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Lecture

Phil001 note5.doc

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Department
Philosophy
Course
PHIL 105
Professor
Kirstie
Semester
Winter

Description
#5 Rules of Argument Evaluation a) Conjunction: P and Q Aconjunction is true if and only if both conjuncts are true. It is false if either conjunct is false. Truth table P Q P and Q T T T T F F F T F F F F e.g. John is happy and Mary is happy Is false if: John is not happy or Mary is not Happy or John is not happy and Mary is not happy (neither John nor Mary is happy) b) Disjunction: P or Q Adisjunction is true if and only if at least one conjunct is true. It is false if and only if both conjuncts are false. Truth table P Q P or Q T T T T F T F T T F F F e.g.John is happy or Mary is happy is John is not happy and Mary is not happy (neither John nor Mary is happy) Inclusive Disjunctions It is false only when both disjuncts are false.(Table above) Exclusive Disjunctions P or Q but not both P and Q. Safe to choose an example where both disjuncts are false Disjunctions, and argument evaluation e.g. 1. Either Thor ate the steak or my flatmate ate it. 2. My flatmate didn’t ----- 3. Thor ate it. c) Conditionals Conditionals are ‘if….then’statements, conjoining 2 declarative sentences. 1) If Mike is studying, then he is in the library. Or 2) Mike is in the library if he is studying The sentence following ‘if’is the antecedent. The sentence following ‘then’is the consequent. P: Mike is studying Q: Mike is in the library Both 1) and 2) can be symbolized: If P then Q Which is equivalent to Q if P The conditional as a whole is false if and only if the antecedent is true and the consequent is false. Truth table P Q If P then Q T T T T F F F T T F F T Using the assignment above, this can also be symbolized If P then Q Which is equivalent to: P only if Q And Q if P. ‘if’announces the antecedent. ‘Only if’announces the consequent. d) Biconditionals Biconditionals are if and only if statements. j) John will get anAif and only if he studies hard. Truth table P Q P if and only ifQ T T T T F F F T F F F T Fallacies 1. Begging the Question Acircular argument commits the fallacy of begging the question. 2. The Straw Man fallacy e.g. 1. Valentine’s Day is exploited and overrated. ---------- 2. I don’t celebrate Valentine’s day. You would be committing the straw man falla
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