do with experience
  Contingent = depending on experience
 A statement expressing an empirical truth
  is true in virtue of the facts. An empirical
  statement is empirical because its truth
  value (whether it is true or false) depends
  on what the world is like.
Empirical (or Contingent) Truths
 They can be known to be true only after
  actually looking at (or knowing about) the
  facts of the world. It is possible for an
  empirical truth to be false because of the
 We can say similar things about empirical
Empirical (or Contingent) Truths
 Empirical Statement: Microorganisms live
  on Mars.
 Empirical truth: Over 5 billion people live
  on Earth.
 Empirical falsehood: Germany won WWII.
         Empirical Truths and
          A Posteriori Truths

 A posteriori = with experience or
  depending on experience of the facts
 Empirical truths are sometimes called “a
  posteriori” because empirical truths
  depend on the facts.
Test: A Priori and A Posteriori: Are
 these statements true or false?
 I can know a priori that all bachelors are
 It is impossible to know a priori whether
  New York has more inhabitants than
  Mexico City.
 I can know a priori that there is life on
  other planets.
 All of mathematics is based on a priori
  Test: A Priori and A Posteriori: Are
   these statements true or false?
 Nobody can know through a priori reasoning
  that the Empire State building is the tallest
  building in the world.
 I can know a priori that is someone is shot to
  death, then somebody must have been a
 I can know a priori that a cube must have 12
 I can know a priori that all swans are white.
           Empirical Truths and
            Synthetic Truths
 Empirical truths are sometimes called synthetic
  truths because the predicate of the statement is
  not contained in the subject but is connected to it
  through experience.

 Example: My car has more than 1 gallon of gas
  in it.
 Example: The door to this room is shut.
 Example: George Bush is president.
Test: Analytic or Synthetic Claims?
 All pencils and pens are writing utensils.
 Electrons are the smallest physical
  particles in the universe.
 More than 20 million people died of AIDS
  last year.
 There are more heterosexual humans than
  homosexual humans.
 Earthquakes are natural disasters.
Test: Analytic or Synthetic Claims?
 Dogs and cows are both animals.
 Texas is larger than Oklahoma.
 The average lawyer makes more than
  $70,000 a year.
 All solid spheres have one surface.
 Test: Necessary or Empirical Claim?
 If one multiplies any natural number by 2, the
  resulting number is even.
 The income of the average worker in the US is
  higher than the income of the average worker
  in Europe.
 Every state must have some form of
 Every event has a cause.
 If any nation should ever use nuclear weapons
  again, then millions of people will die.
Test: Necessary or Empirical Claim?
 Every recession in the economy is
  eventually followed by an economic
 If a person freely performs an action, then
  the person can be held responsible for the
 Sugar is sweet.
 All human beings have the same
  fundamental rights.
 All cats are animals.
Test: Necessary or Empirical Claim?
 The moon moves around the earth.
 All US presidents are male.
 The US withdrew from Vietnam in 1975.
 If Frank has more than 2 sisters, then he has
  at least three siblings.
 There are infinitely many prime numbers.
 In order to graduate from Northwestern
  University, one has to take at least 3 English
Necessary and Empirical Truths
 Necessary Truths
   Analytic
   A priori
 Empirical (or contingent) Truths
   Synthetic
   A posteriori
        Knowledge: Three Kinds

