Answer Syllogism: All good test scores mean good course grades. Samsa’s test scores are all good. Samsa gets good course grades. Conditional: If you get good test scores, then you get good course grades. Samsa gets good test scores. There- fore, he gets good course grades. How Deduction Can Be Misused In the next lesson, you will learn about specific ways in which deductive arguments are used incorrectly, whether negligently or deliberately. The better you become at spotting these “logical fallacies,”the less likely you will be to accept one as truth. Simply, a deductive argument is invalid for one of two possible reasons: either or both of the premises are invalid, or the wrong conclusion was reached even though the premises are valid. This example contains a premise that is not true: All Americans wear sneakers. (Major premise) Harold is an American. (Minor premise) Therefore, Harold wears sneakers. (Conclusion) Since all Americans do not wear sneakers, the major premise is not true. That makes the conclusion, and therefore the deductive argument itself, invalid. In this case, the wrong conclusion is reached: Many Americans wear sneakers. Harold is an American. Therefore, Harold wears sneakers. Note that by restating the invalid premise to make it valid, you have not made the conclusion true. Harold may or may not be in the group of “many” who wear sneakers. The conclusion makes an assumption that goes beyond the information contained in the premises. In Short Deductive reasoning takes two premises, which may be rules, laws, principles, or generalizations, and forms a conclusion based upon them. In order to be valid, a deductive argument must have premises that are true and a conclusion that logically follows from those premises, without trying to go beyond them. When you understand how these arguments work, you will know how to construct your own strong arguments.You will also avoid being influenced or persuaded by faulty deductive reasoning when you recognize it and see its flaws. – DEDUCTIVE REASONING– 98 ■ Find a deductive argument in print. Put it in the form of a diagram, listing the major premise, minor premise, and conclusion. Is it valid? If not, why? ■ The next time you need to persuade someone to do something, such as eat at your favorite restau- rant instead of theirs or see the movie you prefer, argue for your choice using deductive reasoning. Skill Building Until Next Time L ESSON 12 EXPLORED the characteristics of a valid deductive argument. You know that you need two premises which are true, and a conclusion that logically follows from them without assuming or inferring any information not contained in the premises.An invalid argument con- tains one or more errors. It might have a factual error, such as a premise that is not true, or a conclusion that is not supported by the premises. Or, it may contain an error in logic. This type of error is known as a fallacy. There are a number of logical fallacies that can occur in deductive arguments. There are four major logical fallacies: 1. Slippery Slope 2. False Dilemma 3. Circular Reasoning 4. Equivocation Each of these will be explained in detail in the next sections. LESSON Misusing Deductive Reasoning— Logical Fallacies LESSON SUMMARY In this lesson you will see how the relationship between deductive rea- soning and logic works, or does not work. This lesson explores four of the most common logical fallacies that make deductive reasoning fall apart. 13 99 The argument might have two true premises, and a conclusion that takes them to an extreme. This is known as the slippery slope fallacy. Or, it might be a false dilemma fallacy, which presents in its major premise just two options (“either-or”) when in reality there are others. In circular reasoning, also known as begging the question, there is just one premise, and the conclusion simply restates it in a slightly different form. And finally, equivocation uses a word twice, each time implying a different meaning of that word, or uses one word that could mean at least two different things. Arguments intended to convince or persuade may be believable to many listeners despite containing such fallacies, but they are still invalid. Recognizing these fal- lacies is sometimes difficult. But it is important to be able to do so to prevent being mislead, or persuaded by faulty logic. Slippery Slope In Lesson 12, we discussed conditionals, which are one of the ways in which a deductive argument may be framed. Conditionals use an “if-then” premise to lead to a conclusion (example: if you do not pay your elec- tric bill, then your power will be turned off). When a conditional contains a logical fallacy, it is called a slip- pery slope. In this type of fallacy, it is asserted that one event will or might happen, and then, inevitably, another, more serious or drastic, event will occur. The slippery slope does not explain how the first event leads to the other. Often, it leaves out a number of steps between the two events, without saying why they will simply be bypassed. The argument takes the following form: 1. Event A has/will/might occur. 