Journalist: Contrary to popular opinion, it is more dangerous for an individual to drive during the day than during the night. A recent study found that in each of the last ten years, the number of traffic accidents that resulted in death was greater during the day than during the night.

Summarize Argument: Phenomenon-Hypothesis
The journalist hypothesizes that driving during the day is more dangerous than driving at night. She supports this by citing a study showing that the number of fatal traffic accidents was higher during the day than at night in each of the last ten years.

Notable Assumptions
The journalist assumes that the number of fatal accidents is the best indicator of driving danger and directly translates to it being more dangerous to drive during the day. She doesn’t consider other factors like traffic volume, non-fatal accidents, or other potential risks.

A
Only during the day are there more unsafe than safe vehicles on the road.
This strengthens the hypothesis by providing an additional reason why daytime driving is more dangerous and nighttime driving is safer. If there are only more unsafe vehicles during the day, then there are more safe drivers than unsafe drivers at night.
B
There is decreased law enforcement presence during the day.
This strengthens the hypothesis by providing an additional reason why daytime driving is more dangerous. Decreased law enforcement during the day may increase the likelihood of reckless drivers, speeding, and other risk factors.
C
Persons drive more cautiously during the night than during the day.
This strengthens the hypothesis by providing an additional reason why daytime driving is more dangerous and nighttime driving is safer. Because people drive more cautiously during the night than during the day, daytime driving is more dangerous.
D
The number of travelers per vehicle has increased over the past ten years.
Irrelevant— we don’t know whether this applies to vehicles traveling in the day, at night, or both. We also don’t know whether having more travelers per vehicle makes driving more or less dangerous. So, (D) doesn’t strengthen the argument.
E
Persons drive faster during the day than during the night.
This strengthens the hypothesis by providing an additional reason why daytime driving is more dangerous and nighttime driving is safer— because people drive faster during the day than at night.

1 comment

This is a Flaw/Descriptive Weakening question.

The argument takes on a form that we’ve seen plenty before. It says that the Swahili civilization built a particular kind of tomb. Such tombs were widespread among the Oromo civilization and unknown among any other civilization that the Swahili had contacted. From these premises, the argument draws the conclusion that the Swahili were influenced by the Oromo.

Okay, that’s a bold assertion on thin evidence. All we know is that the Oromo also built these tombs. That doesn’t mean that the Swahili imitated the Oromo. It’s certainly possible. But it’s also possible that the Oromo imitated the Swahili. That’s an alternative hypothesis. To discriminate between them, we need more information. Maybe there’s some evidence consistent with one hypothesis but inconsistent with the other. Maybe there’s information about chronology. Who built these tombs first? That’d be a clue about who’s the influencer and who’s the imitator.

Answer Choice (A) says that the argument fails to adequately address the possibility that the Oromo used these structures as something other than tombs. That’s true. But that’s not where the argument is weak. Even if we stipulate that the Oromo used these structures as tombs, the argument still suffers from its causal weaknesses.

Answer Choice (B) says that the argument concludes that the first event caused the second event simply because the first event occurred earlier. If only! Information about the Oromo being first to build these tombs would be really helpful in establishing the conclusion that the Swahili learned from the Oromo. There is no such information so (B) is descriptively inaccurate.

Answer Choice (C) says that the argument draws a restricted conclusion from premises that provide strong support for a much broader conclusion. Uh, come again? (C) thinks this argument could have drawn a broader conclusion? And that the main weakness of the reasoning is that the actual conclusion didn’t go far enough? That’s crazy. The argument has a hard enough time supporting its existing conclusion. It won’t be helped if we swap that conclusion out for an even heavier, more expansive conclusion. I think (C) is picking up on the “to some extent” qualifier in the conclusion. Like, (C) is saying that’s what makes the argument vulnerable, that it should have just come out with a more forceful conclusion. But that misses the point. Toggling the strength of the causal arrow up or down is irrelevant. The problem with this argument is that the causal hypothesis in the conclusion is merely one of many.

