I. Argument and debate is something most of us do every day. To be clear, by argument I don’t mean a quarrel or fight, the sort of argument where people get angry and call each other names. I mean argument in terms of debate, making a rational case for a certain point of view. If you learn to spot and avoid the most common fallacies, or mistakes in reasoning, you’ll be fooled less often and you’ll be a formidable opponent in any rational argument. These probably won’t help much in a quarrel, because people often loose their higher reasoning abilities when they’re too emotional.
An argument can be divided in to it’s premises and conclusions. The premises are the facts or opinions that people may agree on, and they support the conclusion of the argument.
Premise 1: Roses are red
Premise 2: Red is a color
Conclusion: Therefore roses are colored.
This is a valid deductive argument because the conclusion logically follows from the premises.
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II. Sometimes we make mistakes when we argue and here we’ll discuss the most common logical errors people make when debating. These are called informal fallacies.
Consider the comic. It’s pretty clear that penguins aren’t old TV shows even without considering the penguin’s argument, but what went wrong? Below is a list of fallacies.
1. Ad Hominem: Argument against the man. This is when you attack the arguer instead of the argument. E.g. An oil company executive argues that global warming isn’t occurring. Instead of attacking his argument, an ad hominem attack would say “he profits from oil, therefore his argument is wrong.” If Hitler argued that the sun rises in the East, would his facts be wrong just because he’s a bad guy? No. An argument still stands on its own regardless of who’s making it.
2. Ad Populum: Appealing to popular opinion to make your case. Peer pressure is extremely powerful, but it doesn’t make arguments correct. E.g. A large number of people think drilling for more oil will solve our energy problems, therefore it’s true. This ignores the fact that we’re consuming more energy than oil can provide, and many people thinking it’s so doesn’t make it true. Most people thought the Earth was flat at one point, this doesn’t make it true.
3. Appeal to Authority: the arguer insists their argument is correct because a well known person thinks this is the case. E.g. The universe is static because Einstein argued this point in his most successful papers. Modern observation tells us that this is not the case. The universe is expanding. (To be fair, Einstein later said this was his “greatest blunder.”)
4. Ad Ignorantiam: Argument from ignorance. X is true because we don’t know that it’s not true. E.g. 1. We don’t know what those lights in the sky are, therefore it’s an alien spacecraft. 2. We know so little about how the human brain works, therefore psychic powers exist. Conspiracy Theories often rely on this fallacy. The CIA must have killed JFK because we don’t know who really did it. George Bush caused 9-11 because there are some facts we can’t account for, therefore a given conspiracy theory is true. Not knowing something doesn’t make a possibility a fact.
5. Begging the question or circular reasoning: This is when the conclusion just repeats the premises though perhaps in a different way. A is B, because B is A. E.g. Freud said the unconscious controls our lives because we live much of our life unconsiously.
6. False Dichotomy: This fallacy assumes there are only two choices, and that by disproving one, you’ve proven the other. E.g. You have to cut spending to pay off a debt. Therefore if you don’t cut spending you can’t pay off a debt. This is a false choice, it ignores other choices like increasing your income, or making tradeoffs to increase value.
7. Hasty Generalization: We commit this fallacy when we generalize something based on too small a sample size or something that is misleadingly vivid. E.g. 1. Driving in cars is safer than flying because you hear more about plane crashes than you do about car crashes. 2. This slot machine is lucky. I just put one coin in and I already won, so I’ll play it some more.
8. Post Hoc / False Cause: This assumes correlation is the same as causation. Many superstitions are based on this fallacy. E.g. 1. I broke a mirror and then had bad things happen, therefore breaking mirrors cause bad luck. 2. The economy crashed after the new policy, therefore the new policy caused the crash.
9. Irrelevant Conclusion / Missing the point: The argument says it’s proving one point, but it’s premises don’t actually support the conclusion. E.g. We need to hire more women because sexism is bad. Both of these may be true, but it doesn’t logically follow that hiring more women will end discrimination, it’s simply saying that sexism is bad.
10. Straw Man: This is when the arguer will attack a weaker or distorted argument creating the illusion that they’re disproving the point in question. E.g. A: Teens need to learn about birth control and sex education to prevent unwanted pregnancy and reduce abortion. B: You want children to have birth control and teach them to have more sex. You want to teach them that sexual activity has no consequences. B is committing the straw man fallacy. A is not arguing what B says he is.
11. Slippery Slope: If you start on a certain path then you will end up in the most extreme situation. E.g. A: The government should regulate air pollution. B: If you let the government control the air you breathe, then they’ll control what learn, read, eat and think. You’ll have a Stalinist state.
12. The Fallacy Fallacy: Premises can be true even in false arguments. Just because the conclusion is false, doesn’t mean the premises are too. This occurs a lot in areas where technical knowledge is important. Asking a lay person to defend something complex like climate change and then they fail to do so, is a common way people try to (fallaciously) disprove the argument. See he can’t make valid arguments for his case, therefore it’s all false. E.g. A: Abraham Lincoln was a great president because he ended the Great Depression. B. You’re wrong, he wasn’t even alive during the great depression. You don’t know what your’re talking about.The implication is that Lincoln wasn’t a great president. Lincoln can still considered a great president despite the fact that A didn’t know history very well and can’t make a valid argument.
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III. Sample Problem. Try to identify the fallacies in the following argument. There is one asterisk ( *) for each fallacy. So ** means there are two fallacies being committed. I’ll post the answers next week.
A. Marijuana should be legal because it grows from the Earth.*
B. You would think that being an ex-hippie an all.* I disagree. Drugs like marijuana and heroin cause more death and destruction than anything. Don’t you watch TV. It’s all over the news.*
A. Barack Obama, Bill Clinton, Steve Jobs, and John Lennon all smoked marijuana.* They were great leaders and artists. If people smoked more marijuana, we’d have more great people like this.*
B. If we legalized marijuana, then we’d have drug addicts all over the street. We’d have to pay for their bad habits and all of our children would become drug addicted losers. Do you want heroin addicts breaking into your house?* There are millions of chemicals in marijuana and we don’t know what they are. Pot smokers are probably killing themselves slowly .*
A. Do you really think marijuana is that bad? It’s the most used drug in the world after caffeine and alcohol, all of those people can’t be wrong.* People smoke pot because it makes them feel good, something that makes you feel good can’t be bad.*
B. Look, you can either legalize marijuana, sell it on the streets and in vending machines, or you can protect our children and keep this dangerous substance away from them.*
A. Well, I don’t think its so bad. I knew a guy who was very sick, and after he smoked he was all better.** Marijuana is used by cancer patients to help them through chemotherapy, and even George Washington grew cannabis. Do you think George Washington was a loser?*
B. That has nothing to do with it. Even if Washington grew hemp, there is no evidence that George Washington smoked pot, so your theory that marijuana is harmless is completely wrong.*
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Hanes Psychology 
November 30th, 2012 → 5:02 pm
[…] a science, philosophy, and debate background, I thought that if you could simply give a reasonable argument then the other party would see the light of your reason and be persuaded. Simply being right and […]