GOOD REASONING

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GOOD REASONING

• Here are some examples of failures to reason
  well
• http//www.youtube.com/watch?vlj3iNxZ8Dwwfeature
  related
• http//www.youtube.com/watch?vuEP7uti0PDwfeature
  related
• http//www.youtube.com/watch?veZlaqNukjFY
• .

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ARGUMENT STRUCTURE

• Logic is the study of arguments.
• An argument is a sequence of statements
• - one is the conclusion to the others
• - all the others are premises.
• The premises provide evidence for the conclusion.

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EXAMPLES

• All humans are mortal.
• Jennifer Lopez is human.
• ?Jennifer Lopez is mortal.
• Sarah was not at the party.
• ? It couldnt have been Sarah that Jack was
  dancing with.

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FORMAL vs INFORMAL LOGIC

• Formal logic
• the study of argument forms
• abstract patterns common to many different
  arguments.
• valid invalid
• If P, then Q If P, then Q
• P Q
• ?Q ?P
• P and Q stand for any propositions.
• Informal logic
• the study of particular arguments in natural
  language

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PREMISES

• Premises and conclusions are always propositions
  (statements) they can be true or false.
• They are not questions, commands or exclamations.
• Test It is true/not true that P
• where P a premise or a conclusion

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EXAMPLE

• It is true that Sarah was not at the party.
• It is true that Where is Sarah?
• It is true that Dont you dare do that again!
• Note   
•    indicates that a statement is unacceptable

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NOTE 1

• At issue is the form of the statement,
• whether it CAN be true or false,
• not whether it IS true or false.
• These are PROPOSITIONS
• Snow is green.
• I am Jennifer Lopez.
• These are NOT
• What color is snow?
• Hey, look, theres JLo!

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NOTE 2

• Although the premises, by definition, provide
  evidence for
• the conclusion, this evidence may be good or not.
  
• You have to let me go to the party,
• everyone is going to be there.

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NOTE 3

• In standard form the conclusion appears at the
  end.
• In practice, the conclusion may appear anywhere.
• Jack could not have been the murderer.
• The victim was shot from 40 feet away.
• Jack is a blind and paralyzed from the neck
  down.

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CONCLUSION INDICATORS

• Inference indicators -
• indicate the role of a proposition in an
  argument.
• Conclusion indicators
• There are no lights on, ______ no one is home.
• Therefore
• Thus
• Hence
• So
• For this reason
• Consequently
• It follows that
• Which proves/means that
• As a result

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PREMISE INDICATORS

• Premise indicators
• _____ there are no lights on, no one is home.
• For
• Since
• Because
• Assuming that
• Seeing that
• Granted that
• In view of the fact that
• Inasmuch as

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CAUTION

• Conclusion and premise indicators dont always
  indicate
• conclusions and premises
• It has been ages since I ate really good
  sushi.
• Shes so cute!
• EXERCISE
• Identify premise/conclusion indicators.
• Generate sentences in which premise and
  conclusion
• indicators are not used as indicators.

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COMPLEX ARGUMENTS

• Arguments may proceed in stages.
• The conclusion of one set of premises may become
  the premise of another conclusion.
• All rational numbers are expressible as a ratio
  of integers.
• Pi is not expressible as a ratio of integers.
• ?Pi is not a rational number
• Pi is a number
• ?There exists at least one nonrational number.
• Here, the first two statements are basic
  premises.
• The third, is a nonbasic premise or intermediate
  conclusion.
• EXERCISE Rewrite arguments in standard form.

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IMPLICIT STATEMENTS

• Sometimes arguments are not actually expressed
• or may be expressed incompletely.
• One of us will be cleaning the bird cage,
• and it wont be me.
• Implicit conclusion
• You will be cleaning the bird cage
• Alisha wears Birkenstocks, which proves that you
• dont have to be a tree-hugger to wear
  Birkenstocks.
• Implicit premise Alisha is not a tree-hugger.

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BIRKENSTOCKS TREE-HUGGERS

• Shoes Hippies

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NON-ARGUMENTS

• 1. Reports
• 2. Unsupported Assertions
• 3. Conditional Statements
• 4. Illustrations
• 5. Explanations

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REPORTS, ASSERTIONS

• Reports convey information.
• Unsupported assertions are statements of what a
  speaker
• or writer happens to believe.

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CONDITIONAL STATEMENTS

• Conditional statements (if-then statements)
• antecedent and consequent sometimes implcit
• Should it rain the picnic will be cancelled.
• Pete will graduate provided he passes calculus.
• may be parts of arguments,
• but are not themselves arguments

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ILLUSTRATIONS

• Illustrations
• provide examples of a claim but do not prove or
  support it.
• Many wildflowers are edible.
• For example, daisies and day lilies are
• delicious in salads.
• There are borderline cases between examples and
  evidence.
• Many of the worlds greatest musicians died at
  27. For example, Jim Morrison, Janis Joplin,
• Jimi Hendrix and Curt Cobain.

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EXPLANATIONS

• Explanations
• try to show why something is the case,
• not to prove that it is the case.
• The Titanic sank because it hit an iceberg.
  (EXPLANATION)
• Capital punishment should be abolished because
• innocent people may be mistakenly executed.
• (ARGUMENT)

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EXPLANATIONS 4 TESTS

• 1. The common knowledge test
• 2. The past-event test
• 3. The authors intent test
• 4. The Principle of Charity test

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COMMON KNOWLEDGE

• Is the explanandum (what is being explained) a
  matter of
• common knowledge?
• (Why would you try to prove something that is
  widely
• accepted as fact?)
• Many musicians die young because they live
  hard

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PAST EVENT

• Is the explanandum an event that occurred in the
  past?
• Mel flunked because he never went to class.

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AUTHORS INTENT

• Is the author trying . . .
• to provide evidence for accepting claim as true
• or
• to offer an account of why an event occurred or
• why something is as it is?
• Kevin is majoring in Political Science because
• he wants to go to law school.

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PRINCIPLE OF CHARITY

• The Principle of charity requires that we
• interpret unclear passages generously.
• Here, that means not interpreting a passage as a
  bad argument
• when it would be reasonable to interpret it as a
  good
• explanation.

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CAUTION

• Not foolproof.
• No single shooter could have shot as quickly and
  
• as accurately as Oswald is alleged to have done
  in the
• Kennedy assassination. Therefore Oswald was not
  the
• lone shooter.
• Exercise Identify arguments and explanations.