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common mistakes in thinking
Common Mistakes in Thinking
  • Informal fallacy – An error in reasoning resulting from carelessness, inattention, or insensitivity to language or context in which the argument is presented. In many instances of informal fallacies, we are tempted to accept the argument because we are not attentive enough to recognize that the evidential structure is unacceptable as presented.
  • Informal fallacies are the most common kind of mistake in arguments. They can be hard to avoid or to detect precisely because they are so common. They are the main traps to avoid in arguments and scrupulously avoid in our own.
ad hominem
Ad hominem
  • The first informal fallacy is the argument to the person. The Latin name, argumentum ad hominem, is probably the most commonly used of the Latin words in logic, and sometimes it appears simply as ad hominem. In this fallacy an attack is made on the person presenting the argument rather than on the argument itself. The character, credentials, reputation, position, or office of the individual is called into question instead of the soundness of his o her claim. The person is made to seem ridiculous or suspicious, and this is meant to undermine the argument that is presented.
ad hominem ii
Ad hominem II
  • The ad hominem fallacy actually has two versions, personal and circumstantial. In the personal form (which is the most common one), the character or behavior of the person is discredited. Ad hominem almost always results from saying, in effect,
    • “So – and so’s claim should be rejected because so-and-so is ____________,” where nearly any term with presumably negative impact is placed in the blank (for example, “ignorant,” “a liar,” “a Republican,” “a Democrat, “ “just saying that to get rich,” and so on).
  • Rare exceptions can occur in which a person’s shortcomings do automatically transfer to the person’s claim, but such a transaction takes a peculiar kind of circumstance. For example, “He was paid to lie about this matter.”
ad hominem iii
Ad hominem III
  • In the 19th century the fight for Irish home rule was criticized because its leader, Charles Parnell, was an adulterer. Vincent Van Gogh suffered from severe depression, but that does not have any bearing on the aesthetic value of his paintings.
  • The point is that in judging ideas one mustn’t judge the person presenting the ideas. Insane people can write profound things, the sane can produce a lot of nonsense; awful people can say good things, and saints may not be right in everything they argue.
ad hominem iv
Ad hominem IV
  • In the circumstantial form of ad hominem, the person’s position is cited as the reason to disregard what he or she claims. Example:
    • John says that we should reject what Father Hennesy says about the dangers of abortion because, “After all, he’s a Catholic priest, and priests are required to hold such views.”
  • It may be true that Father Hennesy is a priest and that is views on abortion represent those of the Catholic church. That does not make his views false, however. The specific mistake here, of course, is to presuppose that people always act for their own advantage and because of their position, and that does not seem fair.
ad hominem v
Ad hominem V
  • “Ad hominem” is Latin for “to the man” indicating that it is the person and not the subject matter that’s being addressed.
  • Rather than arguments ad hominem, we must use arguments ad rem, that is, “to the thing itself.”
  • A variety of the fallacy of ad hominem circumstantial is called tu quoque or “you yourself.” Here an argument is discredited because the person does not practice what she preaches. For example, “You tell me not to smoke but you do.” Of course, if someone is seriously against smoking than they should not smoke. However, their judgment is not invalidated by the personal inconsistency.
ad hominem vi
Ad hominem VI
  • This does not mean, of course, that questions about a person’s behavior or position are always beside the point. If we want to know if candidates are fit for office, their character traits are certainly relevant. Such virtues as sincerity, fairness, integrity, and so forth are important considerations. However, we call it “smear tactics” when irrelevant facts about a person’s political position or qualifications for public office. The fact that a woman may be divorced or a lesbian, for example, does not seem relevant to whether she would make a good legislator.
ad hominem vii
Ad hominem VII
  • The argument to the person has its counterpart in the biographical fallacy in literature. Knowing that Virginia Woolf suffered from depression may help us interpret some of her work, but knowing her life has no bearing on the literary value of her novels.
  • In other academic fields the same mistake is termed the genetic fallacy, and it refers to the attempt to explain away a claim by referring to the source.
ad hominem viii
Ad hominem VIII
  • In religion, William James refers to the fallacy as “medical materialism”:
    • “Perhaps the commonest expression of this assumption…is seen in those comments in which unsentimental people so often pass on their more sentimental acquaintances. Alfred believes in immortality so strongly because his temperament is so emotional. Fanny’s extraordinary conscientiousness is merely a matter of overinstigated nerves. William’s melancholy about the universe is due to bad digestion-probably his liver is torpid. Eliza’s delight in her church is a symptom of her hysterical constitution. Peter would be less troubled with his soul if he would take more exercise in the open air, etc.” William James, Varieties of Religious Experience
    • The source of an idea is irrelevant to its truth.
argument from authority
Argument from authority
  • The argument from authority fallacy is committed whenever we argue for some point, not because it is well grounded in fact or logic but because of the authority of the person who presented it. The standing or prestige of a recognized authority is said to guarantee the truth of a claim, and anyone who doubts it is made to feel presumptuous or egotistical. The thrust of the argument is “Who are you to challenge the judgment of this authority or the experience of that expert?”
argument from authority ii
Argument from authority II
  • In some ways this fallacy is the mirror image of the argument to the person. Rather than dismissing a position because of the person who advocates it, in the argument from authority one accepts a position because of the person advocating it. Here too the messenger is confused with the message. Example:
    • Of course different people have different strengths. But Aristotle’s definition of personhood emphasized rationality, so the ability to reason is the only personal characteristic that really matters.
