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Unformatted text preview: Wednesday, May 13 Today, we embark on Symbollic Logic. So... tro to Symbollic Logic Intro to Symbollic Logic 8.2 Symbols for Conjunction, Negation, and Disjunction 8.3 Conditional Statements and Material Implication 8.4 Argument Forms and Refutation by Logical Analogy 8.5 The Precise Meaning of “Invalid” and “Valid” 8.6 Testing Argument Validity Using Truth Tables ...and so on. Quick Review ● Yesterday we talked about logical fallacies, which are patterns of reasoning that are problematic, but that can deceive us, even when we're on our toes. ● We talked about Fallacies of Relevance (appeal to emotion, red herring, straw man, ad hominem/tu quoque, appeal to force, missing the point), where the premises don't connect to the conclusion. ● We talked about Fallacies of Defective Induction (argument from ignorance, appeal to inappropriate authority, false cause, and hasty generalization), where the premises are relevant, but too weak to support the conclusion. ● We talked about Fallacies of Presumption (accident, complex question, and egging the question), where the premises assume too much. begging the question), where the premises assume too much. ● We also talked about Fallacies of Ambiguity (equivocation, amphiboly, accent, composition and division), where there is an ambiguity or equivocation in the use of a word or phrase. Intro to Symbolic Logic ● Symbolic Logic is a tool for analyzing whether or not the conclusion of an argument follows necessarily from the remises of the argument. Symbolic Logic is thus a tool for premises of the argument. Symbolic Logic is thus a tool for determining whether or not an argument is valid. ● Consequently, Symbolic Logic is only useful for deductive arguments. ● In the same way that we can identify fallacies, which are relationships between premises and conclusions that we know to be invalid, we can identify certain relationships etween premises and conclusion that we know to be valid. between premises and conclusion that we know to be valid. ● Remember, of course, that validity is just a relationship between the premises and the conclusion, such that i f a l l t h e p r e m i s e s a r e t r u e , t h e n t h e c o n c l u s i o n m u s t b e t r u e ( n o t n e c e s s a r i l y t h a t t h e p r e m i s e s a r e a l l t r u e ) . Intro to Symbolic Logic (con't) ● Consider the following: it is raining, the streets will be wet. If it is raining, the streets will be wet. It is raining Therefore, the streets will be wet. If I am Elvis, then you are all space aliens. I am, in fact, Elvis. Thus, you are all space aliens. Intro to Symbolic Logic (con't) ● Note that all of the above are valid. It looks like there is a pattern here: If [x], then [y]....
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 Spring '09
 lwonard

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