   (1) Knowing how
   (2) Knowledge by acquaintance
   (3) Knowing that
   In philosophy, we are almost always
    concerned with (3), the knowing-that kind
    of knowledge.
           Knowing How
 (1) Knowing how (competence knowledge,
  skill knowledge): This has to do with
  knowing how to do something. For
  example, I know how to ride a bike.
  Knowledge by Acquaintance
 (2) Knowledge by acquaintance: This is
  knowledge that one has when one knows
  something or someone directly. For
  example, I know my friend Jack by having
  been in direct contact with him.
            Knowing That
 (3) Knowing that (propositional knowledge,
  descriptive knowledge): This is knowledge
  that something is the case. For example, I
  know that the earth has one moon.
 In philosophy, we are almost always
  concerned with (3), the knowing-that
  kind of knowledge.
   Test: Knowledge: (1) how, (2) by
  acquaintance, or (3) propositional?
 I know exactly how you feel about her death.
 “2+2=4,” I know that for a fact.
 I used to know Peter very well but in recent
  times we have grown apart.
 I’m not afraid to cheat on my exams because
  I know how to cheat without getting caught.
 Test: Knowledge: (1) how, (2) by
acquaintance, or (3) propositional?
 If only I knew more about the Vietnam war.
 My father used to be the smartest man.
  Now, he has Alzheimer’s, and he doesn’t
  know anything anymore.
 You might know something that is in your
  accounting book, but this doesn’t mean
  that you know anything about how to run
  an accounting firm.
    Knowledge: Does Believing
   Strongly Give Us Knowledge?
 Can believing strongly that something
  is true, make it true?
 Simply believing strongly that something is
  true in no way establishes that it is true.
  Strong belief is not the key to having
  knowledge. Do you agree?
 Knowledge: Does Having a True
  Belief Give One Knowledge?
 Suppose you have a true belief. Do you
  have knowledge? Do you know that this
  belief is true?
   Knowledge: True Belief Is Not
      Enough for Knowledge
 Suppose Mike is on the quiz show Who
  Wants To Be a Millionaire? He is asked
  the name of the Greek city-state that
  defeated the Persians in the battle of
  Marathon. Mike doesn’t know ancient
  Greek history or the battle of Marathon.
  But he believes that “Athens” is the
  answer and selects it. It turns out that
  “Athens” is the correct answer. But does
  Mike know that it is the correct answer?
  No, he is merely guessing.
Knowledge: What is needed for it?
 When a belief is appropriately linked to
  truth, then the belief counts as knowledge.
  But what exactly is this link, and what is
  knowledge? Can you think of some beliefs
  that you have that count as examples of
Knowledge: Classical Definition
 Someone S knows that P if and only if:
   (1) S believes that P is true
   (2) P is true
   (3) S is justified in believing that P is true

