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Critical Thinking Informal Fallacies In Logic

7. Slippery Slope

The last “content fallacy” that we’re going to look at is “slippery slope”.

Here’s a pretty extreme example of a slippery slope fallacy.

A high school kid’s mom insists that she study on Saturdays. Why? Because if she DOESN’T study on Saturdays then her grades will suffer and she won’t graduate high school with honors, and if she doesn’t graduate with honors then she won’t be able to get into the university of her choice, and ... well, the rest isn’t clear, but the result of all this is that she’ll end up flipping burgers for the rest of her life, and surely she doesn’t want THAT, so she’d better darn well get serious and study!

I’ve actually heard a version of this discussion between two wealthy mothers who were talking about which preschool to send their kids to. The gist was that if they didn’t get their kid into a prestigious preschool then they’d be disadvantaged from that point forward in ways that could ultimately threaten their future life prospects, so this was not a decision to be taken lightly!

I did not envy those kids.

Here’s the schematic form of a slippery slope argument.

1. If A then B
2. If B then C
3. If C then D
4. not-D
Therefore, not-A

It’s a series of connected conditional claims, to the effect that if you assume that A is true or allow A to occur, then B will follow, and if B follows then C will follow, and if C follows then D will follow. But D is something nasty that we all want to avoid, so the conclusion is that if we want to avoid D, we need to reject A, or not allow A to happen.

Note that, as stated, the logic of this argument is fine. In fact, this is a valid argument form that we’ve seen before, we’ve called it “hypothetical syllogism” or “reasoning-in-a-chain” with conditionals.

Slippery slopes are fallacious only if the premises are false or implausible. Everything turns on whether these conditional relationships hold. Sometimes they do, and if they do, it’s not a fallacy. But very often then don’t, and when they don’t we’ve got a slippery slope fallacy.

An Important Caveat

Now, there’s a caveat to this way of analyzing slippery slopes. It’s usually the case that slippery slope arguments aren’t intended to be valid. That is, they’re not intended to establish that the dreaded consequence will follow with absolute certainty. Usually the intent is to argue that if you assume A, then D is very likely to follow, so what’s being aimed for is really a strong argument.

And that means we shouldn’t really be reading the conditional claims as strict conditionals, with every link in the chain following with absolute necessity. We should be asking ourselves, how likely is it that D will follow, if A occurs? If it’s very likely, then the logic is strong, if not then it’s weak. So in a sense we’re evaluating the logic of the argument, but it turns out that in cases like this, the strength of the logic turns on the content of the premises, so in the end we are evaluating the plausibility of premises, which makes this a content fallacy, and not a logical or formal fallacy.

For our example the chain of inferences looks like this:

Doesn’t study on Saturdays →
Doesn’t graduate high school with honors →
Doesn’t get into a top university →
Winds up working in a fast food restaurant (or similar “working class” career”)

This argument is obviously bad, at every stage of the reasoning.

It’s possible that not studying on Saturdays could make a difference to whether the student gets on the honor roll, but there’s no evidence to suggest that this is likely.

Yes, if you’re not on the honor roll then maybe this will affect your chances of getting into a top university, but without specifying what counts as a top university, and what other factors may or may not be operating (like, for example, whether the student is a minority or an athlete and might be eligible for non-academic scholarships of various kinds), then it’s impossible to assess the chances of this case.

The last move, from failing to get into a top university to flipping burgers for a living, is obviously the weakest link in the chain, this is just wildly pessimistic speculation with nothing to support it.

So each link in the chain is weak, and the chain as a whole simply compounds these weaknesses.

By saying this we’re saying that premises 1, 2 and 3 are not plausible, and so the inference from A to D is not plausible. We have no reason to think that this slope is “slippery”.

* * *

Now, there’s another obvious way that one can attack a slippery slope argument. You might be willing to grant that the slope is slippery, but deny that what awaits at the bottom of the slope is really all that bad.

This would be to challenge premise 4, “not-D”. “not-D” says that D is objectionable in some way, that we don’t want to accept D. But this might be open to debate. If what awaits at the bottom of the slope is “and then you die a painful death”, or “and then all our civil rights are taken away”, then sure, just about everyone is going to agree that that’s a bad outcome.

But it’s not as obvious that everyone will find flipping burgers objectionable, or whatever this notion stands for — working in the service industry, or working in a low-paying job, or whatever.

What’s important in evaluating a slippery slope argument is that the intended audience of the argument finds the bottom of the slope objectionable. So this is another way to criticize a slippery slope argument — by arguing that the outcome of this chain of events really isn’t as objectionable as the arguer would like you to think.


So, just to summarize what we’ve said so far, there are two ways of challenging a slippery slope argument.

