Logical Arguments: Tactics and Fallacies

1. Argument Tactics • Correctly and incorrectly applied

2. About Logical Arguments Arguments are made up of premises and conclusions. Premise: If A is true, then B is true. Premise: A is true. Conclusion: Therefore, B is true.

3. About Logical Arguments An argument can be valid, but not sound. Valid: If boa constrictors bite their prey, it dies. A boa constrictor bit my dog; therefore, my dog is dead. Sound: If boa constrictors get ahold of their prey, they squeeze it to death. A boa constrictor got ahold of my dog; therefore, my dog is dead.

4. A Few Types of Arguments Ad Absurdum “Some argue that marijuana is a gateway drug to heroin and cocaine. Will popping Reeses Pieces lead to popping ecstasy?” -Caitlin Niman

5. A Few Types of Arguments Modus Ponens If A is true, then B is true. A is true; therefore, B is true. “If the dam broke, the valley would flood. The dam broke; therefore, the valley flooded.”

6. A Few Types of Arguments Obviously, this can be switched around and elaborated. If and only if A is true, then B is true. B is true; therefore, A is true. “If and only if the dam broke, the valley would flood. The valley has flooded; therefore, the dam broke.”

7. A Few Types of Arguments Argument by Analogy “Parents look out for their children; so, teachers should look out for their students.” “An argument, just like a house, needs a solid structure.”

8. A Few Types of Arguments Mentioning things by not mentioning them (This isn’t so much an argument as a tactic.) “I won’t even mention her clothes.” “There’s no need to recount the Senator’s past indiscretions.”

9. Some Logical Fallacies Post hoc ergo propter hoc: “After it, therefore because of it. “I only caught a cold after I shook hands with you.” “Kennedy was assassinated because the CIA failed to kill Castro.”

10. Some Logical Fallacies Ad hominem: “At the person” “I don’t think Sarah Palin’s qualified to be president.” “That’s because you’re sexist.” “It was just one dance!” “Only a man would say that.”

11. Some Logical Fallacies Begging the question Misused: “This new evidence begs the question of whether he can be trusted.” It actually looks like this: “O.J. Simpson did not kill his wife, because he is a world-class football player, not a murderer.”

12. Some Logical Fallacies The slippery slope “If we legalize gay marriage, the institution of marriage is going to deteriorate everywhere.” “If I let you do that, I have to let everyone do it.”

13. But, don’t be fooled: “fallacies” aren’t always fallacious.

14. Non-Fallacious Uses Post hoc ergo propter hoc: “After it, therefore because of it” “I only caught a cold after I shook hands with you.” “My computer only crashed after I dropped it.” “He only stole my bike after I broke his Xbox.”

15. Non-Fallacious Uses Ad hominem: “At the person” “I don’t think Sarah Palin’s qualified to be president.” “That’s because you’re sexist.” “The senator broke all of his campaign promises.” “Politicians always lie during campaigns.”

16. Non-Fallacious Uses The slippery slope “If we legalize gay marriage, the institution of marriage is going to deteriorate everywhere.” “If we set a precedent with this case, more extreme rulings will follow.”