Truth

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Truth
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What is truth?

• Semantic theory What does true mean?
• Accounts for inferences using true
• Target sentences (Tarski)
• Snow is white is true iff snow is white

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Paradoxes

• Liar One of themselves, a prophet of their own,
  said, "Cretans are always liars. . . ." (Titus
  112)
• Not really paradoxical
• Is it true or false?

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Cretans

• Cretan Everything a Cretan says is false.
• Suppose it is true.
• Then what this Cretan has said must be true.
• But then everything a Cretan says is false.
• Including that.
• So, it must be false.

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Cretans

• Cretan Everything a Cretan says is false.
• Suppose it is false.
• Then what this Cretan has said must be false.
• So, sometimes Cretans say true things.
• Thats possible the above just isnt an example
  of it.

Hes such a Cretan!
Everything a Cretan says is false
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Modern Liars

• Liar This sentence is false
• Strong liar This sentence isnt true
• Pairs (etc.)
• A Everything B says is true
• B Everything A says is false

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Philosophical theories of truth

• What makes true sentences true?
• By virtue of what are true sentences true?
• What do true sentences have in common?

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Correspondence Theory

• A sentence (or statement, or belief) is true iff
  it corresponds with reality
• iff, that is, it corresponds to some fact.
• It is false if there is no corresponding fact.

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Aristotles version

• To say of what is that it is not, or of what is
  not that it is, is false,
• while to say of what is that it is, and of what
  is not that it is not, is true

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Bivalence

• so that he who says of anything that it is, or
  that it is not, will say either what is true or
  what is false. . . .
• Aristotle here argues for bivalence
• Every statement is either true or false
• Classical logic maintains precisely that
• But it has been challenged

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Challenges to bivalence

• Vagueness
• Austin is large
• This course is hard
• Presupposition failure
• All Johns children are asleep
• The King of France is bald
• Eminem regrets sleeping with Bill Clinton
• Indeterminacy
• There will be a sea battle tomorrow
• Sherlock Holmes had three hats

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Challenges to correspondence

• Must the correspondence theorist maintain
  bivalence?
• Say S says that p
• Aristotle argues
• S is true iff p
• S is false iff not p
• Either p or not p law of excluded middle
• So, S is true or S is false
• One can deny excluded middle

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External standard

• The correspondence theory accounts for the
  dependence of truth on the external world.
• What makes it true that snow is white? The fact
  that snow is white.
• By virtue of what is it true that my cat is
  asleep? The fact that my cat is asleep.

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External standard

• The cat is on the mat

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Aquinas on Correspondence

• St. Thomas Aquinas (1224-1274) develops the
  correspondence theory.
• Truth is the goal of our intellectual activity.
• When we think about something, we want to know
  what is true of it.
• Truth is what thinking aims at.

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Intellect thing

• We call our belief true if it conforms to its
  object
• Truth the conformity of intellect and thing

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Aquinas on Truth

• To know something is to make your intellect
  conform to an object
• Your thought must be in some way similar to the
  object it is about
• It must agree with the way things are
• Your thought and the object must in some sense
  have the same form

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Picture Theory

• Later philosophers have sometimes interpreted
  this in terms of a picture theory
• Your thought is true iff it correctly depicts
  reality
• iff it is an accurate (though of course
  incomplete) picture of how things are
• The goal of thinking is thus to picture reality
  accurately,
• to come to have the same form as reality itself.

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Picture Theory

• The cat is on the mat

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Picture Theory
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Isomorphism

• A true belief has a form similar to what it is
  about
• It is isomorphic to some part or aspect of the
  world
• A true belief maps into the world
• Its content matches part of reality

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Russells Theory of Truth

• Bertrand Russell (1872-1970) defends the
  correspondence theory
• A belief is true iff there is a corresponding
  fact
• My belief that Charles I died on the scaffold is
  true iff its a fact that Charles I died on the
  scaffold

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Analytic philosophy

• A statement is true iff there is a corresponding
  fact
• So, the truth of a statement depends only on a
  part or aspect of the world the existence of a
  fact
• We can understand wholes in terms of parts
• The analytic method analyze wholes into parts

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Objections to the correspondence theory

• ? Independence Is its assumption of an
  independent reality justified?
• ? Informativeness Can we explain "facts" or
  "correspondence" without begging the question?

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Objections to the correspondence theory

• ? Modality Can we explain necessary or
  counterfactual truths, such as '7 5 12' or
  'The Red Sox would have won if Buckner had caught
  the ball? (To what do they correspond?)
• Interrelation Do the parts into which we analyze
  reality behave independently enough for us to
  investigate them independently?

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Coherence Theory

• A sentence or belief is true if it coheres with a
  comprehensive theory of the world
• Francis Herbert Bradley (1846-1924) decries facts
  as a "vicious abstraction."
• Holism explain parts in terms of wholes
• Explain things in terms of context, function

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Coherence

• We cannot evaluate knowledge claims apart from an
  entire system
• A true belief coheres with a maximally coherent
  and comprehensive system of beliefs
• So, to assess the truth of a belief, we must see
  how it fits with our best overall system
• We cannot evaluate beliefs one-by-one we must
  evaluate them in the context of a system

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The Web of Belief

• Experience

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Objections to Coherence

• Could there be more than one comprehensive and
  coherent system of beliefs?
• Coherence consistency can all be true
• But then coherence is defined in terms of truth
• Defining truth in terms of coherence would be
  circular
• What about the world?

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Pragmatism

• Charles Sanders Peirce (1839-1914) the pragmatic
  theory of truth.
• Principle of pragmatism There is no difference
  in meaning without a difference in practice.

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Pragmatism

• Meaning depends entirely on practice
• To get clear about the meanings of our terms and
  thoughts, we need to be clear about their
  practical antecedents and effects

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Scientific Inquiry

• Thought aims at truth. Not all practice does
• But scientific inquiry aims at truth
• It aims in particular at stable belief beliefs
  that will not have to be given up in the face of
  further information

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Defining truth

• The correspondence theorist defines scientific
  activity as that activity that aims at the truth
• Peirce defines the truth is that at which
  scientific activity aims

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Peirce on Truth

• The opinion which is fated to be ultimately
  agreed to by all who investigate, is what we mean
  by the truth, and the object represented in this
  opinion is the real.

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Limit of scientific inquiry

• Truth, then, is a kind of coherence (or, as
  Peirce prefers to call it, concordance)
• with the ideal limit of scientific inquiry
• The truth is what we all eventually are bound to
  agree on

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Belief Revision

• Science is a process of belief revision
• When we encounter new information and update our
  beliefs, we keep some, reject others, and add new
  ones
• Truth is what works in that context of belief
  revision
• Truth is that on which our process of belief
  revision stabilizes