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CHAPTER 4 SUMMARY
Common Forms
· Since argument forms are structures distinct from argument content, we can easily signify different forms by using letters to represent statements in the arguments. For example: If p, then q; p; Therefore, q. Some of the more common argument patterns that you encounter are like this pattern—they’re deductive, and they contain one or more conditional, or if-then, premises. The first statement in a conditional premise (the if part) is known as the antecedent. The second statement (the then part) is known as the consequent.
- There are several common patterns of valid conditional arguments: affirming the antecedent (modus ponens); denying the consequent (modus tollens); hypothetical syllogism (three conditional statements); disjunctive syllogism.
- There are two common patterns of invalid conditional arguments: affirming the consequent; denying the antecedent.
Reductio Ad Absurdum
One kind of powerful argument that you frequently encounter is known as reductio ad absurdum (reduction to absurdity). The idea behind it is that if the contradictory (negation) of a statement leads to an absurdity or falsehood, then the negation of the statement is false and the statement itself must be true.