Faulty Logic

Examples of truly logical thinking and writing are not easy to come by in the age of "infotainment." In fact, you have likely seen and heard so much bad logic by now you probably have what Ernest Hemingway called a "crap detector" in your head, even if you do not know the correct term for each logical error (or "fallacy") you detect. Here is a list of persuasive statements and assertions which violate some of the basic laws of logic. As you read each example, decide why the reasoning is fallacious - then read the analysis, which provides a lofty and intellectual-sounding handle you can use to expose your opponent's faulty logic. So, in the spirit of Hemingway, crush some tinfoil on your built-in "crap detector" antennae and read on!

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1. Podunk Community College should not require a freshman writing course. Harvard does not require a freshman writing course and the students there get along just fine without it.

False Analogy. It is false because the two items do not have strong enough similarities to predict that what happens in one will happen in the other.

2. Everyone wants to get married someday. A good self-concept is important in attracting a husband or wife. Therefore, everyone should develop a good self-concept.

False Premise. This example starts a logical statement with an assumption that is false; not everybody wants to get married. So even if the conclusion drawn is valid, the argument it is built on is not.

3. Suds 'n Spuds is a great restaurant: you can see how shining clean the kitchens are!

Distraction or "Red Herring." This example distracts the audience from far more important criteria used to establish whether or not a restaurant is good. Even if - to invent a name - Monsieur Taco has a shining clean kitchen, it might well be a lousy restaurant with horrible food and an awful waitstaff!

4. Ms. Bauer is an incompetent math teacher. She always wears blue jeans.

Ad hominem. "Against the person." Instead of evaluating any faults in teaching technique/theory/pedagogy, it calls attention to things about the teacher as a person which are UTTERLY unrelated to her performance and abilities.

5. Ms. Bauer is an incompetent math teacher. She's a wild-eyed radical in her educational theories.

Name-Calling and Genetic Fallacy. Similar to (but different from) ad hominem, the submission that Ms. Bauer's ideas have their background in radicalism - and are therefore supposedly suspicious - illustrates the genetic fallacy: defamation of a person or ideas purely on the basis of their background (not just an opinion: "Rush Limbaugh is a big, fat idiot" is therefore an ad hominem). Another example of the Name-Calling and Genetic Fallacy: "I'm not surprised Al is in trouble. His father did a stretch in jail, you know."

6. Look at this fourteen-year-old child who has run away from home to hide her shame ... pregnant, unwashed, friendless, penniless, at the mercy of our social service agencies. Can you still claim that sex education should be taught in high school?

Appeal to Pity. Tear-jerking description. Question is posed so disagreement would appear heartless. Similar to (yet different from) Red Herring, above.

7. Suds 'n Spuds is a great restaurant; no one has reported someone dying of poisoning yet!

Appeal to Ignorance. Your argument on something is supposedly true because its opposite has not been proven true. ("See that door move on its own?! Zoinks! GHOSTS! Run, Scooby!") Similarly, absence of evidence is not evidence of absence.

8. Either we continue to build nuclear weapons or we will fall prey to the Russians (or Taliban or Chinese or Iraqis or whomever).

Either/Or Fallacy. Writer pretends only two choices exist.

9. It has been proven that all heroin addicts smoked marijuana in their youth. Therefore, smoking marijuana leads to heroin addiction.

Post hoc, ergo propter hoc. "After this, therefore because of this." Heroin addicts probably really started on mother's milk; does it lead to heroin? Other examples: "The cock crows, then the sun comes up, therefore the cock is responsible for raising the sun every morning" and "President Reagan's peacetime military buildup - for which we're all still paying - led to the fall of Communism."

10. All the teenagers who like alternative rock music display little enthusiasm for school and have dirty feet and pierced noses. Therefore, alternative rock leads to dirty feet, pierced noses, and lack of enthusiasm in school.

Concurrence Fallacy. Two things happening at the same time need not indicate a causal relationship. Some may say the country started "going downhill" since prayer was taken out of schools, which concurs with the NFL's playing football on artificial turf; perhaps neither has anything to do with this perception of "going downhill." The rooster's crowing when the sun rose caused it to come up? Nope. Difference from post hoc, ergo propter hoc is only one of timing; post hoc is "after the fact," concurrence is during.

11. History tells us idealistic leaders are never effective.

Personified Abstraction. History is personified because it is supposedly talking, but the writer can make it say anything he or she wants it to. History "tells" us nothing.

12. I don't have any children, but I take my niece and my neighbor's child to the zoo and the park every week or so. I can tell children really love me.

Ill-Founded Generalization. Conclusion is based on insufficient evidence. Whenever you draw a conclusion you are making an inductive leap when you feel you have sufficient evidence. Look before you leap! If 4 of 20 students in your WRA135 section wear glasses, you may NOT generalize to say "20% of all WRA135 students require corrective lenses."

13. Students who take earth science instead of physics are lazy. Susie took earth science instead of physics. Lazy Susie should be kicked out of school.

Non Sequitur. "It does not follow." Even if we were to believe the premise ("students who take earth science instead of physics are lazy"), there is nothing in the line of reasoning that indicates lazy students should be kicked out of school; let poor Susie alone!

14. Juan is an impressive speaker because he always touches his listeners deeply.

Circular Reasoning or "Tautological Reasoning." The very meaning of "impressive" includes the idea of touching someone deeply - intellectually or emotionally. In an argument this is ineffective and absurd, just as "he is handsome because he is good looking" would be.

15. Essay exams should be abolished because they require writing skills.

Begging the Question. Essay exams are supposed to require writing skills in order to be essay exams. Hidden premise: writing skills should not be required of students.

16. Prof. Drake says, "All students turn their papers in on time." Rachel says, "But I'm a student and I turn my papers in late." Mean Old Drake says, "Then you're not really a student."

Equivocation. The original premise is true only of ideal students. Don't let Drake change the definition of "student" on you, Rachel! (But get your papers in on time, daggoneit!)

17. My Political Science professor says "new math" is impossible for students to learn.

Appeal to Wrong Authority. While, indeed, sometimes X=X plain-and-simple, "PoliSci" pedagogy does NOT equal "new math" pedagogy! Another example might be "according to REM's Michael Stipe, only 'silly' people think Windows NT is a better multi-tasking and networking operating system environment than Macintosh X." Computer operating platforms is NOT his area of authority! NOT to be confused with False Premise, above.

18. No, you vegans cannot order a bacon, lettuce, and tomato sandwich with peanut butter instead of bacon! Then everyone would start wanting substitutions on their BLT sandwiches.

Slippery Slope. One instance will inevitably lead to many more? NOT necessarily so!


Test your skills on these "scientific" bits of logic!

last updated: 11.9.01