Answer Choice (D) says that the argument assumes there was no third civilization responsible for creating the first tombs of the kind found in both the Oromo and Swahili cultures. This is a very attractive trap. It describes a cookie-cutter flaw that we’ve seen so many times in other Flaw questions. The problem is that the argument doesn’t make this assumption. The premises already established that the Swahili had no contact with any other civilization that built such tombs. That precludes the hypothesis that a third civilization was the true creators of these tombs and they were the OG influencers. That couldn’t have happened because the Swahili had no contact with any other civilization that built these tombs except the Oromo. Since this third culture hypothesis is already precluded, the argument doesn’t have to assume anything about whether they first created these tombs. It wouldn’t matter either way. Imagine if it were true that some third culture created the tombs. So what? They’re halfway across the continent and the Swahili didn’t have any contact with them. So if the Swahili learned it from anyone, it would still have to be from the Oromo. (D) is descriptively inaccurate. The argument makes no such assumption because the argument doesn’t have to. The alternative hypothesis that (D) is concerned with was already precluded by the premises.

Correct Answer Choice (E) says that the argument assumes that the Oromo built their tombs earlier than the Swahili did. Yes, that’s definitely an assumption that the argument makes. In order for the Oromo to have influenced the Swahili, the Oromo had to have done it first. If the Swahili got there first, then perhaps it’s the Oromo who were influenced by the Swahili. (E) is descriptively accurate. More than that, (E) is why the argument is weak. There is no information about who got there first. Without that information, we cannot say whether the Oromo as influencer hypothesis or the Swahili as influencer hypothesis is more likely to be true. This is precisely where the argument is most vulnerable to criticism.


21 comments

This is a Flaw/Descriptive Weakening question.

The argument takes on a form that we’ve seen plenty before. It says that the Swahili civilization built a particular kind of tomb. Such tombs were widespread among the Oromo civilization and unknown among any other civilization that the Swahili had contacted. From these premises, the argument draws the conclusion that the Swahili were influenced by the Oromo.

Okay, that’s a bold assertion on thin evidence. All we know is that the Oromo also built these tombs. That doesn’t mean that the Swahili imitated the Oromo. It’s certainly possible. But it’s also possible that the Oromo imitated the Swahili. That’s an alternative hypothesis. To discriminate between them, we need more information. Maybe there’s some evidence consistent with one hypothesis but inconsistent with the other. Maybe there’s information about chronology. Who built these tombs first? That’d be a clue about who’s the influencer and who’s the imitator.

Answer Choice (A) says that the argument fails to adequately address the possibility that the Oromo used these structures as something other than tombs. That’s true. But that’s not where the argument is weak. Even if we stipulate that the Oromo used these structures as tombs, the argument still suffers from its causal weaknesses.

Answer Choice (B) says that the argument concludes that the first event caused the second event simply because the first event occurred earlier. If only! Information about the Oromo being first to build these tombs would be really helpful in establishing the conclusion that the Swahili learned from the Oromo. There is no such information so (B) is descriptively inaccurate.

Answer Choice (C) says that the argument draws a restricted conclusion from premises that provide strong support for a much broader conclusion. Uh, come again? (C) thinks this argument could have drawn a broader conclusion? And that the main weakness of the reasoning is that the actual conclusion didn’t go far enough? That’s crazy. The argument has a hard enough time supporting its existing conclusion. It won’t be helped if we swap that conclusion out for an even heavier, more expansive conclusion. I think (C) is picking up on the “to some extent” qualifier in the conclusion. Like, (C) is saying that’s what makes the argument vulnerable, that it should have just come out with a more forceful conclusion. But that misses the point. Toggling the strength of the causal arrow up or down is irrelevant. The problem with this argument is that the causal hypothesis in the conclusion is merely one of many.