    • Cindy Crawford always drinks Pepsi. If I drink a lot of Pepsi, I might look like Cindy Crawford.
argument from authority iii
Argument from authority III
  • No one can check the evidence for everything that is claimed, so we must depend on the information provided by authorities. However, and idea does not become true simply because an authority says so; the person must have a good reason to say so.
  • If we accept people as authorities it is because we have confidence that they support their insights with good thinking and good evidence. Furthermore, the evidence should be publicly verifiable, whether in the form of reproducible experiments or rational reasons that anyone can consider.
argument from authority iii1
Argument from authority III
  • A wider problem with the argument from authority is it suggests that an authority in one field is also an in another. We make this mistake very often in the fields of sports and entertainment. For instance, outstanding baseball players might be trusted to recommend athletic equipment but they are authority not qualified to endorse camcorders or razors in TV commercials. In the same way, actors are knowledgeable about acting but not necessarily about long distance telephone service, cruise lines, refrigerators, or cars. An ethical problem with such endorsements, of course is that the celebrities may not actually use the product they recommend but are mainly interested in the large endorsement fees.
argument from force
Argument from Force
  • Another informal fallacy is called the argument from force. This fallacy substitutes an appeal to motive in place of evidence in the grounds supporting a claim. In the appeal to force, someone attempts to get you to accept her claim because she somehow will hurt you if you do not agree. Example:
    • Your supervisor at work asks you to support her request for a merit raise. By all accounts, including your personal observation of her performance, she has done a thoroughly miserable job and does not deserve merit recognition in her salary. However, she makes it clear that your job is on the line if you do not support her. So you write the letter supporting her request.
argument from force ii
Argument from Force II
  • Arguments from force amounts to holding a gun to someone’s head and saying, “I trust you will see the force of my argument.” This device can be convincing, and it may ultimately prevail, but not because it has satisfied logical standards. Al Capone once remarked, “You can get more with a kind word and a gun than you can with a kind word.” Of course, it depends on what you are trying to “get”. “You have not converted a man because you have silenced him.” – John Morley

One may get temporary obedience through appeal to force but lose trust, respect, love, honest loyalty, and so forth.

argument from force ii1
Argument from Force II
  • In the argument from force the intimidation sometimes will be overt and physical, as when citizens are compelled to vote for a dictator upon pain of death. However, usually the intimidation is more subtle and indirect. For example, if the boss strongly suggests that an employee agree that the safety standards are adequate, or that an accounting report is accurate, the boss is probably making an argument from force. The employee will feel that he or she had better go along, not blow the whistle, or else the job will go to someone who can “rise above principles.”
argument from force ii2
Argument from Force II
  • In religious discussions people will sometimes say “There are no atheists in foxholes,” implying that we will always turn to religion in times of crisis. Even if that is true, fear is not an argument for God’s existence. The most famous example of the argument from force within religion is “Pascal’s Wager.”
    • Pascal was a seventeenth –century scientist and philosopher. He argued that if we believe in God and we are right, then we will go to heaven; and if we believe in God and we are wrong; then at least we will have a pleasant life on earth thinking that God exists and we will ultimately receive our heavenly reward. On the other hand, if we do not believe in God and we are wrong, then we will surely burn in hell; and if we do not believe in God and we are right, then we will have a miserable life on earth, feeling that no divine mercy, justice or love exists.
argument from force ii3
Argument from Force II
  • Since these are the only options, Pascal argued, we should certainly bet on belief in God because, right or wrong, we are far better off. If we wager on not believing then, right or wrong, we are bound to suffer. In essence, Pascal is arguing that if we know what’s good for us we had better believe in God. Clearly the argument is meant to intimidate us into accepting God’s existence; in this respect it functions as an argument from force. No proof is offered that there is a God, but only that we ought to believe in God to be on the safe side. However, to believe that something is real we need good reasons, not just the fear that we might be sorry if we didn’t.
