Informal fallacies
1 Informal Fallacies
Formal vs informal fallacies a fallacy is a defect in an argument other than its having false premises An informal fallacy is a defect in the content of an argument.(A formal fallacy is a defect in the structure of an argument. We have seen many valid rules of deduction Formal fallacies can be understood as a use of unacceptable rules
2 Formal Vs Informal Fallacies • A fallacy is a defect in an argument other than its having false premises. • An informal fallacy is a defect in the content of an argument. (A formal fallacy is a defect in the structure of an argument.) • We have seen many valid rules of deduction. Formal fallacies can be understood as a use of unacceptable rules
Examples of formal Fallacies 1. Affirming the consequent P→Q/Q∥/P
3 Examples of Formal Fallacies • 1. Affirming the consequent: • P Q / Q // P
2. Denying the antecedent P→Q/~P∥~Q
4 • 2. Denying the antecedent • P Q / ~P // ~Q
3. Commutation of conditionals P→Q∥Q→P
5 • 3. Commutation of conditionals: • P Q // Q P