  1. Challenge the strength of the conditional relationships that the argument relies on. When people say that a slippery slope argument is fallacious, they usually mean that this chain of inferences is weak.
  2. Challenge the “objectionableness” of whatever lies at the end of the chain. If it’s not obvious to the intended audience that this is actually a bad thing, then the argument will fail to persuade, regardless of how slippery the slope may be.

Some Comments on Assessing the Plausibility of Conditional Claims

Before wrapping up, I’d like to make a few points about assessing the plausibility of conditional chains. Fallacious slippery slope arguments often succeed at persuading their audience because people misjudge the strength of the chain of inferences. They’re prone to thinking that the chain is stronger than it actually is.

It’s important to realize two things. First, a chain of conditional inferences is only as strong as its weakest link. The weakest conditional claim, the one that is least likely to be true, is the one that sets the upper bound on the strength of the chain as a whole. So even if some of the inferences in the chain are plausible, the chain itself is only as strong as the weakest inference.

Second, weaknesses in the links have a compounding effect, so the strength of the whole chain is almost always much weaker than the weakest link. To see why this is so, you can think of conditional claims as probabilistic inferences — If A is true, then B follows with some probability, and this probability is usually less than 1, or less than 100%.

So the probability of D following from A, the probability of the whole inference, is actually a multiplicative product of the probabilities of each of the individual links.

The odds of a coin landing heads on a single toss is 1/2, or 50%. The odds of a coin landing heads twice in a row is 1/2 times 1/2, or 1/4, which is 25%. Conditional inferences compound in a similar way.

So, if the odds for each link in the chain were, let’s say, 90%, then the odds of the whole chain being true, of D actually following from A, would only be 0.73, or 73%, and this number will go down further with each additional link in the chain.

People, in general, are very bad at estimating compound probabilities, and we’ll tend to overestimate them.

What’s the estimate if the one of the links is weaker than the rest, say, 0.6, or 60%. The probability of D following from A actually drops below 50%, a very weak inference, but very few people will read the probabilities this way. Their attention will focus on the highly probable bits of the story and their estimate of the overall odds will be anchored to these bits, especially if they’re either at the very beginning or at the very end of the chain, since these make the biggest impression.

So, human beings in general are quite vulnerable to slippery slope reasoning, and knowing these facts should motivate you to be more critical when you encounter these kinds of arguments.

by David Ferrer

A logical fallacy is an error in reasoning common enough to warrant a fancy name. Knowing how to spot and identify fallacies is a priceless skill. It can save you time, money, and personal dignity. Formal fallacies are breakdowns in how you say something, the ideas are ordered wrong somehow. Their form is wrong.

Informal fallacies, like the ones below, have to do with what you are saying (the “content” of an argument). The ideas might be arranged right, but something you said isn’t quite right. The content is wrong. Here’s a list of the 15 informal fallacies you are most likely to encounter in discussion and debate.

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1. Ad Hominem Fallacy

When people think of “arguments,” often their first thought is of shouting matches riddled with personal attacks. Ironically, personal attacks run contrary to rational arguments. In logic and rhetoric, personal attacks are called ad hominems. Ad hominem is Latin for “against the man.” Instead of advancing good sound reasoning, ad hominems replace logical argumentation with attack-language unrelated to the truth of the matter.

More specifically, ad hominems are a fallacy of relevance where someone rejects or criticizes another person’s view on the basis of personal characteristics, background, physical appearance, or other features irrelevant to the argument at issue.

An ad hominem is more than just an insult. It’s an insult used as if it were an argument or evidence in support of a conclusion. Verbally attacking people proves nothing about the truth or falsity of their claims. Ad hominems are common known in politics as “mudslinging.” Instead of addressing the candidate’s stance on the issues, or addressing his or her effectiveness as a statesman or stateswoman, ad hominems focus on personality issues, speech patterns, wardrobe, style, and other things that affect popularity but have no bearing on their competence. In this way, ad hominemscan be unethical, seeking to manipulate voters by appealing to irrelevant foibles and name-calling instead of addressing core issues. In this last election cycle, personal attacks were volleyed freely from all sides of the political aisle, with both Clinton and Trump facing their fair share of ad hominems.

Ad hominem is an insult used as if it were an argument or evidence in support of a conclusion.

A thread on Quora lists the following doozies against Hillary Clinton: “Killary Clinton,” “Crooked Hillary,” “Hilla the Hun,” “Shillary,” “Hitlery,” “Klinton,” “Hildebeest,” “Defender of Child rapists,” “Corporate Whore,” “Mr. President,” “Heil Hillary,” “Wicked Witch of the West Wing,” “Robberty Hillham Clinton,” “Mrs. Carpetbagger”, and the decidedly unsubtle, “The Devil.”

