1.4 Validity, Truth, Soundness, Strength and Cogency

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1.4 Validity, Truth, Soundness, Strength and
Cogency

• Goal Learn the terms used to evaluate inductive
  and deductive arguments

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Deductive Arguments

• An argument in which it is claimed that it is
  impossible for the conclusion to be false if the
  premises are true is a deductive argument.
• That is, it is claimed that the argument it
  valid.
• In a valid argument, if the premises are true,
  the conclusion must be true too.

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• Validity describes the relationship that the
  premises bear to the conclusion in a deductive
  argument.
• The test for validity Imagine that the premises
  are true and the conclusion is false

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• If you cannot imagine that the premises are true
  and the conclusion is false, then the argument is
  VALID.
• If you can imagine that the premises are true and
  the conclusion is false then the argument is
  INVALID.

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• P1. All CCU students are hardworking.
• P2. Howie is a CCU student.
• C. So, Howie is hardworking.
• Valid if the premises were true, the conclusion
  could not be false.

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• P1. All CCU students are hardworking.
• P2. Howie is hardworking.
• C. So, Howie is a CCU student.
• Invalid if the premises were true, the
  conclusion could still be false.

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• In a good argument the premises support the
  conclusion (validity) AND the premises are true.
• A good deductive argument is called a sound
  argument. A sound argument is valid and has all
  true premises.

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• P1. All CCU students are hardworking.
• P2. Howie is a CCU student.
• C. So, Howie is hardworking.
• Valid if the premises were true, the conclusion
  could not be false.
• False premise(s)
• Unsound

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Sound Valid True Premises

• P1. If Obama is president then he is Commander in
  Chief.
• P2. Obama is president.
• C. Therefore, he is Commander in Chief.
• Is this argument sound?

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Sound Valid True Premises

• P1. All cats have tails.
• P2. My dog has a tail.
• C. So, my dog is a cat.
• Is this argument sound?

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Inductive Arguments

• An argument in which it is claimed that it is
  improbably that the conclusion is false if the
  premises are true is an inductive argument.
• That is, it is claimed that the argument is
  strong.
• A strong argument is one whose conclusion is
  probably true given the truth of the premises.

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• The test for strength Imagine the premises are
  true, and determine whether the conclusion is
  probable given the truth of the premises.
• Does the truth of the premises make it more like
  that the conclusion is true then had the premises
  been false?

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• P1. All past presidents have been men.
• C. The next president will be a man.
• Inductive Possible for the conclusion to be
  false
• Can be made stronger or weaker given more
  information.
• There are degrees of strength!

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• P1. All past presidents have been men.
• C. The next president will be a man.
• P1. All past presidents have been women.
• C. The next president will be a woman.

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• P1. Every student I know has a cell phone.
• C. So, all students have cell phones.
• P1. Every only child surveyed reported being
  satisfied not having siblings.
• C. Thus all only children are so satisfied.

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Cogent Strong True Premises

• P1. I have lost every hand so far.
• C. So, I will win the next hand.
• P1. Korby Ray used Ultra 90 and lost 50.
• C. So, if I use Ultra 90 I will lose 50.

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• Arguments Premises conclusions
• Factual claim (are the premises true?)
• Inferential claim (is the argument
  valid/strong?)
• Deductive Arguments
• Sound Valid True premises
• valid if the premises are true, the conclusion
  must be true
• Inductive Arguments
• Cogent Strong True Premises
• strong the conclusion is probably true if the
  premises are true

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Deductive Arguments

• 1. All hamburgers are high in fat.
  Quarter-pounders with cheese are hamburgers.
  Therefore, quarter-pounders with cheese are high
  in fat.
• Sound ___ Valid ___ True premises ___

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Deductive Arguments

• 1. All hamburgers are high in fat.
  Quarter-pounders with cheese are hamburgers.
  Therefore, quarter-pounders with cheese are high
  in fat.
• Sound _ ? __ Valid __?_ True premises _ ? __

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• 2. All hamburgers are high in fat. Chicken
  nuggets are high in fat. Therefore, chicken
  nuggets are hamburgers.
• Sound ___ Valid ___ True premises ___

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• 2. All hamburgers are high in fat. Chicken
  nuggets are high in fat. Therefore, chicken
  nuggets are hamburgers.
• Sound _x__ Valid __x_ True premises _ ? __

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• 3. All hamburgers are good sources of vitamins.
  Fresh vegetables and fruit are hamburgers.
  Therefore, fresh vegetables and fruit are good
  sources of vitamins.
• Sound ___ Valid ___ True premises ___

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• 3. All hamburgers are good sources of vitamins.
  Fresh vegetables and fruit are hamburgers.
  Therefore, fresh vegetables and fruit are good
  sources of vitamins.
• Sound _x__ Valid _ ? __ True premises _x__

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Inductive Arguments

• Meatpacking has become the most hazardous
  occupation in the US, with three times the injury
  rate of factory work. Therefore, John who works
  at a meatpacking plant will probably get injured
  on the job.
• Cogent___ Strong ___ True Premises ___

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• 2. I havent gotten sick from eating fast food
  yet, so I will probably get sick if I eat fast
  food any time soon.
• Cogent___ Strong ___ True Premises ___

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• 3. McDs promises, to use only fresh, wholesome
  ingredients when serving you and your family so
  they only use fresh, wholesome ingredients in
  their food.
• Cogent___ Strong ___ True Premises ___

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• 4. Because McDs is the single largest purchaser
  of US beef, they have considerable say over how
  beef is processed in this country. So, the beef
  they buy (and sell) is safe.
• Cogent___ Strong ___ True Premises ___

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• 5. McDs webpage has a statement from Dr. Dean
  Ornish whose diet has been proven to reduce heart
  disease therefore, the foods that McDs serves
  are part of a heart-healthy diet.
• Cogent___ Strong ___ True Premises ___