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Flashcards in Named Logical Flaws Deck (18)
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1

IDENTIFY THE FLAW:

 

Amy argues that we should not tear down statues of historical figures, because we shouldn't judge them according to the moral standards of current society. However, Amy is known to have cheated her way through college and defends policies that hurt non-wealthy communities. So we should not listen to her and instead should tear down the statues.

ATTACKING THE SOURCE (AD HOMINEM)

This argument is flawed because it doesn't try to engage with the merits of Amy's argument. Instead, it attacks her as a person. But Amy's background and the kinds of policies she supports are logically irrelevant to her argument; they have no bearing on whether we should tear down the statues. 

 

2

IDENTIFY THE FLAW:

 

People who eat red meat over 3 times per week develop heart disease at a higher rate than people who eat red meat less often. Thus, eating red meat will increase the chances that you will develop heart disease.

CORRELATION TO CAUSE

The premise establishes a correlation between eating red meat over 3 times per week and heart disease. But that doesn't mean red meat is what's causes the increased rate of heart disease in the meat-eaters. Maybe there's a third factor involved - what if the people who eat red meat over 3 times per week also eat more cheese or smoke more or exercise less than the people who eat red meat less often? 

3

IDENTIFY THE FLAW:

Anyone who plagiarizes will be suspended. Ronald was recently suspended. Thus, we know that he must have plagiarized.

 

CONFUSING SUFFICIENT AND NECESSARY

The premise tells us that plagiarizing is sufficient for suspension. But that doesn't mean it's the only way someone would be suspended. It's not necessary for suspension. There could be other reasons Ronald was suspended (murder, drug trafficking, etc.). This argument confuses a sufficient condition (plagiarizing) for a necessary condition.

4

IDENTIFY THE FLAW:

My friend is considering a gym membership and a membership at a spinning class. Since she prefers to have options for how to work out, and the gym membership offers her more workout options than the spinning class, she will probably choose the gym membership instead of the spinning class.

EXCLUSIVITY (FAILS TO EXCLUDE POSSIBILITY OF BOTH)

The premises never established that my friend can't choose to do both the gym membership and the spinning class. Sure, she prefers to have options for how to work out, but doesn't that suggest she could opt to do both gym and spinning to increase her options? Just because we are told about two options does NOT mean that those options are mutually exclusive. 

 

5

IDENTIFY THE FLAW:

In a survey of voters who intend to vote by absentee ballot in the upcoming presidential election, 55% said that they will vote for Darren, whereas only 45% said that they will vote for Halley. So, Darren will probably win the election.

SAMPLING FALLACY (UNREPRESENTATIVE)

The survey involved voters who intend to vote by absentee ballot...but how representative are these voters of the general voting population? We have no idea. Maybe the absentee voters are much younger, or older, or richer, or more into certain political causes than the voters who are going to vote in person? So this survey might be unrepresentative, which means it doesn't provide adequate support for the conclusion that Darren will probably win.

6

IDENTIFY THE FLAW:

Randy's favorite foods include chocolate, pizza, ice cream, and sushi. So, he's going to enjoy the meal I'm making for him: pizza topped with sushi, chocolate, and ice cream.

PART-TO-WHOLE FALLACY

Things that are true about the individual parts of a group do not have to be true of the group. Just because Randy lilkes each of the foods individually does not mean that he likes them all together. Maybe some of the flavors of sushi and chocolate clash and Randy won't like the combination? 

7

IDENTIFY THE FLAW:

Rainier University's economics department produces the most innovative scholarship in the its field. Thus, each of the professors in the department must be an extremely innovative scholar.

WHOLE-TO-PART FALLACY

A quality possessed by the whole does not have to be shared by the individual parts. Maybe the department's innovative scholarship is produced by just a small portion of the professors; not every professor needs to be extremely innovative. Or maybe the professors, together, produce innovative work, but each one by themselves is not necessarily extremely innovative. 

8

IDENTIFY THE FLAW:

Despite numerous attempts to locate living dinosaurs, researchers have yet to produce one shred of evidence that some dinosaurs have survived in remote parts of the world. Thus, we can be sure that there are currently no living dinosaurs. 

ABSENCE OF EVIDENCE (UNPROVEN VS. UNTRUE)

Just because there's no evidence of a claim does not mean that claim is false. Even though we haven't found evidence that dinosaurs still exist, it's still theoretically possible that they exist. Maybe we just haven't been searching in the right places for the evidence?

9

IDENTIFY THE FLAW:

The number of people who suffer from tuberculosis in the United States today is over ten times the number who suffered from the disease in the United States in 1800. Thus, the rate of tuberculosis in the United States has increased dramatically since that year.

NUMBER VS. RATE

The absolute number of people who have tuberculosis may have gone up, but in order to calculate the rate we have to divide that number by the overall population. Since there are a lot more ten times the number of people in the United States today compared to 1800, it's actually possible that the rate of tuberculosis has gone down. So remember, the absolute number of something does not, by itself, tell you anything about the overall rate or the chance of that thing occurring.

