A
A lack of regular exercise is one cause of lethargy in North Americans.
B
High consumption of fast food is a health risk only when combined with a lack of regular exercise.
C
The researcher’s data show that the consumption of fast food is not the main cause of poor health in North Americans.
D
The lethargy studies failed to consider one probable cause of lethargy.
E
The researcher’s conclusion was not adequately justified by the lethargy studies.
This is a Must Be True question.
This question tests your ability to manipulate grammar to reveal underlying logical relationships between sets. In particular, we are dealing with sets of intersections and supersets and subsets.
The stimulus states that if a belief is based on information from a reliable source, then it is reasonable to maintain that belief. This is a standard conditional claim using the “if... then...” formulation. Let's kick the idea of “a belief” up into the domain. This will simplify the analysis. You wouldn't know at this moment to do this. You have to finish reading the stimulus.
Kicking the idea of “a belief” as the subject up into the domain, we get to talk about the properties of beliefs. And it's those properties that have a sufficiency necessity relationship. The sufficient property is “based on reliable information.” If that's true, then the necessary property is “reasonableness.”
The next claim is an intersection claim. We know this from the presence of the word “some.” Some beliefs are based on information from a reliable source and yet are neither self-evident nor grounded in observable evidence. This is where you might notice that the subject once again is belief. The sentence here is talking about a triple intersection between three different sets of properties of beliefs.
- based on reliable information (same set as the sufficient condition in the previous sentence)
- not self-evident
- not grounded in observable evidence
These three sets have an intersection. But we also know from the first sentence that if based on reliable information, then reasonable. That implies “reasonable” gets to join this intersection with “not self-evident” and “not grounded in observable evidence” as well.
Using logic, first, represent the intersection of 2 and 3 as simply A. B will represent based on reliable information. C will represent reasonable. The triple intersection can now be represented as A ←s→ B. The conditional is B → C. The valid inference is A ←s→ C. Again, that’s just the triple intersection between “reasonable” and 2 and 3.
If that was confusing, consider this. If a cat is mild-mannered, then it’s domestic. Some mild-mannered cats are large and fluffy. Therefore, some domestic cats are large and fluffy. That’s analogous to the question here. Kick the subject “cats” up into the domain. The “some” premise describes a triple intersection between mild-mannered, large, and fluffy. Because mild-mannered implies domestic, we know that domestic also intersects with large and fluffy.
Hopefully that clears up the logic. Translating it back into English reveals that we have many options. “Some domestic cats are large and fluffy” is probably the most straightforward translation. But we could also say, “Among the large cats, some domestic ones are fluffy.” Or we could say, “Among the fluffy cats, some large ones are domestic.” The order of the modifiers in “some” intersections doesn’t matter. “Some” can be reversibly read.
So, there are many ways to translate the valid inference from the actual stimulus back into English. We could say, “Some beliefs that are neither self-evident nor grounded in observable evidence are nonetheless reasonable.” Or we could state this as Correct Answer Choice (E) does. Among reasonable beliefs that are not self-evident, there are some beliefs that are not grounded in observable evidence. Or even differently still. Grammar is the reason for this flexibility. As long as you know that you're just trying to express a triple intersection, you should be all set.
Answer Choice (A) says beliefs for which a person does not have observable evidence are unreasonable. This is a mishmash of the concepts in the stimulus. What must be true is that some beliefs for which a person does not have observable evidence are reasonable. Or alternatively, we could say that unreasonable beliefs must not be based on unreliable information.
Answer Choice (B) says beliefs based on information from a reliable source are self-evident. This is also a mishmash of the concepts above. We have no information to make claims about self-evident beliefs.
Answer Choice (C) says all reasonable beliefs for which a person has no observable evidence are based on information from a reliable source. This does not validly follow from the premises. But if we changed the quantifier “all” into the quantifier “some,” then it would follow validly.
