4/19/20091Chapter 11Evaluating InferencesSpring 2009San Francisco State UniversityInstructor Mike OlsenStatistical SyllogismsStandard FormN% of As are Bs.X is an A.Therefore, X is a B.99% of people who jump from the Golden Gate Bridge die.Jim is going to jump from the bridge.Thus, Jim will probably die from the jump.In arguments of this form, the inference will be of N% strength.An Example(1) 5% of all college graduates have taken calculus.(2) Mike is a college graduate.Therefore, (3) Mike has taken calculus.The inference is of 5% strength. In our terminology from Inductive evaluation, the inference is very weak.The Scope of Premises: “Some”•“Some” statements or conclusions are easy to prove and difficult to disproveExample:•Human beings once walked on the moon.–Easy to prove, difficult to disprove•Some men are mortal.–Easy to prove, difficult to disproveThe Scope of Premises: “All” Statements•When we make “All or None” statements, these are EASY to disprove, and hard to prove.•This is why you will see the Straw Man committed in this fashion.–All Roman Catholics are against abortion.–Bill Clinton has never visited Hong Kong.Logical Relationships: Consistency•Two statements (S1and S2) are consistent when it is logically possiblethat all of them are true.–Mike is over 30. Mike is over 20.•Any age over 30 would make both of these statements true.
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