Answer Choice (D) says that the argument assumes there was no third civilization responsible for creating the first tombs of the kind found in both the Oromo and Swahili cultures. This is a very attractive trap. It describes a cookie-cutter flaw that we’ve seen so many times in other Flaw questions. The problem is that the argument doesn’t make this assumption. The premises already established that the Swahili had no contact with any other civilization that built such tombs. That precludes the hypothesis that a third civilization was the true creators of these tombs and they were the OG influencers. That couldn’t have happened because the Swahili had no contact with any other civilization that built these tombs except the Oromo. Since this third culture hypothesis is already precluded, the argument doesn’t have to assume anything about whether they first created these tombs. It wouldn’t matter either way. Imagine if it were true that some third culture created the tombs. So what? They’re halfway across the continent and the Swahili didn’t have any contact with them. So if the Swahili learned it from anyone, it would still have to be from the Oromo. (D) is descriptively inaccurate. The argument makes no such assumption because the argument doesn’t have to. The alternative hypothesis that (D) is concerned with was already precluded by the premises.

Correct Answer Choice (E) says that the argument assumes that the Oromo built their tombs earlier than the Swahili did. Yes, that’s definitely an assumption that the argument makes. In order for the Oromo to have influenced the Swahili, the Oromo had to have done it first. If the Swahili got there first, then perhaps it’s the Oromo who were influenced by the Swahili. (E) is descriptively accurate. More than that, (E) is why the argument is weak. There is no information about who got there first. Without that information, we cannot say whether the Oromo as influencer hypothesis or the Swahili as influencer hypothesis is more likely to be true. This is precisely where the argument is most vulnerable to criticism.


25 comments

This is a Main Point question.

The argument in the stimulus contains a lot of complications. First we get the context. Then we see the word “however,” which introduces the transition from context to argument. The argument itself contains a sub-premise supporting a major premise supporting the main conclusion. And on top of all that, it uses the contrapositive argument form.

The context tells us that radioactive elements may have been created when the universe began. The next sentence says “however,” which indicates the transition over to argument, followed by “even if that were true,” which indicates that the information in the context is “throwaway.” We don't really care whether radioactive elements were created at the beginning of the universe, because what we really care about is that radioactive elements are still being created today. And that's the main conclusion. How do we know that? Well, it's the rest of the stimulus that provides the support. Let's skip the next sentence and instead jump to the last sentence, which contains the contrapositive argument. The sufficient condition is introduced by the word “if.” If no new radioactive elements have been created after the universe began, then there would be almost no radioactive elements left in the universe today. Next, we fail the necessary condition. There is an abundance of radioactive elements in the universe today. This allows us to contrapose on the conditional and draw the failure of the sufficient condition as the conclusion. New radioactive elements have been created since the universe began. Okay, so that's good but it's still been billions (13.7) of years since the universe began. How do we know that new radioactive elements are still being created today?

That's where the middle sentence comes in. That sentence does two things. One is that it explains why we should believe the conditional to begin with. It’s support. If you are skeptical about the if-then statement, you can consult this middle sentence. The reason why if no new radioactive elements are being constantly created, then we would run out of radioactive elements is explained by the middle sentence. It's because radioactive elements are really unstable so within a few million years all of them would've disappeared. That's the minor premise that acts as support for the major conditional premise. The other is precisely to fix the timing issue. It's saying that radioactive elements only live for a few million years so the ones we're seeing today can't be that old (in universe time), like at oldest, it's only a few million years old. That's still not today, but it does bring it billions of years closer to today.

Answer Choice (A) would be the correct answer choice to an MSS question. It says that any radioactive element created at the beginning of the universe has probably decayed into other nonradioactive elements. This is supported by the minor premise, which sets a time limit of at most a few million years for decay.

Correct Answer Choice (B) is the most accurate paraphrasing of the main conclusion.

Answer Choice (C) is the major conditional premise.

Answer Choice (D) is the context of the argument.

Answer Choice (E) is the middle statement, which plays the role of minor premise (explaining the major conditional premise) and major premise (fixing the timing issue).


1 comment

Radioactive elements may have been created when the universe began. However, even if this occurred, these elements are clearly still being created in the universe today. Radioactive elements are unstable, so most of them decay within at most a few million years into other, nonradioactive elements. So, if no new radioactive elements had been created after the universe began, almost no radioactive elements would be left in the universe today, but there is an abundance of such elements.

Summarize Argument
The author concludes that radioactive elements are still being created in the universe. This conclusion is based on the contrapositive of a conditional statement offered as support. If no new radioactive elements had been created after the universe began, then there would be almost no radioactive elements left in the universe today. But we know there’s a large amount of such elements today.