Answer Choice (D) says if the belief is not grounded in observable evidence then it is not self-evident either. This also does not follow. The relationship between these two concepts is only one of intersection. We don't know if the two sets have a superset-subset relationship.
This is a Must Be True question.
This question tests your ability to manipulate grammar to reveal underlying logical relationships between sets. In particular, we are dealing with sets of intersections and supersets and subsets.
The stimulus states that if a belief is based on information from a reliable source, then it is reasonable to maintain that belief. This is a standard conditional claim using the “if... then...” formulation. Let's kick the idea of “a belief” up into the domain. This will simplify the analysis. You wouldn't know at this moment to do this. You have to finish reading the stimulus.
Kicking the idea of “a belief” as the subject up into the domain, we get to talk about the properties of beliefs. And it's those properties that have a sufficiency necessity relationship. The sufficient property is “based on reliable information.” If that's true, then the necessary property is “reasonableness.”
The next claim is an intersection claim. We know this from the presence of the word “some.” Some beliefs are based on information from a reliable source and yet are neither self-evident nor grounded in observable evidence. This is where you might notice that the subject once again is belief. The sentence here is talking about a triple intersection between three different sets of properties of beliefs.
- based on reliable information (same set as the sufficient condition in the previous sentence)
- not self-evident
- not grounded in observable evidence
These three sets have an intersection. But we also know from the first sentence that if based on reliable information, then reasonable. That implies “reasonable” gets to join this intersection with “not self-evident” and “not grounded in observable evidence” as well.
Using logic, first, represent the intersection of 2 and 3 as simply A. B will represent based on reliable information. C will represent reasonable. The triple intersection can now be represented as A ←s→ B. The conditional is B → C. The valid inference is A ←s→ C. Again, that’s just the triple intersection between “reasonable” and 2 and 3.
If that was confusing, consider this. If a cat is mild-mannered, then it’s domestic. Some mild-mannered cats are large and fluffy. Therefore, some domestic cats are large and fluffy. That’s analogous to the question here. Kick the subject “cats” up into the domain. The “some” premise describes a triple intersection between mild-mannered, large, and fluffy. Because mild-mannered implies domestic, we know that domestic also intersects with large and fluffy.
Hopefully that clears up the logic. Translating it back into English reveals that we have many options. “Some domestic cats are large and fluffy” is probably the most straightforward translation. But we could also say, “Among the large cats, some domestic ones are fluffy.” Or we could say, “Among the fluffy cats, some large ones are domestic.” The order of the modifiers in “some” intersections doesn’t matter. “Some” can be reversibly read.
So, there are many ways to translate the valid inference from the actual stimulus back into English. We could say, “Some beliefs that are neither self-evident nor grounded in observable evidence are nonetheless reasonable.” Or we could state this as Correct Answer Choice (E) does. Among reasonable beliefs that are not self-evident, there are some beliefs that are not grounded in observable evidence. Or even differently still. Grammar is the reason for this flexibility. As long as you know that you're just trying to express a triple intersection, you should be all set.
Answer Choice (A) says beliefs for which a person does not have observable evidence are unreasonable. This is a mishmash of the concepts in the stimulus. What must be true is that some beliefs for which a person does not have observable evidence are reasonable. Or alternatively, we could say that unreasonable beliefs must not be based on unreliable information.
Answer Choice (B) says beliefs based on information from a reliable source are self-evident. This is also a mishmash of the concepts above. We have no information to make claims about self-evident beliefs.
Answer Choice (C) says all reasonable beliefs for which a person has no observable evidence are based on information from a reliable source. This does not validly follow from the premises. But if we changed the quantifier “all” into the quantifier “some,” then it would follow validly.
Answer Choice (D) says if the belief is not grounded in observable evidence then it is not self-evident either. This also does not follow. The relationship between these two concepts is only one of intersection. We don't know if the two sets have a superset-subset relationship.
This is a Strengthen question.