The NY Daily News offers an amusing list of insults against Donald Trump: “Short fingered Vulgarian,” “Angry Creamsicle,” “Fascist Carnival Barker,” “F*ckface von Clownstick,” “Decomposing Jack-O-Lantern,” “Chairman of the Saddam Hussein Fanclub,” “Racist Clementine,” “Sentient Caps Lock Button,” “Cheeto Jesus,” “Tangerine Tornado,” and perhaps the most creative/literary reference, “Rome Burning in Man Form.”

Ad hominems often signal the point at which a civil disagreement has descended into a “fight.” Whether it’s siblings, friends, or lovers, most everyone has had a verbal disagreement crumble into a disjointed shouting match of angry insults and accusations aimed at discrediting the other person. When these insults crowd out a substantial argument, they become ad hominems.

See if you can tell which of these is an ad hominem and which is just an insult.

Example 1: “MacDougal roots for a British football team. Clearly he’s unfit to be a police chief in Ireland.”
Example 2: “All people from Crete are liars”

2. Straw Man

It’s much easier to defeat your opponent’s argument when it’s made of straw. The Strawman fallacy is aptly named after a harmless, lifeless, scarecrow. In the straw man fallacy, someone attacks a position the opponent doesn’t really hold. Instead of contending with the actual argument, he or she instead attacks the equivalent of a lifeless bundle of straw, an easily defeated effigy, which the opponent never intended upon defending anyway.

Straw man fallacies are a cheap and easy way to make one’s position look stronger than it is. Using this fallacy, opposing views are characterized as “non-starters,” lifeless, truthless, and wholly unreliable. By comparison, one’s own position will look better for it. You can imagine how straw man fallacies and ad hominems can occur together, demonizing opponents and discrediting their views.

In the straw man fallacy, someone attacks a position the opponent doesn’t really hold.

This fallacy can be unethical if it’s done on purpose, deliberately mischaracterizing the opponent’s position for the sake of deceiving others. But often the straw man fallacy is accidental, because one doesn’t realize he or she is oversimplifying a nuanced position, or misrepresenting a narrow, cautious claim as if it were broad and foolhardy.

See if you can detect how both of the following statements could qualify as a strawman fallacy.

Example 1: “The Senator thinks we can solve all our ecological problems by driving a Prius.”
Example 2: “Quite the contrary, the Senator thinks the environment is such a wreck that no one’s car choice or driving habits would make the slightest difference.”

3. Appeal to Ignorance (argumentum ad ignorantiam)

Any time ignorance is used as a major premise in support of an argument, it’s liable to be a fallacious appeal to ignorance. Naturally, we are all ignorant of many things, but it is cheap and manipulative to allow this unfortunate aspect of the human condition to do most of our heavy lifting in an argument.

Ignorance isn’t proof of anything except that one doesn’t know something.

Interestingly, this fallacy is often used to bolster multiple contradictory conclusions at once. Consider the following two claims: “No one has ever been able to prove definitively that extra-terrestrials exist, so they must not be real.” “No one has ever been able to prove definitively that extra-terrestrials do not exist, so they must be real.” If the same argument strategy can support mutually exclusive claims, then it’s not a good argument strategy.

Ignorance isn’t proof of anything except that one doesn’t know something. If no one has proven the non-existence of ghosts or flying saucers, that’s hardly proof that those things exist or don’t exist. If we don’t know whether they exist, then we don’t know that they exist or that they don’t exist. Ignorance doesn’t prove any claim to knowledge.

Consider the following examples:

Example 1: “We have no evidence that the Illuminati ever existed. They must have been so clever they destroyed all the evidence.”
Example 2: “I know nothing about Tank Johnson except that he has a criminal record as long as your leg, but I’ll bet he’s really just misunderstood.”

4. False Dilemma/False Dichotomy

This fallacy has a few other names: “black-and-white fallacy,” “either-or fallacy,” “false dichotomy,” and “bifurcation fallacy.” This line of reasoning fails by limiting the options to two when there are in fact more options to choose from. Sometimes the choices are between one thing, the other thing, or both things together (they don’t exclude each other). Sometimes there are a whole range of options, three, four, five, or a hundred and forty-five. However it may happen, the false dichotomy fallacy errs by oversimplifying the range of options.

Dilemma-based arguments are only fallacious when, in fact, there are more than the stated options. It’s not a fallacy however if there really are only two options. For example, “either Led Zeppelin is the greatest band of all time, or they are not.” That’s a true dilemma, since there really are only two options there: A or non-A. It would be fallacious however to say, “there are only two kinds of people in the world, people who love Led Zeppelin, and people who hate music.” Some people are indifferent about that music. Some sort of like it, or sort of dislike it, but don’t have strong feelings either way.

