Lesson 1 - Arguments

Sound argument a valid argument with all true

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Sound argument = a valid argument with ALL true premises. P1. If George Washington was our first president, then he served before President John Adams. P2. GW was our first president. Evaluating arguments

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1/25/11 Two steps to evaluation: Test argument for validity – can the conclusion still be false even if all the premises were true? Test for soundness – are all the premises in fact true? Must be done in steps: P1. All tigers are mammals. P2. All cats are mammals. C. Therefore, all tigers are cats. Validity is a result of logical form P1. All x’s are y’s Evaluating arguments {B90D1376-8997-4BD4-9C91-7884B55086B3} Valid Sound {E8C4B64C-DE00-4FC9-B724-28F43A4A705C} {D585994F-9BD3-4AB6-B679-E239C8BFB78C} {91B7C904-0209-4103-A8DB-489DC0A4DE12}
1/25/11 Modus ponens (conditional reasoning): P1. If a is true, then b is true. P2. a is true. C. Therefore, b is true. Modus tollens (more conditional reasoning): P1. If a is true, then b is true. P2. b is not true. C. Therefore, a is not true. Universal membership: P1. All a are b. P2. x is an a. Valid forms of inference

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1/25/11 “Virginia Tech will win the National title this year, because they have the best defense, and defense wins championships.” P1. The team with the best defense will win the championship.
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