1.4 Validity, Truth, Soundness, Strength and Cogency Learn...
Transcript of 1.4 Validity, Truth, Soundness, Strength and Cogency Learn...
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1.4 Validity, Truth, Soundness, Strength and Cogency
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: It is 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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❖ 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}