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How To Argue Without Cheating I: A Few Common Fallacies Name: _____________________________________________________ How to Argue Without Cheating Arguing is fun. Whether it’s a persuasive essay, a formal debate, or an enthusiastic discussion with a parent over the precise moment at which the garbage should be removed, we humans like to argue. You probably argue at least once a day, if not twice, twenty, or a few hundred times. Generally, these arguments don’t seem to have much method. You say this, they say that, and you go back and forth until somebody storms away. Little do you suspect that underneath this chaos, there is (or should be) a structure. There are whole sciences devoted to making a good argument, and one of them, logic, gets down to the nitty-gritty of proving even a single point. I. A First Look At Logic In the world of logic, you can make a point (called the conclusion) by using two sentences called premises. Like so: premise: All dogs have a liver. premise: Froofi is a dog. conclusion: Therefore, Froofi has a liver. You may not be thrilled by this perky factoid, but in the world of logic, this syllogism is a slam dunk. It’s valid. If the two premises are true, the conclusion must be true. That’s the joy of logic. Of course, those premises do have to be true. If the syllogism is valid and the conclusion is actually true, the argument is sound. But how about this: All dogs have wings. Froofi is a dog. Therefore, Froofi has wings. If all dogs had wings, Froofi would have wings. The syllogism is valid. But dogs don’t have wings. So although the syllogism is valid, the conclusion is false. When the error is in the facts, not the logic, the argument is unsound. When the facts are right, but the logic isn’t, the syllogism has a fallacy. A fallacy is an error in an argument. Cheryl jumped inside the house. Then the house collapsed. Therefore, Cheryl made the house collapse. Let’s say that happened. The premises are true, but is the syllogism valid? No. Even if Cheryl is a bit overweight, it’s unlikely she caused the house to collapse. The syllogism is invalid. It’s fallacious (it has a fallacy). Your teacher won’t be happy. Nor will Cheryl. In this unit, you’ll learn a few common fallacies. 1 ©2004abcteach.com How To Argue Without Cheating I: A Few Common Fallacies Name: _____________________________________________________ Exercise A: Scrutinizing Syllogisms For each premise (the first two sentences), circle whether the facts are right (“fact”) or not (“error”). Then circle whether each syllogism is valid or invalid. Finally, circle whether each argument is sound or unsound. (Note that an invalid syllogism, like a factual error, makes the argument unsound.) If the argument is unsound because of a fallacy, write “fallacy” on the line. If it has one or more incorrect facts, write one corrected fact on the line. 1. Trees have roots. fact / error This maple is a tree. fact / error Therefore, this maple has roots. valid / invalid _____________________________________________________ sound / unsound 2. Birds can fly. fact / error Airplanes can fly. fact / error Therefore, airplanes are birds. valid / invalid _____________________________________________________ sound / unsound 3. Gravel is crushed rock. fact / error Some rocks are emeralds. fact / error Therefore, gravel is crushed emerald. valid / invalid _____________________________________________________ sound / unsound 4. All rain is wet. fact / error All rain is weather. fact / error Therefore, all weather is wet. valid / invalid _____________________________________________________ sound / unsound 5. Kangaroos have pouches. fact / error All pouches are made of denim. fact / error Therefore, kangaroos pouches are denim. valid / invalid _____________________________________________________ sound / unsound 6. Blood contains iron. fact / error This sword is iron. fact / error Therefore, this sword is made of blood.