Dilemma-based arguments are only fallacious when, in fact, there are more than the stated options.

The false dilemma fallacy is often a manipulative tool designed to polarize the audience, heroicizing one side and demonizing the other. It’s common in political discourse as a way of strong-arming the public into supporting controversial legislation or policies.

See if you can identify a third option these politicians failed to mention.

Example 1: “Either we go to war or we appear weak.”
Example 2: “Either you love me, or you hate me.”

5. Slippery Slope

You may have used this fallacy on your parents as a teenager: “But, you have to let me go to the party! If I don’t go to the party, I’ll be a loser with no friends. Next thing you know I’ll end up alone and jobless living in your basement when I’m 30!” The slippery slope fallacy works by moving from a seemingly benign premise or starting point and working through a number of small steps to an improbable extreme.

This fallacy is not just a long series of causes. Some causal chains are perfectly reasonable. There could be a complicated series of causes which are all related, and we have good reason for expecting the first cause to generate the last outcome. The slippery slope fallacy, however, suggests that unlikely or ridiculous outcomes are likely when there’s just not enough evidence to think so.

The slippery slope fallacy, however, suggests that unlikely or ridiculous outcomes are likely when there’s just not enough evidence to think so.

Certain ad campaigns from Dodge, Taco Bell, and notably a recent one for Direct TV, commit this fallacy to great comic effect.

It’s hard enough to prove one thing is happening or has happened; it’s even harder to prove a whole series of events will happen. That’s a claim about the future, and we haven’t arrived there yet. We, generally, don’t know the future with that kind of certainty. The slippery slope fallacy slides right over that difficulty by assuming that chain of future events without really proving their likelihood.

Which of these examples is a slippery slope fallacy and which is not?

Example 1: “Your coach’s policy is that no one can be a starter on game day if they miss practice. So, if you miss basketball practice today, you won’t be a starter in Friday’s game. Then you won’t be the first freshman to start on the Varsity basketball team at our school.”
Example 2: “If America doesn’t send weapons to the Syrian rebels, they won’t be able to defend themselves against their warring dictator. They’ll lose their civil war, and that dictator will oppress them, and the Soviets will consequently carve out a sphere of influence that spreads across the entire Middle East.”

6. Circular Argument (petitio principii)

When a person’s argument is just repeating what they already assumed beforehand, it’s not arriving at any new conclusion. We call this a circular argument or circular reasoning. If someone says, “the Bible is true because the Bible says it’s true”—that’s a circular argument. One is assuming that the Bible only speaks truth, and so they trust it to truthfully report that it speaks the truth. Another example of circular reasoning is, “According to my brain, my brain is reliable.” Well, yes, of course we would think our brains are in fact reliable if our brains are the one’s telling us that our brains are reliable.

Circular arguments are also called Petitio principii meaning “Assuming the initial [thing]” (commonly mistranslated as “begging the question”). This fallacy is a kind of presumptuous argument where it only appears to be an argument. It’s really just restating one’s assumptions in a way that looks like an argument. You can recognize a circular argument when the conclusion also appears as one of the premises in the argument.

Another way to explain circular arguments is that they start where they finish, and finish where they started. See if you can identify which of these is a circular argument.

Example 1: “Abstract art isn’t even art. Those pictures and sculptures don’t represent anything, and that’s how you know its not even art.”
Exmaple 2: “We should be tolerant even of people who believe intolerant ideas. Their ideas matter too, and we can still learn different things from them even if their particular intolerant idea is wrong.”

7. Hasty Generalization

Hasty generalizations are general statements without sufficient evidence to support them. They are general claims too hastily made, hence they commit some sort of illicit assumption, stereotyping, unwarranted conclusion, overstatement, or exaggeration.

Normally we generalize without any problem. We make general statements all the time: “I like going to the park,” “Democrats disagree with Republicans,” “It’s faster to drive to work than to walk,” or “Everyone mourned the loss of Harambe, the Gorilla.”

Hasty generalization may be the most common logical fallacy because there’s no single agreed-upon measure for “sufficient” evidence.

Indeed, the above phrase “all the time” is a generalization—we aren’t all the time making these statements. We take breaks to do other things like eat, sleep, and inhale. These general statements aren’t addressing every case every time. They are speaking generally, and, generally speaking, they are true. Sometimes you don’t enjoy going to the park. Sometimes Democrats and Republicans agree. Sometimes driving to work can be slower than walking if the roads are all shut down for a Harambe procession.

