lecture20 - Lecture 20 Argument Forms of Propositional...

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Lecture 20 Argument Forms of Propositional Logic Patrick Maher Philosophy 102 Spring 2009
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Review Operator Meaning not · and or if . . . then if and only if
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Definitions We used upper case letters ( A , B , . . . ) to represent simple statements. We will use lower case letters ( p , q , . . . ) as statement variables , which stand for any arbitrary statement. An argument form is an arrangement of statement variables and operators that becomes an argument when statements are uniformly substituted for the statement variables. A substitution instance of an argument form is an argument obtained by uniformly substituting statements for statement variables in the form. An argument form is valid if all substitution instances of that form are valid.
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Disjunctive syllogism p q p q This is a valid form. Example Either I will become a doctor or I will become a biochemist. But I will not become a doctor. Therefore, I will become a biochemist. D B D B
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These forms are invalid p q p q p q p q
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Pure hypothetical syllogism p q q r p r This is a valid form. Example
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This note was uploaded on 04/13/2009 for the course PHIL 102 taught by Professor Weinberg during the Spring '08 term at University of Illinois at Urbana–Champaign.

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lecture20 - Lecture 20 Argument Forms of Propositional...

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