10

IDENTIFY THE FLAW:

TeethBrite is selling twice as many toothbrushes this year as it sold last year. Thus, their share of the toothbrush market must have increased.

PERCENT VS. AMOUNT

The amount/number of toothbrushes sold by Teethbrite has gone up...but that doesn't mean that Teethbrite has a higher % of the toothbrush market. Maybe the entire market is larger and everyone is just selling more toothbrushes. In that case, Teethbrite's market share might be the same, or have even gone down, despite selling more toothbrushes.

11

IDENTIFY THE FLAW:

Many people who volunteer for public interest organizations might be doing so only to portray themselves as morally virtuous. Thus, these people are volunteering for a selfish reason.

LOGICAL FORCE FLAW

A premise cannot support a conclusion that is expressed with a greater logical force. Here, the premise is that the people "might" be trying to portray themselves as morally virtuous. But the conclusion assumes that these people "are" in fact doing so. However, "might" cannot support anything stronger than "might".

12

IDENTIFY THE FLAW:

On average, people who go to sleep and wake up earlier are more successful in their careers than those who go to sleep and wake up later. So, if you want to be more successful, you should try to sleep and wake up earlier.

CORRELATION TO CAUSE

Sure, there's a correlation between sleeping/waking earlier and success. But who's to say the the success is *caused* by the sleeping/waking time? Maybe people who are more successful find it easier to fall asleep and wake up earlier because they're not as stressed or worried about their lives? Maybe there's a third factor that explains the situation, perhaps certain people have genes that make them sleep/wake up earlier and that make them more hard-working and successful? The point is correlation does NOT prove causation.

 

13

IDENTIFY THE FLAW:

PectoGlisten is an easy-to-apply chest spray that guarantees users' pectoral muscles will shine.  The next time you go to the neighborhood pool, you can conclude that anyone whose pecs are shining must have used PectoGlisten.

CONFUSING SUFFICIENT AND NECESSARY

PectoGlisten is sufficient for getting shiny pecs...but that doesn't mean it's necessary. Maybe there are other ways to get a shiny chest? The author of this argument mistakenly believed that PectoGlisten was necessary.

14

IDENTIFY THE FLAW:

Ryu will bring an umbrella to work if she believes that it will rain in the evening today . Since it is guaranteed to rain in the evening today, Ryu will bring an umbrella to work.

PERCEPTION VS. REALITY

One of the premises tells us that it will in fact rain today. But does that mean Ryu believes that it will rain today? He might not be aware of the fact that it will rain, even if it's true. On the LSAT, and in real life, we can't assume that just because something is true, people must be aware that it's true.

 

15

IDENTIFY THE FLAW:

Being successful in life requires hard work. How do we know this is true? Because all successful people must have worked hard in order to achieve their success.

CIRCULAR REASONING

If we want to make a good argument, our conclusion should not just be a restatement of one of our premises. It's not persuasive to just assert that a claim is true because...that claim is true. Here, the conclusion that being successful requires hard work is supported by the claim that all successful people must have worked hard. But the conclusion and its premise are just different ways to say the same thing.

16

IDENTIFY THE FLAW:

It has been established that neither Rina nor Tanner murdered the CEO. Since the only other suspect that the police have identified is Warren, Warren must be the murderer.

EXCLUSIVITY (FAILS TO EXCLUDE ALTERNATIVES)

When an argument proceeds by eliminating options to get down to one choice, we have to know that those options were the only ones available. Here, what if the murderer is someone who isn't currently a suspect? Maybe the police just haven't found the right person yet? This argument fails to exclude alternatives to Rina, Tanner, and Warren.

17

IDENTIFY THE FLAW:

New York City is the safest major city in the United States. Thus, it is safe.

ABSOLUTE VS. RELATIVE

Some qualities are relative, meaning they are about how one thing compares to another. But a relative quality is different from an absolute quality, which doesn't depend on a comparison. Here, "safest" is a relative term; it's about how safe NYC is compared to other major cities. But that doesn't allow us to conclude that NYC is "safe"; NYC could still be very dangerous, even if it's safer than other major cities.

18

IDENTIFY THE FLAW:

Some people argue that we should not eat meat on the grounds that animals have the right not be killed for food. However, this argument relies on a completely absurd understanding of rights. Animals do not have rights. Therefore, people should eat meat.

WEAK ARGUMENT FALLACY

Even if someone else's argument has a premise that's false or is making an assumption that's questionable, that doesn't mean the argument's conclusion is false. Here, the argument of "some people" relies on the grounds that animals have the right not to be killed for food. The author of this passage says that premise is wrong; in fact, animals do not have rights. However, even if animals don't have rights, that doesn't establish that people should eat meat. Maybe there could be other reasons people should not eat meat?