Identify Conclusion
The conclusion is the author’s assertion that radioactive elements are still being created today: “[T]hese elements are clearly still being created in the universe today.”

A
Any radioactive elements created when the universe began have probably decayed into other, nonradioactive elements.
This is an inference we can draw from the third sentence. Based on this, the author believes that if no radioactive elements had been created after the universe began, we wouldn’t find many radioactive elements today. This conditional is used to support the author’s conclusion.
B
Radioactive elements are being created in the universe today.
This is a paraphrase of the author’s conclusion.
C
If no new radioactive elements had been created after the universe began, almost no radioactive elements would be left in the universe today.
This is a subsidiary conclusion based on the premise that most radioactive elements decay within a few million years. The author uses this conditional to conclude that radioactive elements were created after the universe began.
D
It is possible that radioactive elements were created when the universe began.
This is context. The author’s argument concerns whether there were radioactive elements created after the universe began.
E
Due to their instability, most of the universe’s radioactive elements decay within at most a few million years into other, nonradioactive elements.
This is a premise.

2 comments

This is a Strengthen question.

The difficulty of this question mostly comes from the attractiveness of the wrong answers and a complication to an otherwise simple argument form. Stripping the wrong answers away and simplifying the conclusion reveal a common recurring pattern. The stimulus contains a correlation premise followed by a causal conclusion. The correct answer choice precludes an alternate hypothesis. But like I said, the actual argument is more complex and the presence of four very attractive wrong answers also works to obscure the pattern.

The stimulus starts with a dentist reporting data from five studies. The data reveals that in Europe, the proportion of children with bad teeth is lower than in the United States. It also tells us that in Europe, water is not fluoridated, whereas in the United States, water is fluoridated. As you can see, this is the classic setup where a phenomenon is presented that correlates with another phenomenon. And we’re invited to infer a causal relationship. Naturally, we want to explain why children in Europe have fewer teeth problems. The stimulus conveniently tells us that in Europe, water is not fluoridated, whereas in the United States, water is.

A simpler version of this argument could have gone like this: Therefore, fluoridated water causes teeth problems for children. This would be the classic A (fluoridated water) is correlated with B (teeth issues), therefore A causes B.

The actual argument is a bit more sophisticated and relies implicitly on the contrapositive argument form. The assumption is that if fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water. The data showed just the opposite. So therefore, the actual conclusion states that fluoridated water doesn’t prevent teeth issues.

The reason why the reasoning is vulnerable is the same reason why, in general, arguments of this form fail. Bad causal assumptions. “If fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water” would be true only if all other causal factors have been controlled for. Clearly, that didn’t happen. The data did not come from anything resembling an ideal experiment. Rather, it came from observational studies. That means whatever differences between Europe and the United States that may be causally relevant to the health of children's teeth are acting on the outcomes.

Think about this in terms of Weaken. If we wanted to expose the vulnerability of the reasoning, we’d simply point out any causal influence that wasn’t controlled for that could have affected dental health. For example, we could have stipulated that in the United States, children eat a lot more candy, which rots teeth. If that's true, then we found an explanation of the difference in dental health between Europe and the United States that doesn’t suggest that fluoridated water is ineffective. Rather, it may well be that fluoridated water actually protects teeth but that preventative causal impact is being overwhelmed by the decaying causal impact of sugars. Kids in the United States have teeth issues in spite of fluoridated water.

If stipulating this to be true weakens the argument, then precluding it strengthens the argument. This is what Correct Answer Choice (E) does. It tells us that the diets of children in the United States are not generally worse for teeth than those of children in Europe. This generally precludes the entire class of food-related explanations of the difference in dental health of which my sugar explanation was just one specific example. By precluding the entire class of explanations, (E) does not prove the hypothesis to be true. But (E) does strengthen the argument by making the hypothesis just a bit more probable.

Interestingly, had the argument been simpler, that is, had the conclusion simply said that fluoridated water causes teeth problems for children, (E) would still work. In fact, it’d be even more obvious that (E) fit the cookie-cutter mold of precluding an alternative explanation.