The argument uses causation logic. The stimulus begins and ends with two parts of a hypothesis (a causal conclusion): first, that large trucks are not causally responsible, and second, that studded snow tires are causally responsible for ruts in the transportation official’s city.
Why should we believe this? The premises state that out of the many places that have roughly as much large truck traffic as the official’s city does and also a comparable amount of snowfall, only the few places that allow snow tires have ruts in them. This looks like the results of a controlled experiment. All else held equal, we toggle only snow tires. With snow tires, ruts. Without snow tires, no ruts.
What clearly follows from the premises is that snow tires are causally necessary since without them there are no ruts. What also follows is that large trucks are not causally sufficient since there are cities with large trucks but no ruts. Had the author reached either or both of those conclusions, the argument would be fine. But he reached a far less nuanced conclusion, one that shifted the causal blame entirely away from large trucks (yet we only know that large trucks are insufficient, not that they’re without any causal impact) and entirely onto studded snow tires (yet we only know that snow tires are causally necessary, not that they’re sufficient). Another way to understand why the argument is problematic is to consider the alternative hypothesis that also fits with the facts: both the snow tires and the large trucks have to act together to cause ruts.
Look again at the premises and notice that the facts so far fit with both the author’s hypothesis (snow tires only) and the alternative hypothesis (snow tires plus large trucks). That’s because large trucks were present in all the cities considered. We simply toggled on and off the presence of snow tires. With snow tires toggled on we find ruts, with snow tires toggled off we find no ruts. The only hypothesis excluded is the large truck only hypothesis, which is another way of saying that large trucks are not causally sufficient.
So how do we decide between the snow tires only and the snow tires plus large trucks hypotheses? Lucky for us, they make different predictions. In cities that have snow tires but no large trucks, the snow tires only hypothesis would predict ruts while the snow tires plus large trucks hypothesis would predict no ruts. Seeing what actually happens in those cities will help us decide between the two hypotheses.
This is exactly what Correct Answer Choice (C) does for us. It says that most of the places that allow snow tires yet don't have large truck traffic have ruts. This fact confirms the prediction of the snow tires only hypothesis and rules out the snow tires plus large trucks hypothesis.
Answer Choice (A) says large trucks are not allowed to have studded snow tires in many areas. This was close but also so very far. With a tiny tweak, (A) could also have ruled out the combination hypothesis. We just needed to say that in those areas that allow snow tires, large trucks are not allowed to have snow tires. That means the ruts observed in the stimulus in the cities that allowed snow tires definitely did not come from large trucks with snow tires, on the assumption that the large trucks were not in violation of this ordinance. It means that the ruts came from other snow-tired vehicles. That means it is the snow tires and not large trucks that are causally responsible for the ruts.
Answer Choice (B) says the number of ruts in the roads of the official's city has declined recently as the amount of large truck traffic has diminished. This correlational phenomenon is inconsistent with the causal hypothesis in the argument. If it's true that large trucks don't cause ruts then we wouldn't expect to see any difference in the number of ruts as large truck traffic either increases or decreases. Because (B) disconfirms that prediction, it weakens the argument.
Answer Choice (D) says some cities with even more truck traffic than the official's city also have ruts in their roads. This is useless because we don't know whether those cities allow snow tires.
Answer Choice (E) says most places that have little snowfall do not allow the use of snow tires. That makes sense. But it's not clear how this has anything to do with the argument. We don't know whether those places have large truck traffic nor do we know whether they have ruts in their roads.
This is a Strengthen question.
The argument uses causation logic. The stimulus begins and ends with two parts of a hypothesis (a causal conclusion): first, that large trucks are not causally responsible, and second, that studded snow tires are causally responsible for ruts in the transportation official’s city.
Why should we believe this? The premises state that out of the many places that have roughly as much large truck traffic as the official’s city does and also a comparable amount of snowfall, only the few places that allow snow tires have ruts in them. This looks like the results of a controlled experiment. All else held equal, we toggle only snow tires. With snow tires, ruts. Without snow tires, no ruts.