Hasty generalization may be the most common logical fallacy because there’s no single agreed-upon measure for “sufficient” evidence. Is one example enough to prove the claim that “Apple computers are the most expensive computer brand?” What about 12 examples? What about if 37 out of 50 apple computers were more expensive than comparable models from other brands?

There’s no set rule for what constitutes “enough” evidence. In this case, it might be possible to find reasonable comparison and prove that claim is true or false. But in other cases, there’s no clear way to support the claim without resorting to guesswork. The means of measuring evidence can change according to the kind of claim you are making, whether it’s in philosophy, or in the sciences, or in a political debate, or in discussing house rules for using the kitchen. A much safer claim is that “Apple computers are more expensive than many other computer brands.”

Meanwhile, we do well to avoid treating general statements like they are anything more than generalizations. Even if it were generally true that women are bad drivers—and I’m not saying they are—there are still plenty of women who are good drivers. And those “cases” just aren’t covered with that general statement even if it were true. In my case, my wife is a better driver than I am. So I do well not to generalize too widely.

A simple way to avoid hasty generalizations is to add qualifiers like “sometimes,” “maybe,” “often,” or “it seems to be the case that . . . “. When we don’t guard against hasty generalization, we risk stereotyping, sexism, racism, or simple incorrectness. But with the right qualifiers, we can often make a hasty generalization into a responsible and credible claim.

Which of the following is a hasty generalization

Example 1: “Some people vote without seriously weighing the merits of the candidate.”
Example 2: “People nowadays only vote with their emotions instead of their brains.”

8. Red Herring (ignoratio elenchi)

A “red herring” is a distraction from the argument typically with some sentiment that seems to be relevant but isn’t really on-topic. Typically, the distraction sounds relevant but isn’t quite on-topic. This tactic is common when someone doesn’t like the current topic and wants to detour into something else instead, something easier or safer to address. Red herrings are typically related to the issue in question but aren’t quite relevant enough to be helpful. Instead of clarifying and focusing they confuse and distract.

Red herrings can be difficult to identify because it’s not always clear how different topics relate.

The phrase “red herring” refers to a kippered herring (salted herring-fish) which was reddish brown in color and quite pungent. According to legend, this aroma was so strong and delectable to dogs that it served as a good training device for testing how well a hunting dog could track a scent without getting distracted. Dogs aren’t generally used for hunting fish so a red herring is a distraction from what he is supposed to be hunting.

Red herrings can be difficult to identify because it’s not always clear how different topics relate. A “side” topic may be used in a relevant way, or in an irrelevant way. In the big meaty disagreements of our day, there are usually a lot of layers involved, with different subtopics weaving into them. We can guard against the red herring fallacy by clarifying how our part of the conversation is relevant to the core topic.

Which of the following examples is a red herring fallacy?

Example 1: “My wife wants to talk about cleaning out the garage, so I asked her what she wants to do with our patio furniture? Now she’s shopping for new patio furniture and not bothering me about the garage.”
Example 2: “My wife wants to talk about cleaning out the garage, so I asked her what she wants to do with the patio furniture? It’s just sitting in the garage taking up space.”

9. Tu Quoque Fallacy

The “tu quoque,” Latin for “you too,” is also called the “appeal to hypocrisy” because it distracts from the argument by pointing out hypocrisy in the opponent. This tactic doesn’t solve the problem, or prove one’s point, because even hypocrites can tell the truth. Focusing on the other person’s hypocrisy is a diversionary tactic. In this way, the tu quoque typically deflects criticism away from one’s self by accusing the other person of the same problem or something comparable.  If Jack says, “Maybe I committed a little adultery, but so did you Jason!” Jack is trying to diminish his responsibility or defend his actions by distributing blame to other people. But no one else’s guilt excuses his own guilt. No matter who else is guilty, Jack is still an adulterer.

The tu quoque fallacy is an attempt to divert blame, but it really only distracts from the initial problem. To be clear, however, it isn’t a fallacy to simply point out hypocrisy where it occurs. For example, Jack may say, “yes, I committed adultery. Jill committed adultery. Lots of us did, but I’m still responsible for my mistakes.” In this example, Jack isn’t defending himself or excusing his behavior. He’s admitting his part within a larger problem. The hypocrisy claim becomes a fallacy only when the arguer uses some (apparent) hypocrisy to neutralize criticism and distract from the issue.

Which of the following is a tu quoque fallacy

Example 1: “But, Dad, I know you smoked when you were my age, so how can you tell me not to do it?”
Example 2: “Son, yes, I smoked when I was your age, it was dumb then. And it’s dumb now. That’s why I forbid you to smoke, chew, or vape, or use nicotine gum, or whatever you kids do with tobacco these days.”