A note about strategy under timed conditions. I tend to remind you that given the nature of strengthening and weakening questions that deal in a phenomenon hypothesis, it is difficult to anticipate what the correct answer choice will say. That is true in this question as well, which is why, in general, the best strategy is to use POE even though you’d be exposed to the mischief of the wrong answers.

Answer Choice (B) says nearly all dentists in the United States use dental treatments involving the application of fluoride directly to tooth surfaces. (B) can be eliminated simply by recognizing that the causal direction of fluoride pushes in the opposite direction. The conclusion says that fluoride doesn’t benefit dental health yet (B) implies, by appeal to relevant authority, that fluoride does benefit dental health. Clearly, this does not strengthen the argument. But it also doesn't weaken the argument either if you look closer at the details. Even if it's true that fluoride, when directly applied by dentists to tooth surfaces, is effective for treating dental problems, it still may be true that fluoride in water has no effect on protecting teeth.

Answer Choice (D) says that, on average, children in Europe receive more frequent dental checkups than children in the United States. Rather than precluding an explanation of the differences in dental health, (D) seems to be introducing one. If children in Europe differ from children in the United States in that European children receive more frequent preventative care, then that explains why they have better teeth. This is just like when we contemplated diet as the alternative explanation. If children in Europe had a healthier diet for their teeth or had more frequent preventative care for their teeth, the fact that they have healthier teeth may have nothing to do with the presence or absence of fluoride in their water. This would weaken the argument.

Answer Choice (A) says that toothpaste containing fluoride is widely available in both the United States and Europe. (A) is attractive because in form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. The problem, however, is in order for (A) to be preclusive, it needs some questionable assumptions.

First, notice that we are being baited to assume that wide availability implies equal usage in children. That is a very specific and arbitrary assumption. Wide availability of fluoride toothpaste in and of itself doesn't bear on the issue. What we actually care about is whether children in Europe and the United States use that widely available fluoride toothpaste to a comparable degree. (A) is silent about that phenomenon.

Second, even if we fixed this first problem, (A) still has another subtler problem. Imagine if the answer said that the use of fluoride toothpaste is comparable for children in the United States and Europe. That would seem to preclude the possibility that European children use more fluoride toothpaste than their American counterparts, and it's this extra usage that accounts for their healthier teeth. Yet this reasoning requires fluoride to be good for teeth when in toothpaste, yet useless for teeth when in water. That's an unwarranted assumption. It's not impossible, but it hardly seems reasonable to assume without evidence.

Answer Choice (C) says dental hygiene is typically taught in elementary school in both Europe and the United States. (C) is attractive in the same way that (A) is attractive. In form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. In this case, the potential causal factor is whether dental hygiene is taught in school. And (C) precludes the phenomenon where dental hygiene is only taught in elementary school in Europe and not the United States. The problem is that we don't care much about precluding this phenomenon. Because even if dental hygiene is typically taught only in elementary schools in Europe and not the United States, a lot of other causal assumptions need to be supplied in order for the observed difference in dental health to be explained. First, we need to assume that children enact dental hygiene behaviors that they learn in school because otherwise the mere instruction would have no causal impact on their dental health. Second, we also need to assume that just because American children don't learn dental hygiene at school, they don't learn it at all. That seems highly unlikely, since if they're not learning it in school, then parents would have extra incentive to teach dental hygiene at home.

Notice how Correct Answer Choice (E) doesn't suffer from the need to fill in these causal gaps with questionable assumptions. If the diets of children in the United States were generally worse for dental health, then that explains the observed difference in dental health.


20 comments

Dentist: Five recently conducted studies all show that the proportion of children with decayed, missing, or filled teeth is lower in Europe, where water is not fluoridated, than in the United States, where it is. This is convincing evidence that fluoridation of water does not have a substantial tendency to prevent tooth decay.

Summarize Argument: Phenomenon-Hypothesis
The dentist hypothesizes that fluoridated water doesn't significantly prevent tooth decay. She supports this by citing recent studies showing that in Europe, where water isn't fluoridated, the rate of tooth decay in children is lower than in the U.S., where water is fluoridated.