What clearly follows from the premises is that snow tires are causally necessary since without them there are no ruts. What also follows is that large trucks are not causally sufficient since there are cities with large trucks but no ruts. Had the author reached either or both of those conclusions, the argument would be fine. But he reached a far less nuanced conclusion, one that shifted the causal blame entirely away from large trucks (yet we only know that large trucks are insufficient, not that they’re without any causal impact) and entirely onto studded snow tires (yet we only know that snow tires are causally necessary, not that they’re sufficient). Another way to understand why the argument is problematic is to consider the alternative hypothesis that also fits with the facts: both the snow tires and the large trucks have to act together to cause ruts.
Look again at the premises and notice that the facts so far fit with both the author’s hypothesis (snow tires only) and the alternative hypothesis (snow tires plus large trucks). That’s because large trucks were present in all the cities considered. We simply toggled on and off the presence of snow tires. With snow tires toggled on we find ruts, with snow tires toggled off we find no ruts. The only hypothesis excluded is the large truck only hypothesis, which is another way of saying that large trucks are not causally sufficient.
So how do we decide between the snow tires only and the snow tires plus large trucks hypotheses? Lucky for us, they make different predictions. In cities that have snow tires but no large trucks, the snow tires only hypothesis would predict ruts while the snow tires plus large trucks hypothesis would predict no ruts. Seeing what actually happens in those cities will help us decide between the two hypotheses.
This is exactly what Correct Answer Choice (C) does for us. It says that most of the places that allow snow tires yet don't have large truck traffic have ruts. This fact confirms the prediction of the snow tires only hypothesis and rules out the snow tires plus large trucks hypothesis.
Answer Choice (A) says large trucks are not allowed to have studded snow tires in many areas. This was close but also so very far. With a tiny tweak, (A) could also have ruled out the combination hypothesis. We just needed to say that in those areas that allow snow tires, large trucks are not allowed to have snow tires. That means the ruts observed in the stimulus in the cities that allowed snow tires definitely did not come from large trucks with snow tires, on the assumption that the large trucks were not in violation of this ordinance. It means that the ruts came from other snow-tired vehicles. That means it is the snow tires and not large trucks that are causally responsible for the ruts.
Answer Choice (B) says the number of ruts in the roads of the official's city has declined recently as the amount of large truck traffic has diminished. This correlational phenomenon is inconsistent with the causal hypothesis in the argument. If it's true that large trucks don't cause ruts then we wouldn't expect to see any difference in the number of ruts as large truck traffic either increases or decreases. Because (B) disconfirms that prediction, it weakens the argument.
Answer Choice (D) says some cities with even more truck traffic than the official's city also have ruts in their roads. This is useless because we don't know whether those cities allow snow tires.
Answer Choice (E) says most places that have little snowfall do not allow the use of snow tires. That makes sense. But it's not clear how this has anything to do with the argument. We don't know whether those places have large truck traffic nor do we know whether they have ruts in their roads.
This is a Weaken question.
This argument starts with a hypothesis-conclusion. We are supposed to believe that the rise of mega-bookstores in the 90s increased sales of bestsellers but decreased sales of literary books. Why should we believe this? The remaining three sentences are the premises. First we learned that in 1986, best-selling hardcovers accounted for 7% of all hardcover sales, but by 1996, 10 years later, best-selling hardcovers accounted for 14% of all hardcover sales. If the conclusion rested solely on this premise, then the argument would be pretty weak because surely there are alternative explanations. This premise only establishes that the mega-bookstores coincided with this change in proportion of best-selling hardcovers.
And so the argument continues with another premise that attempts to explain how the mega-bookstores caused this change. It says that mega-bookstores can offer deeper discounts than independent bookstores and that they offer their biggest discounts on best-selling hardcovers, which encourages their sales at the expense of literary works.