10. Causal Fallacy

The Causal Fallacy is any logical breakdown when identifying a cause. You can think of the Causal Fallacy as a parent category for several different fallacies about unproven causes.

One causal fallacy is the False Cause or non causa pro causa (“not the-cause for a cause”) fallacy, which is when you conclude about a cause without enough evidence to do so. Consider, for example, “Since your parents named you ‘Harvest,’ they must be farmers.” It’s possible that the parents are farmers, but that name alone is not enough evidence to draw that conclusion. That name doesn’t tell us much of anything about the parents. This claim commits the False Cause Fallacy.

Another causal fallacy is the Post Hoc fallacy. Post hoc is short for post hoc ergo propter hoc (“after this, therefor because of this”). This fallacy happens when you mistake something for the cause just because it came first. The key words here are “Post” and “propter” meaning “before” and “cause.” Just because this came before that doesn’t mean this caused that. Post doesn’t prove propter. A lot of superstitions are susceptible to this fallacy. For example:

“Yesterday, I walked under a ladder with an open umbrella indoors while spilling salt in front of a black cat. And I forgot to knock on wood with my lucky dice. That must be why I’m having such a bad day today. It’s bad luck.”

Now, it’s theoretically possible that those things cause bad luck. But since those superstitions have no known or demonstrated causal power, and “luck” isn’t exactly the most scientifically reliable category, it’s more reasonable to assume that those events, by themselves, didn’t cause bad luck. Perhaps that person’s “bad luck” is just his own interpretation because he was expecting to have bad luck. He might be having a genuinely bad day, but we cannot assume some non-natural relation between those events caused today to go bad. That’s a Post Hoc fallacy. Now, if you fell off a ladder onto an angry black cat and got tangled in an umbrella, that will guarantee you one bad day.

Another kind of causal fallacy is the correlational fallacy also known as cum hoc ergo property hoc (Lat., “with this therefore because of this”). This fallacy happens when you mistakenly interpret two things found together as being causally related. Two things may correlate without a causal relation, or they may have some third factor causing both of them to occur. Or perhaps both things just, coincidentally, happened together. Correlation doesn’t prove causation.

Consider for example, “Every time Joe goes swimming he is wearing his Speedos. Something about wearing that Speedo must make him want to go swimming.” That statement is a correlational fallacy. Sure it’s theoretically possible that he spontaneously sports his euro-style swim trunks, with no thought of where that may lead, and surprisingly he’s now motivated to dive and swim in cold, wet nature. That’s possible. But it makes more sense that he put on his trunks because he already planned to go swimming.

Which kind of causal fallacy is at work in these examples?

Example 1: “Jimmy isn’t at school today. He must be on a family trip.”
Example 2: “Jimmy has a fever, sinus congestion, a cough, and can’t come to school, so he probably has a test later today.”
Example 3: “Someone really should move this ‘Deer Crossing’ sign. This is a dangerous stretch of highway and the deer really should be crossing somewhere else.”

11. Fallacy of Sunk Costs

Sometimes we invest ourselves so thoroughly in a project that we’re reluctant to ever abandon it, even when it turns out to be fruitless and futile. It’s natural, and usually not a fallacy to want to carry on with something we find important, not least because of all the resources we’ve put into it. However, this kind of thinking becomes a fallacy when we start to think that we should continue with a task or project because of all that we’ve put into it, without considering the future costs we’re likely to incur by doing so. There may be a sense of accomplishment when finishing, and the project might have other values, but it’s not enough to justify the cost invested in it.

We are susceptible to this errant behavior when we crave that sense of completion or a sense of accomplishment

“Sunk cost” is an economic term for any past expenses that can no longer be recovered. For example, after watching the first 6 episodes of Battlestar Galactica, you decide the show isn’t for you. Those six episodes are your “sunk cost.” But, because you’ve already invested roughly 6 hours of your life into it, you rationalize that you might as well finish it. All apologies to Edward James Olmos, but this isn’t “good economics” so to speak. It’s more cost than benefit.

Psychologically, we are susceptible to this errant behavior when we crave that sense of completion or a sense of accomplishment, or we are too comfortable or too familiar with this unwieldy project. Sometimes, we become too emotionally committed to an ‘investment,’ burning money, wasting time, and mismanaging resources to do it.

Consider the following examples. Which of these is a sunk cost fallacy and which is not?

Example 1: “I know this relationship isn’t working anymore and that we’re both miserable. No marriage. No kids. No steady job. But I’ve been with him for 7 years, so I better stay with him.”
Example 2: “I’m halfway done with college. This is so tough, and It’s not nearly as fun as I thought it would be, but I don’t know. I guess I’ll finish it and get my degree.”