2. Therefore, event B will inevitably occur. The slippery slope argument makes an oppo- nent’s argument seem more extreme. It says that event A will eventually lead to an extreme, unwanted event B. The argument infers that the only way to avoid event B is to not do event A, or even anything at all. The gun lobby uses the slippery slope all the time to argue against any type of gun control. They say that any small measure, such as registration or waiting periods to pur- chase firearms, will lead to drastic control, or even con- fiscation of their weapons. Here is another example: “We have to stop the tuition increase! Today, it’s $5,000; tomorrow, they will be charging $40,000 a semester!” Note that there are many possible steps between event A, the tuition increase, and event B, the charging of $40,000 a semester. An increase could occur every year for ten years or more before there was a jump from five to forty thousand dollars. In addition, tuition might never reach $40,000. This is a slippery slope because one tuition hike to $5,000 does not inevitably lead to a charge of $40,000. Other examples are listed below. Keep in mind the possible intermediate steps between event A and event B in each, and the likelihood, or unlikelihood, that B will ever be a result of A. ■ Don’t let him help you with that. The next thing you know, he will be running your life. ■ You can never give anyone a break. If you do, they will walk all over you. ■ This week, you want to stay out past your cur- few. If I let you stay out, next week you’ll be gone all night! – MISUSING DEDUCTIVE REASONING—LOGICAL FALLACIES– 100 Practice Rewrite the following argument to remove the slippery slope fallacy: We shouldn’t give military aid to other countries. The next thing you know, we will have thousands of troops overseas dying for no good reason. Answer Answers will vary, but all should give realistic, possible reasons why we should not give military aid to other countries. There should be a logical step from event A (giving military aid) and event B (the answer). Responses might include: it’s too dangerous; the next thing you know, they will be asking for more; we shouldn’t let our military get spread out too thinly, etc. False Dilemma A false dilemma is an argument which presents a lim- ited number of options (usually two), while in reality there are more options. In other words, it gives a choice between one or another (“either-or”) even though there are other choices which could be made. The false dilemma is commonly seen in black or white terms; it sets up one thing as all good and the other as all bad. When one option (typically the “all bad”one) is argued against, the false dilemma concludes that the other must be true. Example Stop wasting my time in this store! Either decide you can afford the stereo, or go without music in your room! This argument contains a logical fallacy because it fails to recognize that there are many other possibil- ities than just buying one particular (expensive) stereo and going without music. You could, for instance, buy a less expensive stereo or even a radio. Or, you could borrow a stereo and have music in your room without making a purchase. There are many options beside the two presented as “either-or” in the argument. Other common false dilemmas include: Love it or leave it. Either you’re with us, or you’re against us. Get better grades or you will never go to college. False dilemmas are also common in politics. Many politicians would like you to believe that they, and their party, have all the right answers, and their opponents are not only wrong, but they are ruining the country. They set up a choice between all good and all bad. Political speeches often include rhetorical ques- tions that contain false dilemmas. For instance: “Price supports on agricultural production are part of the socialist agenda. My opponent in this race consistently votes for price supports on dairy and tobacco products. It is time to stop electing socialists to Congress. Should you vote for my opponent, who wants to lead our coun- try on the path toward socialism, or should you vote for me, and restore democracy? Practice Which of the following is NOT a false dilemma? a. Your grades are lousy. Either study more, or drop out of school. b. We have a big game tonight. Either we will win and be eligible for the tournament, or we will lose and our season will be over. c. Stop driving like a maniac! Either slow down, or take the bus. d. I can’t believe you didn’t vote to raise the mini- mum wage. Either you missed the vote, or you just don’t care about the working poor! – MISUSING DEDUCTIVE REASONING—LOGICAL FALLACIES– 101 Answer Choice b is not a false dilemma. It is a statement of fact that there are only two possible outcomes, a win or a loss. All the other choices present only two options, when in fact there are others to consider. Circular Reasoning A valid deductive argument has a conclusion that fol- lows logically from the premises. It does not infer or assume anything from the premises, but relies only on the information contained within them. In the fallacy of circular reasoning, often called begging the question, you assume as truth the premise you are supposed to be proving. In all valid deductions, the conclusion (what you are trying to prove) follows two premises. In an invalid argument using circular reasoning, the con- clusion follows a single premise. In other words, the premise that is supposed to prove the truth of the con- clusion is simply the conclusion restated with a slight variation. Circular reasoning looks like this: A is B, therefore A is B. When a premise is left out, there is no argument. The person making the claim is simply telling to you believe that what he is telling you is true. Examples 1. “I told you to clean your room!”