At this point, you might be thinking about two seemingly different considerations, one about alternative hypotheses since even with the final premise being true, there still exists alternative explanations for the data. The other consideration comes from recognizing that there is a part to whole or subset to superset assumption present.
Correct Answer Choice (C) reveals that these two seemingly different considerations both arise from the same issue. Let’s start with the perhaps more obvious consideration of part to whole. You may have noticed that the premises only talk about hardcover book sales whereas the conclusion talks about all book sales. And so (C) says in the 90s, the literary works increasingly had their initial publication in paperback editions rather than hardcover editions. That means the data in the premises about hardcovers isn't the whole story. Even if it's true that mega-bookstores encouraged more best-selling hardcovers at the expense of literary hardcovers, and even if it’s true that that strategy is what accounts for the 7% doubling to 14%, we’re still only talking about hardcovers. The conclusion could still be false, meaning literary books could have been selling just fine. People were simply purchasing paperback literary works.
And this leads to the alternative hypothesis. One way of explaining the phenomenon described in the 10-year period between 1986 and 1996, that is, the doubling of best-selling hardcovers from 7% to 14%, is the account offered in the conclusion, that the rise of mega-bookstores increased sales of bestsellers at the expense of literary books. But that's not the only story you can tell. Another hypothesis to account for the increasing share of hardcover bestsellers is simply that the non-bestsellers (the literary books) stopped publishing in hardcover. If that's the case, then everything the premises offer can still be true, the statistic is still what it is, it's still true that mega-bookstores offer big discounts on best-selling hardcovers, which encourages their sales and discourages other hardcovers, but now we no longer believe that sales of literary works overall suffered, because, again, what happened in hardcover isn’t the whole story.
Answer Choice (A) says bookstore customers are more likely to purchase a book that they have seen on a bestseller list than one that they have not. (A) reveals the causal effect of being on a bestseller list. It causes people to buy the book. But it's not clear how this is relevant to the argument. Surely the argument already assumed this. In fact, what would a “bestseller” be if not a book that appeared on bestsellers' lists?
Answer Choice (B) says in the 90s, bookstore customers' most frequent purchases were books written by authors who had already written at least one bestseller. Like (A), it's not clear how this is relevant. The argument never assumed that bookstore customers' most frequent purchases were by obscure authors. So pointing out that they weren’t doesn’t harm the argument.
Answer Choice (D) says by 1996 there were about 20% more titles in print than in 1986. So in other words, in the 10 years that passed, if we imagine the number of titles in print to represent an entire pie, then the whole pie got 20% bigger. But the premise already reported data as a proportion, that is to say, as a slice. In 1986, bestsellers accounted for a 7% slice of the whole pie. 10 years later, bestsellers accounted for 14% of the whole but larger pie. So, if 10 years ago, I gave you a 7% slice of a pizza pie and then 10 years later, I gave you a 14% slice of another same-sized pizza pie, then you’d have exactly twice as much pie. But if the second pizza pie was larger than the first, then you’re getting more than twice as much pie.
So, as much fun as it might be to think about getting more pizza, it doesn’t have any bearing on the argument. How is this supposed to affect the reasoning? And by the way, (D) talks about overall titles in print whereas the stimulus reported only statistics from hardcover titles, which is merely a subset of the total titles. In other words, the stimulus only talked about a subset of the whole pie.
Answer Choice (E) says books that are not expected to be bestsellers are featured more often in independent bookstores than in mega-bookstores. What are we supposed to do with this information? If anything, this information is consistent with the argument. The author already told us that mega-bookstores can offer deep discounts on bestsellers which encourage their sales at the expense of literary books.
A
Bookstore customers are more likely to purchase a book that they have seen on a best-seller list than one that they have not.
B
In the 1990s, bookstore customers’ most frequent purchases were books written by authors who had already written at least one best-seller.
