cr_thinking_9

cr_thinking_9 - Critical Thinking 9: Deductive Arguments...

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Critical Thinking 9: Deductive Arguments August 4, 2009 Kepa Korta kepa.korta@gmail.com
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Strong inductive argument The Gordon Street bridge is regularly inspected by qualified engineers Vehicles have been driving over it for years Therefore, it will be safe to drive over it tomorrow
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Defnition An argument is deductive if the truth of its premises guarantees the truth of the conclusion or if the premises are true the conclusion must be true or if the premises are true necessarily the conclusion is true or there is no possible world in which being the premise true the conclusion is false
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Deductive argument If you are under the age of 18, then you are legally a minor If you are legally a minor, then you cannot be sued Therefore, if you are under the age of 18, then you cannot be sued
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Another deductive argument If Sadie, lost her purse, then she lost her student ID card If she lost her student ID card, then she won’t be allowed to write her exams Therefore, if Sadie lost her purse, then she won’t be allowed to write her exams
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The form of the argument If p , then q If q, then r Therefore, if p then r
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Truth-functional statements Either I lost the keys, or they have been stolen Virginia got a job 20 years ago and now she became vice-president It is false that it is raining Tom believes that Shirley believes him
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Truth functional operators and truth-tables - Negation: not- p TRUE (1) FALSE (0) FALSE (0) TRUE (1) Not- p p
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Truth functional operators and truth-tables - Conjunction: p and q 0 1 0 0 0 0 0 1 q 0 1 1 1 p and q p
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cr_thinking_9 - Critical Thinking 9: Deductive Arguments...

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