appeal to pity
Appeal to pity
  • Appeal to pity is a fallacy that is committed whenever the evidential appeal is only to the altruistic ideals of the hearer. Example:
    • Helen is running for a seat on the city council. Though you like her, you have doubts about her qualifications and in fact believe that an opposing candidate would make a better member of the council. When you communicate your concerns about her qualifications to a mutual friend, the friend counters by saying that Helen would be terribly hurt if she were to lose the election. After thinking this over, you conclude that maybe Helen’s qualifications are not so bad after all.
appeal to pity ii
Appeal to pity II
  • The mutual friend has evoked compassion in you for Helen, but she has not given you a reason for changing your opinion of Helen’s qualifications. Does your compassion for Helen enter the picture at all? Certainly, but only in this way: You now have to weigh Helen’s hurt at losing the election against the consequences of having her as a council member instead of the BETTER QUALIFIED candidate. Which, you have to decide, is more important?
appeal to pity ii1
Appeal to pity II
  • As a student you may have used the argument from pity at one time or another. You may have asked for a higher grade on an exam, arguing that you had studied hard but were emotionally upset or swamped with work. You might have said that you have a twenty hour a week job, your car broke down, you were sick with the flu, or that you are having trouble with your parents. Under such circumstances, a sympathetic professor might allow you additional time to do the work or even let you retake the exam, but if the professor were to raise your grade on those grounds he or she would not be acting in a professional way.
appeal to pity iii
Appeal to pity III
  • A higher grade would indicate that you had mastered the material to a greater degree than you actually did, thereby giving a false impression to anyone reading your transcript. Your grade should reflect your actual level of achievement, not how much sympathy the professor felt for you.
  • Imagine being operated on by a doctor who never really mastered the skills of surgery but was given a passing grade by the professor how thought he or she deserved a break. Imagine driving over bridges that were designed by engineers who were allowed to graduate, not because they had met the qualifications, but because they had worked hard and came from poor families.
appeal to pity iv
Appeal to pity IV
  • Let’s look at another example:
    • ROOFER: I’m positive that my work will meet your requirements. I really need the money, what with my wife being sick an all.
  • The roofer seems to be giving a reason for thinking that his work will meet your requirements. But of course he is not; that issue is unaffected by the fact that he really needs the money. This fact is not a reason, not even a bad reason, for concluding anything at all about the quality of his work.
appeal to pity v
Appeal to pity V
  • Notice, though, that actions performed out of concern for others are often rationally and ethically justified. Indeed, in some instances they are among the noblest of human deeds. If the roofer is qualified and needs the money for his wife’s illness, and you are willing to take a chance on him then by all means hire him! Just don’t think that he has given you a reason for thinking that his work will meet your specifications; whether it will or not is something you must establish on other grounds.
straw person
Straw Person
  • Another fallacy is called straw person, the mistake of attributing to your opponents a ridiculous position that they do not hold and that is easily knocked down like a person made of straw. By exaggerating, oversimplifying, or distorting the other person’s views, you set up an easy target. This absurd position, not the person’s actual one, is then refuted by showing how ludicrous it is.
  • The straw person device is frequently used in political rhetoric, functioning as a cheap way of winning points while evading the main issue.
straw person ii
Straw Person II
  • For example, a politician might argue,
    • “My liberal, environmentalist friend believes in preserving species, that the spotted owl and the snail darter are more important than people. I’m sorry, but I cannot share that view. He would not sacrifice a bird or a fish to safeguard a human being, but I would rather let an animal die than a person.”
  • Quite obviously, few if any environmentalists would claim that the life of a bird or fish has a higher value than that of a human being, but the environmentalists position is cast in that light to make it easy to refute. The environmental debate is not over whether we should kill people rather than animals but the extent to which we should endanger wildlife for the sake of economic development.
straw person iii
Straw Person III
  • That, of course, is a genuine question that deserves to be discussed and debated. Should the protection of an endangered species prevent the development of our natural resources, especially if that development means increased employment, energy, and material products to enhance our lives? Are we stewards and caretakers of the earth, or do we have the right, perhaps the obligation, to exploit the earth for human well-being? In cases where the two are incompatible (as often happens in impoverished third world countries) which should take priority? These are real issues , but to frame the debate as a choice between killing animals or people is an unfair caricature.
straw person iv
Straw Person IV
  • Also, can’t environmentalism be compatible with the welfare of human beings? The world can survive without people, but people cannot survive without the world.
poisoning the well
Poisoning the well
  • A sister fallacy to straw person is poisoning the well. Here one side in an argument is placed in a position where it cannot refute the other without discrediting itself. This is done by making the position an undesirable one for any rational or decent person to hold.