C
In the 1990s, less commercial, more literary works increasingly had their initial publication in paperback editions rather than hardback editions.
D
By 1996, there were about 20 percent more titles in print than in 1986.
E
Books that are not expected to be best-sellers are featured more often in independent bookstores than in book megastores.
This is a Weaken Except question, so that means four answers cut against assumptions that the argument made.
Usually when you see a Weaken Except question, that means the argument is especially bad because how else can there be so many assumptions for the answers to contradict? This argument is no exception. It really is bad. And it's bad for having made two different types of assumptions. This can be difficult to recognize. Another difficulty is the use of jargon and the reference to ratios. If it's one thing that LSAT students don't like, it's scientific jargon and math. Both are present here.
The first sentence states a causal relationship that occurs on Earth. On Earth, biological activity leads to, i.e., causes, a change in the ratio. So this is my advice about how to overcome the hurdle of jargon and also incidentally the hurdle of “math.” They don't matter. They don't matter because the rest of the argument and all the answer choices consistently reference the same “ratio.” So who cares what the ratio is called? All we need to focus on is the causal relationship, which is that biological activity causes a change in the ratio.
The next sentence tells us that a newly discovered meteorite, a rock, from Mars exhibits ratios found only in terrestrial minerals dating from before the beginning of life on Earth. The sentence takes a bit of parsing to understand. First, you have to understand that terrestrial minerals mean rocks on Earth. So, in other words, the ratio we find in this rock from Mars is similar to the ratio we find in rocks from Earth before there was life on Earth.
Now we get to the conclusion. The author concludes that it's unlikely life occurred on Mars.
I already said there are two different types of assumptions here. One is the assumption of analogy. This argument relies on reasoning by analogy because it assumes that the causal relationship on Earth of biological activity causing a change in the ratio would also be present on Mars. Would it? Mars and Earth are different places and those differences could mean that this causal relationship isn’t analogous. This is what Answer Choice (A) and Answer Choice (B) point out.
Answer Choice (B) says the effects of life on the ratio depend on a number of climatic and environmental factors with regard to which Earth and Mars differ. This is a very straightforward way of disanalogizing Earth and Mars. (B) tells us that biological activity isn't the only cause that's involved in the alteration of the ratio. Other causes matter too, like climatic and environmental factors, and those factors are different between Mars and Earth. So the ratio found in the Mars rock may not indicate the absence of life on Mars after all.
Answer Choice (A) is more subtle than (B) but also works on the argument’s reasoning by analogy. It says life forms that have a different effect on the ratio from that of life forms on Earth could have evolved elsewhere. This means that we shouldn't assume that Earth life forms’ effects on the ratio is universal. That means it's possible that different kinds of life forms could have evolved elsewhere and that those extraterrestrial life forms could have had a different effect on the ratio. This is an indirect way of suggesting that Mars and Earth are disanalogous. (A) is suggesting that if life had evolved on Mars, it's possible that Martian life would have had a different effect on the ratio.
Of the four answers that weaken the argument, these are the two that cut against the argument’s use of reasoning by analogy. They point out dissimilarities between Earth and Mars. (B) does this specifically and explicitly. (A) does this indirectly by suggesting that Earth and other places in general may be crucially dissimilar.
The other two answers that weaken the argument do so by cutting against a different assumption. That’s the assumption that the single Martian rock tells us something about the state of the Martian planet. If you think about it, it might occur to you that Mars is a big place and the meteorite is quite small by comparison. Is it true that the properties of that single rock reveal something about the entire planet? Well, that all depends on what properties of the rock we’re talking about and what characteristics of the planet we’re trying to figure out. In some ways, surely this rock is representative of Mars. But don't assume that it is representative of Mars in all ways. This is what Answer Choice (D) and Answer Choice (E) point out.