Notable Assumptions
The dentist overlooks other factors, like diet, oral hygiene, or healthcare access, that could affect tooth decay rates. She assumes water fluoridation doesn't prevent decay without considering that decay rates might be different to begin with.

A
Toothpaste containing fluoride is widely available in both the United States and Europe.
Just because fluoride toothpaste is widely available does not mean that children are using it. (A) doesn’t help to confirm the hypothesis that fluoridated water fails to prevent tooth decay.
B
Nearly all dentists in the United States use dental treatments involving the application of fluoride directly to tooth surfaces.
Irrelevant— (B) does not imply that fluoride is therefore ineffective at preventing decay. We don’t know whether most children in the U.S. visit the dentist or whether all European dentists also apply fluoride to tooth surfaces.
C
Dental hygiene is typically taught in elementary school in both Europe and the United States.
Like (A), just because dental hygiene is taught in Europe and the U.S. doesn't mean that children then practice it. This doesn’t help to show that the fluoridation of water is the main difference in dental hygiene between American and European children.
D
On average, children in Europe receive dental checkups more frequently than children in the United States.
This weakens the argument by providing an alternative hypothesis to explain the differing rates of tooth decay. If European children receive more frequent dental care, it makes sense that they also have lower rates of tooth decay.
E
The diets of children in the United States are not generally worse for teeth than those of children in Europe.
This strengthens the argument by eliminating an alternative hypothesis. If the diets of children in the United States are not worse for teeth, then diet is unlikely to be the cause of their tooth decay.

This is a Strengthen question.

The difficulty of this question mostly comes from the attractiveness of the wrong answers and a complication to an otherwise simple argument form. Stripping the wrong answers away and simplifying the conclusion reveal a common recurring pattern. The stimulus contains a correlation premise followed by a causal conclusion. The correct answer choice precludes an alternate hypothesis. But like I said, the actual argument is more complex and the presence of four very attractive wrong answers also works to obscure the pattern.

The stimulus starts with a dentist reporting data from five studies. The data reveals that in Europe, the proportion of children with bad teeth is lower than in the United States. It also tells us that in Europe, water is not fluoridated, whereas in the United States, water is fluoridated. As you can see, this is the classic setup where a phenomenon is presented that correlates with another phenomenon. And we’re invited to infer a causal relationship. Naturally, we want to explain why children in Europe have fewer teeth problems. The stimulus conveniently tells us that in Europe, water is not fluoridated, whereas in the United States, water is.

A simpler version of this argument could have gone like this: Therefore, fluoridated water causes teeth problems for children. This would be the classic A (fluoridated water) is correlated with B (teeth issues), therefore A causes B.

The actual argument is a bit more sophisticated and relies implicitly on the contrapositive argument form. The assumption is that if fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water. The data showed just the opposite. So therefore, the actual conclusion states that fluoridated water doesn’t prevent teeth issues.

The reason why the reasoning is vulnerable is the same reason why, in general, arguments of this form fail. Bad causal assumptions. “If fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water” would be true only if all other causal factors have been controlled for. Clearly, that didn’t happen. The data did not come from anything resembling an ideal experiment. Rather, it came from observational studies. That means whatever differences between Europe and the United States that may be causally relevant to the health of children's teeth are acting on the outcomes.

Think about this in terms of Weaken. If we wanted to expose the vulnerability of the reasoning, we’d simply point out any causal influence that wasn’t controlled for that could have affected dental health. For example, we could have stipulated that in the United States, children eat a lot more candy, which rots teeth. If that's true, then we found an explanation of the difference in dental health between Europe and the United States that doesn’t suggest that fluoridated water is ineffective. Rather, it may well be that fluoridated water actually protects teeth but that preventative causal impact is being overwhelmed by the decaying causal impact of sugars. Kids in the United States have teeth issues in spite of fluoridated water.

If stipulating this to be true weakens the argument, then precluding it strengthens the argument. This is what Correct Answer Choice (E) does. It tells us that the diets of children in the United States are not generally worse for teeth than those of children in Europe. This generally precludes the entire class of food-related explanations of the difference in dental health of which my sugar explanation was just one specific example. By precluding the entire class of explanations, (E) does not prove the hypothesis to be true. But (E) does strengthen the argument by making the hypothesis just a bit more probable.