    • For example, a moralist might argue, “Women who support abortion are selfish and godless people. They put their own needs above everything and everyone else, and reject the divine gift of a child’s life.” Since most women would not want to be regarded as selfish and godless, they might abandon the argument for abortion on demand.
poisoning the well ii
Poisoning the well II
  • Taking the opposite line, a feminist might argue, “The right of a woman to have an abortion, to do with her body as she pleases , is opposed only by reactionary men who want to keep women in their traditional roles. Every right-thinking person knows this to be true.” At this point any man who believes otherwise is reluctant to oppose abortion for fear of being regarded as a reactionary male and not a right-thinking person. Instances of poisoning the well happen all of the time in daily life. If a couple is quarreling the husband might say, “I find you so defensive and your constant denials that you are defensive only prove my point.” It is impossible then for the women to defend herself, since that would only confirm the defensiveness.
poisoning the well iii
Poisoning the well III
  • We know we are in the presence of the fallacy whenever we come across statements such as “Any caring or concerned person will agree that…,” or “Those who reject my solution are part of the problem,” “Only an idiot would believe…”
  • In arguments, if we come across the ploy of poisoning the well we should expose it for what it is: an attempt to place anyone who disagrees in an impossible position.
slippery slope
Slippery Slope
  • In the slippery slope fallacy we make the mistake of thinking that if we take one step along a certain path then nothing can stop us from sliding inevitably to our ruin. That is, once we set foot on the slippery slope we are bound to end up in disaster. The moral, or course, is that we had better avoid taking that first step.
  • Sometimes the fallacy of the slippery slope is described as the “domino effect”: a slight push on one domino will topple the others and set a whole train of events in motion.
slippery slope ii
Slippery Slope II
  • At other times it is referred to as “opening the floodgates” so that we are inundated and overwhelmed by the forces that we have released. The English often refer to “the thin edge of the wedge,” which suggests that once we allow an opening this will be pushed to some greater, undesirable result. Still other metaphors are “we mustn’t let the genii our of the bottle,” “there is a ripple effect,” “give them an inch and they’ll take a mile,” “events can begin to snowball” (producing an avalanche), and if the camel gets his nose in the tent, he’ll soon have his entire body inside.”
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Slippery Slope III
  • Bureaucrats commit a common example of the slippery slope fallacy when they say, “I would like to help you but if I make an exception for you I will have to make an exception for everyone else. Maybe in your situation there are extenuating circumstances but it is better to stick to the rules, otherwise everybody will claim they are a special case.” The fallacy, of course, is to assume that once you initiate a course of action it is unstoppable. In fact, that is rarely true. That does not mean that rules are made to be broken but that it is possible to break rules without destroying them.
slippery slope iv
Slippery Slope IV
  • Very few rules are without legitimate exceptions, so if bureaucrats insist on absolute rules, they are bound to commit injustices. Of course, any one who claims an exception has the burden of proof to show why the exception should be made.
  • Sometimes slippery slopes do exist. Some developments in science and technology can be dangerous. When we split the atomic nucleus we used the energy for bombs. However, we cannot assume that whenever we take a first step we invariable lose control of events, that actions once unleashed must run their course and produce disaster. Usually we are faced with a flight of stairs, not a long slippery slope, and we can rest on any one of them.
gambler s fallacy
Gambler’s Fallacy
  • The gambler’s fallacy is another important mistake to notice because it can trap people in a cycle of hope and desperation. Gambling has become an enormous business in the United States, exceeding the revenues of movies, books, and recorded music combined. In 1993 alone gambling revenues exceeded $30 billion. As a result of gaming, Las Vegas went from a small desert town of three thousand people to a city of one million, and states are now competing with Indian tribes in the race to build casinos.
gambler s fallacy ii
Gambler’s Fallacy II
  • The gambler’s fallacy is one of the factors that keep people gambling, and it is usually described in terms of “the maturity of the chances.” A person playing roulette, for example, will wait to see which number has not come up in one hundred or two hundred spins of the wheel. Then she will bet on that number on the assumption that, according to statistical probability, the roulette ball is due to fall in that numbered compartment. However, at each turn of the wheel, each number has an equal chance of being chosen.
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Gambler’s Fallacy III
  • You flip a coin ten times, and each time it comes up heads. But on the 11th flip, will it come up heads again, or tails? If you ask a random group of people, you will likely get two different answers.
  • The first will be that the coin will surely come up heads again - it's already done so 10 times in a row, so the odds must be in favor of it happening again. The second answer will be that is must come up tails on the 11th flip, because it came up heads 10 times now and the coin is "due" to go the other way by now.
gambler s fallacy iv
Gambler’s Fallacy IV
  • But both answers are wrong, and both are the different sides of the gambler's fallacy. Even if we come up with 10,000 heads in a row, the odds of number 10,001 being tails is still only 50/50 (assuming that the coin is "fair", of course). The law of averages does not change and a random system does not develop a "memory." The gambler's fallacy represents the very real human desire to find some sort meaning and pattern in what appears to be a random system.
    • As the French mathematician Joseph Bertrand remarked, the coin has neither memory or consciousness.