Introduction to Ethics Lecture 2 A deeper look at arguments

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Introduction to EthicsLecture 2A deeper look at
arguments

• By David Kelsey

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Conclusions as premises

• Conclusions as premises
• The Margaret example (example 1),
• 1) Every student who made 90 percent or better on
  the midterms already has an A.
• 2) Margaret made a 94 percent on the midterms.
• Thus, 3) Margaret already has an A.
• 1) Margaret already has an A.
• 2) All students who have an A are excused from
  the final exam.
• Thus, 3) Margaret is excused from the final exam.

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Unstated Conclusions

• Unstated Conclusions
• Conclusions that are entailed by the words of the
  text.
• The Republicans example (example 2)
• 1) The political party that best reflects
  mainstream opinion will win the most seats in
  congress.
• 2) The republicans certainly best reflect
  mainstream opinion.
• What is the unstated conclusion?

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IndependentPremises

• Independent premises independently support the
  conclusion of an argument.

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The speed limit example

• An argument with independent premises
• Speed limit example (example 3)
• 1) Raising the speed limit will wear out the
  highways faster.
• 2) Raising the speed limit will result in more
  highway deaths.
• Thus, 3) We should not raise the speed limit.
• 2 arguments

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Dependent Premises

• Dependent premises support the conclusion of an
  argument only with the help of some other
  premise.
• Example Socrates is mortal
• Question What if a dependent premise is false?

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Good arguments

• A good argument
• The premises both support its conclusion and are
  reasonable
• Reasonable?
• Requisite Support?

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Valid arguments

• Valid arguments
• Necessary connection between premises and
  conclusion
• The premises entail the conclusion

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Valid arguments false premises false
conclusions

• We can have a valid argument with a false premise
  and a false conclusion.
• George Bush example (example 5)
• 1) George Bush is a robot.
• 2) If George Bush is a robot then he isnt the
  president.
• Thus, 3) George Bush isnt president.
• And we can have a valid argument with false
  premises and a true conclusion
• The moon is made of green cheese example (example
  6)
• 1) The moon is made of green cheese.
• 2) All things made of green cheese orbit the
  Earth.
• Thus, 3) The moon orbits the Earth.

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A validity metaphor

• Form
• Valid arguments have a certain form to them
• The link between premises and conclusion
• The puzzle metaphor

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2 more Validity tricks

• 2 more tricks
• Addition metaphor
• Imagine an argument as a mathematical problem of
  addition.
• Covering up the conclusion
• Cover up the conclusion and ask what do the
  premises entail?

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Sound Arguments

• A sound argument
• The Superbowl example (example 7)
• 1) The Ravens won the superbowl.
• 2) If a team loses a playoff game, then they
  dont win the superbowl.
• Thus, 3) The Ravens didnt lose a playoff game.
• Dreaming example (example 8)
• 1) Either I am in class right now or I am
  dreaming it.
• 2) I am in class right now.
• Thus, 3) I am not dreaming it.

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Strong Arguments

• A strong argument
• April showers example (example 9)
• 1) Every April we get some rain.
• Thus, 2) We will get some rain this April.

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Strong arguments false premises false
conclusions

• A strong argument with a false premise and a
  false conclusion
• Gravity example (example 10)
• 1) Every time I have ever dropped anything from
  my hand it floats up to the sky.
• Thus, 2) if I drop this pencil it will float up
  to the sky.
• A strong argument with true premises and a false
  conclusion.
• Swans example (11)
• 1) Every swan I have ever seen is white.
• Thus, 2) all swans are white.
• (All swans are not in fact white as there are
  black swans in Australia!)

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Cogent arguments

• A cogent argument
• 1.
• 2.
• The sun will rise set tomorrow (example 12)
• 1) Every day of my life the sun has risen in the
  morning and set in the evening.
• Thus, 2) Tomorrow the sun will rise in the
  morning and set in the evening.

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Deduction and Induction

• Deductive arguments
• valid or intended to be valid.
• Necessary conclusions
• Conclusions built out of premises
• Which of our 12 examples are deductive?

• Inductive arguments
• not valid.
• Strong?
• Likely conclusions
• Prediction
• Conclusion is new information
• Which of our 12 examples are inductive?

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Unstated Premises again

• How to identify the unstated premise
• Ask What must be assumed to make it either valid
  or strong?
• Add a general claim that connects the premises
  and conclusion
• Cheating example (12)
• 1) This is the second time you caught her
  cheating.
• 2) she shouldnt pass the class.
• This argument becomes valid when we add this
  premise
• 1.5)

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Determining the Unstated premise

• Now Ask Is the assumption reasonable?
• Yes or No?
• No, then determine what must be assumed to make
  the argument strong

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Unstated premises Strong arguments

• The bloodhound example (13)
• 1) Moores dog is a bloodhound.
• Thus, 2) Moores dog has a keen sense of smell.
• What do we need to add to make this argument
  valid?
• What do we need to add to make this argument
  strong?