 We have to add justification. One has to
  have reasons or evidence of some kind to
  establish that the belief is true. Knowledge
  is justified true belief.
      Can you KNOW any of the
  following? (Can you justify any?)
 I know that I have two hands.
 I know that president Bush will never get
 I know that other people experience the
  smell of coffee just like I do.
 I know that Joe Montana is a better
  quarterback than John Elway.
 I know that water is H20.
       Can you KNOW any of the
   following? (Can you justify any?)
 I know that the Bible contains God’s word.
 I know that killing people is wrong.
 I know that George Washington was a US
 I know that dinosaurs existed on the earth in
  the past.
 I know that there are at least 8 planets in our
  solar system.
 I know that Michael Jackson was an
  emotionally troubled man.
                Gettier Cases
 Recently, epistemologists have challenged
  the classical view of knowledge as justified
  true belief. Special cases seem to show that
  having a justified true belief is not sufficient
  for having knowledge. These special cases
  are called Gettier Cases (after the
  philosopher who first introduced them).
         Example Gettier Case
 Imagine that you and another person go to interview
  for a job at Wal-Mart. After your interview, they call
  you into the office and tell you that they are going to
  hire the other person. They let you go. As you leave,
  you see the other person holding two quarters, which
  he puts into his pants pocket. You think to yourself:
  “The person hired for this Wal-Mart job has fifty cents
  in his pocket.” And this belief is also justified. You go
  home, but the telephone rings. They tell you that
  they have hired you for the job. It just so happens
  that you have fifty cents in your pants pocket. So
  your belief that the person hired for the job has fifty
  cents in his pocket was a justified true belief. But we
  couldn’t say that you had knowledge, could we?
      Epistemic Justification
 What can we know and how much do we know?
  To help answer these questions, we need a
  theory of epistemic justification. Knowledge is
  justified true belief. If we can determine when
  and how our beliefs are justified, then we can
  determine the scope and limits of our
  knowledge. In broad strokes, there are three
  main theories about epistemic justification:
 (1) Skepticism
 (2) Empiricism
 (3) Rationalism
 Skepticism says that there is no adequate
  justification for our beliefs, so we can never attain
  knowledge. We can have beliefs, but no knowledge.
 Global Skepticism denies that there can be
  knowledge of any kind about any subject matter.
  Not many people hold global skepticism, but it is
  hard to defeat in conversation
 Local Skepticism denies that we can have
  knowledge regarding some subject matters, but not
  all, or that some methods of justification are not
  reliable (like reading fortune cookies, astrology,
  psychic hotlines, alternative medicine, or TV news).
 An empiricist holds that our beliefs can be best
  justified in light of the evidence we receive from
  our senses. We therefore can know something if
  we can justify it with respect to what we see,
  hear, and feel about the world. According to
  empiricism, natural sciences like physics,
  chemistry, and biology produce the most reliable
  knowledge. We can know something if we can
  justify it through what we can experience
  through our senses.
 Criticism of rationalism
   Necessary truths are just tautologies (true by
    definition or true analytically or true in virtue of
    logical form) and don’t say much about the
   Rationalists produce absurd metaphysical
    claims about reality because they go too far
    and end up making bogus a priori claims that
    are also synthetic in order to say something
    meaningful about the world.
   John Locke (1632-1704)
   Bishop Berkeley (1685-1753)
   David Hume (1711-1776)
   John Stuart Mill (1806-1873)
   Bertrand Russell (1872-1970)
   Logical Positivists: A.J. Ayer (1910-1989)
   William James (1842-1910)
 A rationalist believes that our beliefs can
  be best justified in light of rational
  evidence, not sensory evidence. We can
  know something if it appears true in the
  light of reason, not our senses. According
  to rationalism, mathematics and logic
  provide the most reliable knowledge.
   Plato
   Rene Descartes (1556-1650)
   Baruch Spinoza (1632-1677)
   Gottfried Leibniz (1646-1716)
 The non-physical world of the Forms is
 The physical world is more like an illusion.
Rationalism: Descartes’ Meditations
 Purpose: He wants to find a certain and
  indubitable (beyond doubt) foundation on
  which to build all scientific knowledge.
 All knowledge must be based on:
   Intuition: The mind can grasp clear and
    distinct ideas with certainty.
   Deduction: Using deduction, one can derive
    new truths from other truths that are known to
    be true by intuition.
 http://frank.mtsu.edu/~rbombard/RB/Spino
 Empiricists believe that knowledge is
  acquired through sense experience.
 So there has to be some theory of
  perception that connects sense
  experience with reality:
   Whenever I perceive that object S has
    property P, S really has P.
      Empiricism: 3 Theories of
 Direct Realism (Naïve Realism)
 Representative Realism
 Idealism
   Empiricism: Naïve Realism
 Naïve Realism: What you see is what you
  get. When I perceive that object S has
  property P, S really has property P.
    Objection to Naïve Realism
 It is not always the case that what I see is the
  truth. There is a difference between appearance
  and reality, and sometimes appearances are
   Illusions and mirages
   People’s experiences differ: a wind may feel cold to
    me but warm to you. Who is correct?
   The buckets-of-water example: Rest one hand in
    freezing water and one in hot water. Take both hands
    out and put them into a bucket of warm water. The
    water in the bucket will feel hot to the cold hand and
    cold to the hot hand. Which hand is giving the correct
 Empiricism: Representationalism
 Representationalism: Our ideas (which
  come from sense experience) are
  representations of the external world.
  There is a difference between appearance
  and reality, and we do not directly
  experience reality. We only directly
  perceive our sense impressions. Some of
  what we experience is in reality.
 John Locke: Theory of knowledge
     and Representationalism
 We are born with minds that are like blank
  slates. There are no innate ideas. The view that
  there are innate ideas is dangerous and can be
  used to control people.

 There are two sources of ideas: (1) sensation
  (sense experience of sense objects) and (2)