Interestingly, had the argument been simpler, that is, had the conclusion simply said that fluoridated water causes teeth problems for children, (E) would still work. In fact, it’d be even more obvious that (E) fit the cookie-cutter mold of precluding an alternative explanation.

A note about strategy under timed conditions. I tend to remind you that given the nature of strengthening and weakening questions that deal in a phenomenon hypothesis, it is difficult to anticipate what the correct answer choice will say. That is true in this question as well, which is why, in general, the best strategy is to use POE even though you’d be exposed to the mischief of the wrong answers.

Answer Choice (B) says nearly all dentists in the United States use dental treatments involving the application of fluoride directly to tooth surfaces. (B) can be eliminated simply by recognizing that the causal direction of fluoride pushes in the opposite direction. The conclusion says that fluoride doesn’t benefit dental health yet (B) implies, by appeal to relevant authority, that fluoride does benefit dental health. Clearly, this does not strengthen the argument. But it also doesn't weaken the argument either if you look closer at the details. Even if it's true that fluoride, when directly applied by dentists to tooth surfaces, is effective for treating dental problems, it still may be true that fluoride in water has no effect on protecting teeth.

Answer Choice (D) says that, on average, children in Europe receive more frequent dental checkups than children in the United States. Rather than precluding an explanation of the differences in dental health, (D) seems to be introducing one. If children in Europe differ from children in the United States in that European children receive more frequent preventative care, then that explains why they have better teeth. This is just like when we contemplated diet as the alternative explanation. If children in Europe had a healthier diet for their teeth or had more frequent preventative care for their teeth, the fact that they have healthier teeth may have nothing to do with the presence or absence of fluoride in their water. This would weaken the argument.

Answer Choice (A) says that toothpaste containing fluoride is widely available in both the United States and Europe. (A) is attractive because in form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. The problem, however, is in order for (A) to be preclusive, it needs some questionable assumptions.

First, notice that we are being baited to assume that wide availability implies equal usage in children. That is a very specific and arbitrary assumption. Wide availability of fluoride toothpaste in and of itself doesn't bear on the issue. What we actually care about is whether children in Europe and the United States use that widely available fluoride toothpaste to a comparable degree. (A) is silent about that phenomenon.

Second, even if we fixed this first problem, (A) still has another subtler problem. Imagine if the answer said that the use of fluoride toothpaste is comparable for children in the United States and Europe. That would seem to preclude the possibility that European children use more fluoride toothpaste than their American counterparts, and it's this extra usage that accounts for their healthier teeth. Yet this reasoning requires fluoride to be good for teeth when in toothpaste, yet useless for teeth when in water. That's an unwarranted assumption. It's not impossible, but it hardly seems reasonable to assume without evidence.

Answer Choice (C) says dental hygiene is typically taught in elementary school in both Europe and the United States. (C) is attractive in the same way that (A) is attractive. In form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. In this case, the potential causal factor is whether dental hygiene is taught in school. And (C) precludes the phenomenon where dental hygiene is only taught in elementary school in Europe and not the United States. The problem is that we don't care much about precluding this phenomenon. Because even if dental hygiene is typically taught only in elementary schools in Europe and not the United States, a lot of other causal assumptions need to be supplied in order for the observed difference in dental health to be explained. First, we need to assume that children enact dental hygiene behaviors that they learn in school because otherwise the mere instruction would have no causal impact on their dental health. Second, we also need to assume that just because American children don't learn dental hygiene at school, they don't learn it at all. That seems highly unlikely, since if they're not learning it in school, then parents would have extra incentive to teach dental hygiene at home.

Notice how Correct Answer Choice (E) doesn't suffer from the need to fill in these causal gaps with questionable assumptions. If the diets of children in the United States were generally worse for dental health, then that explains the observed difference in dental health.


28 comments

This is a Main Conclusion question.