Answer Choice (E) says the current ratio on Mars is different from that at the time the meteorite left Mars. That means the ratio in the rock is not representative of the ratio on Mars today. That means this rock is not evidence of what has happened on Mars since it left the planet. Has life evolved in the intervening time? It’s unclear. (E) severely undermines the relevance of the only piece of evidence on which the conclusion is based by declaring the evidence to be chronologically unrepresentative.
Answer Choice (D) says that relatively few terrestrial mineral samples (rocks we find on Earth) contain ratios that would indicate the presence of life. This is a subtler way of calling out the representativeness of the rock from Mars. (D) says that if we looked at the ratios of rocks on Earth, we would find no signs of biological activity. Yet we know there is obviously plenty of biological activity on Earth. Therefore, this method of reasoning, that is, using the ratio found in rocks, is a poor way of figuring out whether there is life on Earth. This suggests that using this kind of reasoning might also lead to a faulty conclusion for Mars. I'm careful to say “suggests” because I recognize that this (meta) argument itself depends on an analogy between Mars and Earth. The crucial similarity assumed is that just like on Earth, even if there was biological activity on Mars, most of the rocks on Mars would not reflect that activity. That means there’s a good chance that this sample, this only piece of evidence we have, would also fail to capture the effects of life on Mars.
As you can see from the way these answers are structured, (B) and (E) are the more explicit refutations of the two assumptions in the argument. (A) and (D) are the subtler counterparts. They merely suggest that the assumptions are questionable.
Correct Answer Choice (C) says the ratio in the rock from Mars is the same as that on the planet as a whole at the time that the rock left Mars. This doesn't hurt the argument. This helps the argument, though only a little. Now we can be sure that this rock was representative of the ratio on Mars as a whole at some point in time. It doesn't guarantee that it's still representative of the ratio on the planet in the intervening time, as (E) points out, but it does at least partially patch up the issue of representativeness.
This is a Weaken Except question, so that means four answers cut against assumptions that the argument made.
Usually when you see a Weaken Except question, that means the argument is especially bad because how else can there be so many assumptions for the answers to contradict? This argument is no exception. It really is bad. And it's bad for having made two different types of assumptions. This can be difficult to recognize. Another difficulty is the use of jargon and the reference to ratios. If it's one thing that LSAT students don't like, it's scientific jargon and math. Both are present here.
The first sentence states a causal relationship that occurs on Earth. On Earth, biological activity leads to, i.e., causes, a change in the ratio. So this is my advice about how to overcome the hurdle of jargon and also incidentally the hurdle of “math.” They don't matter. They don't matter because the rest of the argument and all the answer choices consistently reference the same “ratio.” So who cares what the ratio is called? All we need to focus on is the causal relationship, which is that biological activity causes a change in the ratio.
The next sentence tells us that a newly discovered meteorite, a rock, from Mars exhibits ratios found only in terrestrial minerals dating from before the beginning of life on Earth. The sentence takes a bit of parsing to understand. First, you have to understand that terrestrial minerals mean rocks on Earth. So, in other words, the ratio we find in this rock from Mars is similar to the ratio we find in rocks from Earth before there was life on Earth.
Now we get to the conclusion. The author concludes that it's unlikely life occurred on Mars.
I already said there are two different types of assumptions here. One is the assumption of analogy. This argument relies on reasoning by analogy because it assumes that the causal relationship on Earth of biological activity causing a change in the ratio would also be present on Mars. Would it? Mars and Earth are different places and those differences could mean that this causal relationship isn’t analogous. This is what Answer Choice (A) and Answer Choice (B) point out.
Answer Choice (B) says the effects of life on the ratio depend on a number of climatic and environmental factors with regard to which Earth and Mars differ. This is a very straightforward way of disanalogizing Earth and Mars. (B) tells us that biological activity isn't the only cause that's involved in the alteration of the ratio. Other causes matter too, like climatic and environmental factors, and those factors are different between Mars and Earth. So the ratio found in the Mars rock may not indicate the absence of life on Mars after all.