 The ideas of reflection are produced from the
  mind’s working on the ideas of sensation:
  perceiving, doubting, thinking, believing,
  reasoning, knowing, willing.
        Locke: Knowledge and
 There are two kinds of ideas: (1) simple
  and (2) complex.
 Simple ideas are those like the idea of the
  color yellow (from sensation) or the idea of
  pain (from reflection) that cannot be
  broken down into other ideas.
 Complex ideas are made up of simple
  ideas. The mind can put simple ideas
  together to make a complex idea, like the
  idea of a golden mountain.
       Locke: Knowledge and
 The mind creates complex ideas, The
 (1) joins ideas
 (2) brings them together to compare them
 (3) abstracts (abstract the idea of “man”
  from my experiences of John and Harry.)
 Representationalism: Primary and
       Secondary Qualities
 There are two kinds of qualities. A quality is the
  power in an object to produce any idea in my
 Primary qualities are those that really do exist in
  the bodies themselves. These include: Shape,
  Solidity, Extension, Motion or Rest, Number
 Secondary qualities are those that do not really
  exist in the bodies themselves. These include:
  Tastes, Colors, Sounds, Odors, and certain
  Feelings of Touch, like softness or roughness.
         Locke: Substance
 Qualities do not just float around. They
  have to be in something. Something has to
  hold them together and organize them.
  The power to produce ideas in my mind
  has to be in something. This something is
  substance, which Locke takes to be
 Substance is matter, but we cannot say
  what it is because we never perceive it.
     Bishop Berkeley: Idealism
 Berkeley argues that if we are true
  empiricists, then we have to reject Locke’s
  idea of substance, or matter, because it is
  never perceived. Matter is a meaningless
 Berkeley argues that there is no mind-
  independent substance. The existence of
  anything depends on a perceiving mind.
 “Esse Est Percipi” – To be is to be
  perceived (by a mind).
            Berkeley: Idealism
 Rejects Locke’s distinction between primary and
  secondary qualities. There are no mind-
  independent qualities, no-primary qualities.
  Every quality is like a secondary quality. Every
  quality is experienced through a perceiving
  mind. Only sensed qualities are real.
 “In truth, the object and the sensation are the
  same thing, and cannot therefore be abstracted
  from each other.”
 Locke had removed beauty (and other
  secondary qualities) from the world. This made
  the world ugly.
         Berkeley: Idealism
 If the object is the same thing as the
  sensation, then this beings up the problem
  that we return to a kind of naïve realism.
  What we see is what we get. There seems
  to be no basis for the distinction between
  appearance and reality. Our ideas do not
  represent an external mind-independent
  world that we can be mistaken about.
          Berkeley: Idealism
 Another problem is that it seems that for
  anything to exist, it has to be perceived by
  a mind. But if a tree falls in the woods and
  no one is there to hear it, does it make a
 If we all close our eyes, does the world
          Berkeley: Idealism

 So What is the cause of our ideas if not
  the power in some mind-independent
  material substance to produce ideas in our
  minds? What keeps our ideas together?
         Berkeley: Idealism
 God is the source of our ideas. God is the
  mind that perceives all things. God is the
  (spiritual) substance behind all things.
 God sees the tree fall, so it does make a
 Berkeley finds room for non-physical
  spiritual beings and rejects Locke’s
  materialism which seems to lead to
    Berkeley’s Instrumentalism
 The abstract ideas of scientists, like the ideas of
  force, attraction, and gravity, do not refer to
  anything real. Only sensed qualities exist. There
  is nothing other than what we can perceive. But
  these ideas are still useful ideas that can help us
  explain things. They just do not refer to anything
 There is no causality. We never see that. Things
  just follow each other in time: A follows B, but it
  is never possible to say that A is the cause of B.
 God orders the behavior of all things.
         Hume: Empiricism
 Explaining a similar empiricist view, Hume
  distinguished between (1) impressions and
  (2) ideas
 Every idea comes from some impression
  from sense experience.
          Hume: Empiricism
 If a term has any meaning, then it must be
  connected to an idea derived from some
  sense impression. If it is not, then the term
  is meaningless.
 Hume: Empiricism and Skepticism
 Hume thinks that if we are strict empiricists, then
  we have to be skeptical about many things. We
  cannot know much about the following:
 External World
 Substance
 Self
 Causality
 God
 Ethics
 Standard of Beauty
           Theories of Truth
 Correspondence Theory
   A belief is true if it corresponds to some
    fact or real object
 Coherence Theory
   A belief is true if it coheres with a body of
    other statements that we take to be true
 Pragmatic theory
   A belief is true if it works for you. It helps
    you understand things and leads you to
     Correspondence Theory
 Plato: Truth is obtained by grasping the
 Logical Positivists: A.J. Ayer

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