12. Appeal to Authority (argumentum ad verecundiam)

This fallacy happens when we misuse an authority. This misuse of authority can occur in a number of ways. We can cite only authorities—steering conveniently away from other testable and concrete evidence as if expert opinion is always correct. Or we can cite irrelevant authorities, poor authorities, or false authorities.

Like many of the other fallacies in this list, the argumentum ad verecundiam (“argument from respect”) can be hard to spot. It’s tough to see, sometimes, because its normally a good responsible move to cite relevant authorities supporting your claim. It can’t hurt. But if all you have are authorities, and everyone just has to “take their word for it” without any other evidence to show that those authorities are correct, well then you have a problem.

Often this fallacy refers to irrelevant authorities—like citing a foot doctor when trying to prove something about Psychiatry; his or her expertise is in an irrelevant field. When citing authorities to make your case, you need to cite relevant authorities, but you also need to represent them correctly, and make sure their authority is legitimate.

Suppose someone says, “I buy Fruit of the Loom™ underwear because Michael Jordan says it’s the best.” But Michael Jordan isn’t a relevant authority when it comes to underwear. This is a fallacy of irrelevant authority.

Now consider this logical leap: “4 out of 5 dentists agree that brushing your teeth makes your life meaningful.” Dentists generally have expert knowledge about dental hygiene, but they aren’t qualified to draw far-reaching conclusions about its meaningfulness. This is a fallacy of misused authority. For all we know, their beliefs about the “meaning of life” are just opinions, not expert advice.

Or take the assumption that “I’m the most handsome man in the world because my Mommy says so.” Now, while I might be stunningly handsome, my Mom’s opinion doesn’t prove it. She’s biased. She’s practically required to tell me I’m handsome because it’s her job as a mother to see the best in me and to encourage me to be the best I can be. She’s also liable to see me through “rose-colored glasses.” And, in this case, she’s not an expert in fashion, modeling, or anything dealing in refined judgments of human beauty. She’s in no position to judge whether I’m the most handsome man in the world. Her authority there is illusory. (Sorry Mom.)

There’s another problem with relying too heavily on authorities. Even the authorities can be wrong sometimes. The science experts in the 16th century thought the earth was the center of the solar system (Geocentrism). Turns out they were wrong. The leading scientists, in the 19th century, thought the universe as we know it always existed (Steady State theory). They too were wrong. For these reasons, it’s a good general rule to treat authorities as helpful guides with suggestive evidence. But even authorities deserve a fair share of skepticism since they can make mistakes, overstep their expertise, and otherwise mislead you.

Consider the following examples. How do these statements mishandle authorities?

Example 1: “Because Martin Sheen played the president on Television, he’d probably make a great president in real life.”
Example 2: “One day robots will enslave us all. It’s true. My computer science teacher says so.”
Example 3: “This internet news site said that the candidate punches babies. We know that’s true because it’s on the internet.”

13. Equivocation (ambiguity)

Equivocation happens when a word, phrase, or sentence is used deliberately to confuse, deceive, or mislead by sounding like it’s saying one thing but actually saying something else. Equivocation comes from the roots “equal” and “voice” and refers to two-voices; a single word can “say” two different things. Another word for this is ambiguity.

When it’s poetic or comical, we call it a “play on words.” But when it’s done in a political speech, an ethics debate, or in an economics report, for example, and it’s done to make the audience think you’re saying something you’re not, that’s when it becomes a fallacy. Sometimes, this is not a “fallacy” per se, but just a miscommunication. The equivocation fallacy, however, has a tone of deception instead of just a simple misunderstanding. Often this deception shows up in the form of euphemisms, replacing unpleasant words with “nicer” terminology. For example, a euphemism might be replacing “lying” with the phrase “creative license,” or replacing my “criminal background” with my “youthful indiscretions,” or replacing “fired from my job” with “early retirement.” A romantically involved couple might discuss their relationship to others as “just friends” so they appear like they have no other romantic relations. When these replacement words are used to mislead people they become an equivocation fallacy.

Which of these examples is an equivocation fallacy?

Example 1: “His political party wants to spend your precious tax dollars on big government. But my political party is planning strategic federal investment in critical programs.”
Example 2: “I don’t understand why you’re saying I broke a promise. I said I’d never speak again to my ex-girlfriend. And I didn’t. I just sent her some pictures and text messages.”