Answer Choice (A) is more subtle than (B) but also works on the argument’s reasoning by analogy. It says life forms that have a different effect on the ratio from that of life forms on Earth could have evolved elsewhere. This means that we shouldn't assume that Earth life forms’ effects on the ratio is universal. That means it's possible that different kinds of life forms could have evolved elsewhere and that those extraterrestrial life forms could have had a different effect on the ratio. This is an indirect way of suggesting that Mars and Earth are disanalogous. (A) is suggesting that if life had evolved on Mars, it's possible that Martian life would have had a different effect on the ratio.
Of the four answers that weaken the argument, these are the two that cut against the argument’s use of reasoning by analogy. They point out dissimilarities between Earth and Mars. (B) does this specifically and explicitly. (A) does this indirectly by suggesting that Earth and other places in general may be crucially dissimilar.
The other two answers that weaken the argument do so by cutting against a different assumption. That’s the assumption that the single Martian rock tells us something about the state of the Martian planet. If you think about it, it might occur to you that Mars is a big place and the meteorite is quite small by comparison. Is it true that the properties of that single rock reveal something about the entire planet? Well, that all depends on what properties of the rock we’re talking about and what characteristics of the planet we’re trying to figure out. In some ways, surely this rock is representative of Mars. But don't assume that it is representative of Mars in all ways. This is what Answer Choice (D) and Answer Choice (E) point out.
Answer Choice (E) says the current ratio on Mars is different from that at the time the meteorite left Mars. That means the ratio in the rock is not representative of the ratio on Mars today. That means this rock is not evidence of what has happened on Mars since it left the planet. Has life evolved in the intervening time? It’s unclear. (E) severely undermines the relevance of the only piece of evidence on which the conclusion is based by declaring the evidence to be chronologically unrepresentative.
Answer Choice (D) says that relatively few terrestrial mineral samples (rocks we find on Earth) contain ratios that would indicate the presence of life. This is a subtler way of calling out the representativeness of the rock from Mars. (D) says that if we looked at the ratios of rocks on Earth, we would find no signs of biological activity. Yet we know there is obviously plenty of biological activity on Earth. Therefore, this method of reasoning, that is, using the ratio found in rocks, is a poor way of figuring out whether there is life on Earth. This suggests that using this kind of reasoning might also lead to a faulty conclusion for Mars. I'm careful to say “suggests” because I recognize that this (meta) argument itself depends on an analogy between Mars and Earth. The crucial similarity assumed is that just like on Earth, even if there was biological activity on Mars, most of the rocks on Mars would not reflect that activity. That means there’s a good chance that this sample, this only piece of evidence we have, would also fail to capture the effects of life on Mars.
As you can see from the way these answers are structured, (B) and (E) are the more explicit refutations of the two assumptions in the argument. (A) and (D) are the subtler counterparts. They merely suggest that the assumptions are questionable.
Correct Answer Choice (C) says the ratio in the rock from Mars is the same as that on the planet as a whole at the time that the rock left Mars. This doesn't hurt the argument. This helps the argument, though only a little. Now we can be sure that this rock was representative of the ratio on Mars as a whole at some point in time. It doesn't guarantee that it's still representative of the ratio on the planet in the intervening time, as (E) points out, but it does at least partially patch up the issue of representativeness.
A
Life forms that have a different effect on the ratio of S-34 to S-32 from that of life forms on Earth could have evolved elsewhere.
B
The effects of life on the ratio of S-34 to S-32 depend on a number of climatic and environmental factors with regard to which Earth and Mars differ.
C
The ratio of S-34 to S-32 in the meteorite is the same as that on Mars as a whole at the time that the material in the meteorite left Mars.
D
Relatively few terrestrial mineral samples contain S-34 and S-32 in the ratio that indicates the presence of biological activity.
E
The current ratio of S-34 to S-32 on Mars is different from that at the time the material in the meteorite left Mars.
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.