I think a little bit of economics knowledge is helpful for this question. The stimulus says railroads rely increasingly on automation. And since fewer railroad workers are needed (premise), operating costs have been reduced (conclusion). When an industry increasingly relies on automation, it means it needs fewer workers, right? And as a result, operating costs have been reduced. It is cheaper to operate railroads now. Let’s read on to see if this is the main conclusion or a sub-conclusion.

The stimulus then says this means that we can expect the volume of freight shipped by rail to grow, with “this” referring to the fact that it is cheaper to operate railroads. “Operating costs have been reduced” now sounds like a sub-conclusion. Why should I believe that railway shipping volume will grow? Because railway is cheaper. People are now going to use more of it. This is not an airtight argument. There are multiple assumptions at play. One is that because operating costs are reduced, price will be reduced. Another is that because price is reduced, demand will increase. Noted, but we're just looking for the main conclusion here.

Now the last sentence says that the chief competitor of railway shipping is shipping by truck, and no reduction in operating costs is predicted for the trucking industry. If we make the same two assumptions again here, that means prices for trucking are not going to change. And because trucks are railway’s competitors, that means relative to trucks, railway's price is cheaper. If we assume that relative costs affect demand, then that's also support for the conclusion that the volume of freight shipped by rail will grow. So that's the main conclusion.

If this were a Weaken or Strengthen question, then we would definitely latch onto any of those assumptions. But this is just an MC question.

Correct Answer Choice (A) is the correct paraphrasing. The volume of freight shipped by rail can be expected to increase.

Answer Choice (B) could be correct in “inference from the author's perspective” questions in Reading Comprehension that ask for the claim the author would most likely agree with. (B) says increasing reliance on automation means that fewer railroad workers are needed. While this is definitely implied in the first two sentences of the stimulus, it is not the main conclusion.

Answer Choices (C) and (E) say no reduction in operating cost is predicted for the trucking industry, and that the chief competitor for railway shipping is shipping by truck. Both of these are true claims, but neither is the conclusion.

We can confirm this because neither is supported in any way. For (E), what if I believed that the chief competitor of railroads is cargo donkeys? The author does not try to convince me that I am wrong. (E) is just a take it or leave it, a premise. Conclusions are not take it or leave it. They give us reasons why we should believe.

The same goes for (C). Maybe I believe that there will be a reduction in operating costs for the trucking industry. Have you not heard of Tesla trucks? They are supposed to be way cheaper. Again, the author would not try to convince me otherwise, and that is not the characteristic of a conclusion.

Answer Choice (D) says operating costs for railroads have been reduced as a result of increased reliance on automation. This is just the argument that produces the sub-conclusion/major premise, which then in turn supports the main conclusion.


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Railroads rely increasingly on automation. Since fewer railroad workers are needed, operating costs have been reduced. This means that we can expect the volume of freight shipped by rail to grow. The chief competitor of railway shipping is shipping by truck, and no reduction in operating costs is predicted for the trucking industry.

Summarize Argument
The author concludes that we can expect the volume of freight shipped by rail to increase. This is because railroads have had reduced operating costs, whereas the main competitor to railway shipping (trucking) is not predicted to have reduced operating costs.

Identify Conclusion
The conclusion is the author’s prediction for what will happen to the volume of rail freight shipping: “[W]e can expect the volume of freight shipped by rail to grow.”

A
The volume of freight shipped by rail can be expected to increase.
This is a restatement of the conclusion.
B
Increasing reliance on automation means that fewer railroad workers are needed.
This is part of the support. Because fewer railroad workers are needed, the railroad industry has reduced operating costs. The author uses this support a prediction about an increase in the volume of rail freight.
C
No reduction in operating costs is predicted for the trucking industry.
This is a premise. The author uses the lack of reduced operating costs in a competitor industry to support a prediction about the increase in rail freight.
D
Operating costs for railroads have been reduced as a result of increased reliance on automation.
This is part of the support. Because of the reduced operating costs, the author predicts an increase in rail freight.
E
The chief competitor of railway shipping is shipping by truck.
This is a premise. The author points out that rail’s chief competitor isn’t predicted to have reduced operating costs to support the prediction that rail freight volume will increase.

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