“Why?” “Because I said so!” 2. “Why do you think the Yankees are the best team in baseball?”“Because they are.” How could these examples go from being invalid to valid, logical arguments? They need to add a second premise that supports, or gives reason for, the conclu- sion. Example 1 might add: “Your room is so messy that you can’t find anything in it,” or, “All of your laundry is on the floor, and it won’t get washed until you clean it up and put it in the washer.” Example 2 could add: “They have won the World Series 26 times in the last 39 appearances,” or,“They are the only team to sweep the World Series ten times.” Practice Which of the following does not beg the question? a. I like the Brewers because they’re my favorite team. b. Ghosts exist because I saw something once that could only have been a ghost. c. The Seafood Shack is the best restaurant in town because it’s so much better than all the others. d. They signed Bruce Springsteen to headline the concert because he’s a rock legend and a huge star. Answer Choice d does not beg the question. It gives two reasons why Springsteen was signed. It would have been an example of circular reasoning if it went: “They signed Bruce Springsteen to headline the concert because he’s a concert headliner.” Equivocation The fallacy of equivocation can be difficult to spot, because both of the premises appear to be true, and sometimes the conclusion seems to follow them. How- ever, in this fallacy, the meaning of a certain word is unclear and it causes the meaning of the entire argu- ment to be invalid. This can occur either by using the same word twice, each time with a different meaning, or by using one word that has an ambiguous meaning. – MISUSING DEDUCTIVE REASONING—LOGICAL FALLACIES– 102 Examples My history professor said everyone who wrote a term paper favoring the sepa- ratists in the Philippines is sick. I guess if I’m sick, I can skip class today. The word “sick” is used in the argument twice, each with a different meaning. The professor meant mentally disturbed, and the student thought he meant physically ill. Hot dogs are better than nothing. Noth- ing is better than steak. Therefore, hot dogs are better than steak. It is not hard to spot the logical fallacy in this argument: the conclusion is obviously wrong although the premises are both true. There is an equivocation in the meaning of the word “nothing;” in the first prem- ise, it means “not a thing,” and in the second premise, it means “no other possible thing.”Using a critical word with two different meanings makes the argument invalid. Now you see how one word with two different meanings can be an equivocation. The other way in which reasoning may be deemed invalid due to this fal- lacy is by using one word that has a number of differ- ent meanings. For example, “My house is by the lake. Why don’t you drop in?” Two meanings of the word “drop” could be right. It might mean, “Why don’t you stop by my house,” or it could mean “why don’t you fall into the lake.” The equivocation of the word “drop” makes the meaning of the sentences unclear.“Save soap and waste paper” is another good example. The word “waste” could mean either the noun “garbage,” or the verb “to use thoughtlessly.” Equivocation can be confusing because it begins with truthful or reasonable premises, which you can agree with. Then, the meaning of a critical word is changed and an illogical or faulty conclusion is drawn. If you follow the argument, you could fall into the trap of agreeing with something you would never have oth- erwise accepted. The best way to handle this fallacy is to get information. Ask for clear definitions of any crit- ical terms that could be used in different ways. When you have pinned them down, they can’t be changed later on. Practice Which word in each example is the equivocation? 1. The sign said “fine for parking here”, and since it was fine, I parked there. 2. The IRS allows a deduction for every dependent in a household. My dog is dependent on me, so I can claim a deduction for him. 3. If all men are created equal, then why are geniuses so smart? 4. Everything that runs has feet. The refrigerator runs, so the refrigerator has feet. Answers 1. fine 2. dependent 3. equal 4. runs – MISUSING DEDUCTIVE REASONING—LOGICAL FALLACIES– 103 . false dilemma. It is a statement of fact that there are only two possible outcomes, a win or a loss. All the other choices present only two options, when in fact there are others to consider. Circular. him. 3. If all men are created equal, then why are geniuses so smart? 4. Everything that runs has feet. The refrigerator runs, so the refrigerator has feet. Answers 1. fine 2. dependent 3. equal 4 lesson explores four of the most common logical fallacies that make deductive reasoning fall apart. 13 99 The argument might have two true premises, and a conclusion that takes them to an extreme.