14. Appeal to Pity (argumentum ad misericordiam)

Argumentum ad misericordiam is Latin for “argument to compassion”. Like the ad hominem fallacy above, it is a fallacy of relevance. Personal attacks, and emotional appeals, aren’t strictly relevant to whether something is true or false. In this case, the fallacy appeals to the compassion and emotional sensitivity of others when these factors are not strictly relevant to the argument. Appeals to pity often appear as emotional manipulation. For example,

“How can you eat that innocent little carrot? He was plucked from his home in the ground at a young age, and violently skinned, chemically treated, and packaged, and shipped to your local grocer and now you are going to eat him into oblivion when he did nothing to you. You really should reconsider what you put into your body.”

Obviously, this characterization of carrot-eating is plying the emotions by personifying a baby carrot like it’s a conscious animal. So, by the time the conclusion appears, it’s not well-supported. If you are to be logically persuaded to agree that “you should reconsider what you put into your body,” then it would have been better evidence to hear about unethical farming practices or unfair trading practices such as slave labor, toxic runoffs from fields, and so on.

Truth and falsity aren’t emotional categories, they are factual categories. They deal in what is and is not, regardless of how one feels about the matter. Another way to say it is that this fallacy happens when we mistake feelings for facts. Our feelings aren’t disciplined truth-detectors unless we’ve trained them that way. So, as a general rule, it’s problematic to treat emotions as if they were (by themselves) infallible proof that something is true or false. Children may be scared of the dark for fear there are monsters under their bed, but that’s hardly proof of monsters.

Truth and falsity aren’t emotional categories, they are factual categories.

To be fair, emotions can sometimes be relevant. Often, the emotional aspect is a key insight into whether something is morally repugnant or praiseworthy, or whether a governmental policy will be winsome or repulsive. People’s feelings about something can be critically important data when planning a campaign, advertising a product, or rallying a group together for a charitable cause. But it becomes a fallacious appeal to pity when the emotions are used in substitution for facts or as a distraction from the facts of the matter.

It’s not a fallacy for jewelry and car companies to appeal to your emotions to persuade you into purchasing their product. That’s an action, not a claim, so it’s can’t be true or false. It would however be a fallacy if they used emotional appeals to prove that you need this car, or that this diamond bracelet will reclaim your youth, beauty, and social status from the cold clammy clutches of Father Time. The fact of the matter is, you probably don’t need those things, and they won’t rescue your fleeting youth.

Which of these is a fallacious appeal to emotion, and which one is not?

Example 1: “The government needs to hear our cry because we are scared. We are scared that this candidate will not respect us or protect us. We are scared about our future. There’s no hope for people like us with these candidates in office.”
Example 2: “These candidates stated that they would close down the education department and that has many teachers worried about their jobs in 2017.”

15. Bandwagon Fallacy

The bandwagon fallacy assumes something is true (or right, or good) because other people agree with it. A couple different fallacies can be included under this label, since they are often indistinguishable in practice. The ad populum fallacy (Lat., “to the populous/popularity”) is when something is accepted because it’s popular. The concensus gentium (Lat., “consensus of the people”) is when something is accepted because the relevant authorities or people all agree on it. And the status appeal fallacy is when something is considered true, right, or good because it has the reputation of lending status, making you look “popular,” “important,” or “successful.”

For our purposes, we’ll treat all of these fallacies together as the Bandwagon Fallacy. According to legend, politicians would parade through the streets of their district trying to draw a crowd and gain attention so people would vote for them. And whoever supported that candidate was invited to literally jump on board the bandwagon. Hence the nickname “Bandwagon Fallacy.”

This tactic is common among advertisers. “If you want to be like Mike (Jordan), you’d better eat your Wheaties.” “Drink Gatorade because that’s what all the professional athletes do to stay hydrated.” “McDonald’s has served over 99 billion, so you should let them serve you too.” The form of this argument often looks like this: “Many people do or think X, so you ought to do or think X too.”

One problem with this kind of reasoning is that the broad acceptance of some claim or action is not always a good indication that the acceptance is justified. People can be mistaken, confused, deceived, or even willfully irrational. And when people act together, sometimes they become even more foolish—i.e., “mob mentality.” People can be quite gullible, and this fact doesn’t suddenly change when applied to large groups. Which of these is a bandwagon fallacy?

Example 1: “Almost everyone at my school will be at the party Friday night. It must be a popular thing to do.”
Example 2: “Almost everyone at my school will be at the party Friday night. It must be the right thing to do.”

We hope this little primer on logical fallacies helps you to navigate future disputes with friends, family and unhinged online acquaintances without descending into vitriol or childish name-calling. Or at least if it does descend into vitriol and childish name-calling, you’ll be in a great position to rhetorically trounce your opponent with sound reasoning and airtight logic.

Did we miss any commonplace logical fallacies? Let us know in the comments section below!

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