A new screening test has been developed for syndrome Q. Research has shown that the test yields a positive for syndrome Q whenever the person tested has that syndrome. So, since Justine shows positive on the test, she must have syndrome Q.

Summarize Argument
The author concludes that Justine has syndrome Q. He supports this by saying that if someone has syndrome Q, they test positive, and Justine tested positive.

Identify and Describe Flaw
This is the cookie-cutter flaw of confusing necessary and sufficient conditions. The author treats “positive” as sufficient for “syndrome Q,” but according to his premises, “positive” is necessary.
In other words, just because Justine tested positive doesn’t necessarily mean that she has syndrome Q. She might just have had a false positive test.

A
It confuses the claim that a subject will test positive when the syndrome is present with the claim that any subject who tests positive has the syndrome.
The author treats testing positive as sufficient for having syndrome Q. But his premises say that it’s necessary: if someone does have syndrome Q, then they will test positive, not the other way around. So Justine might not have syndrome Q, even though she tested positive.
B
It makes a general claim regarding the accuracy of the test for syndrome Q without providing adequate scientific justification for that claim.
The author claims that the test is accurate and positive when someone does have syndrome Q. He doesn’t necessarily need to provide scientific justification for this, but he does say that research has proven it to be true.
C
It fails to adequately distinguish between a person’s not having syndrome Q and that person’s not testing positive for syndrome Q.
Instead, the author fails to distinguish between a person testing positive for syndrome Q and that person having syndrome Q. He doesn’t mistake a person not having syndrome Q with that person not testing positive for it.
D
It confuses a claim about the accuracy of a test for syndrome Q in an arbitrary group of individuals with a similar claim about the accuracy of the test for a single individual.
The author never confuses his claim about the test’s overall accuracy with his claim about Justine’s test. Also, we have no reason to believe that the research used an “arbitrary group” when measuring the test’s accuracy.
E
It confuses the test’s having no reliable results for the presence of syndrome Q with its having no reliable results for the absence of syndrome Q.
If someone does have syndrome Q, then they test positive. So the test does have reliable results for the presence of syndrome Q. We don’t know whether it has reliable results for the absence of syndrome Q, but regardless, the author never confuses the ideas presented in (E).

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The level of triglycerides in the blood rises when triglycerides are inadequately metabolized. Research shows that patients with blood triglyceride levels above 1 milligram per milliliter are twice as prone to heart attacks as others. Thus, it is likely that consuming large amounts of fat, processed sugar, or alcohol, each known to increase triglyceride levels in the blood, is a factor causing heart disease.

Summarize Argument: Phenomenon-Hypothesis
The author concludes that eating lots of fat, processed sugar, or alcohol, can contribute to heart disease. This is based on the fact that these things increase blood triglyceride levels, and the hypothesis that higher blood triglyceride increases the risk of heart disease. This hypothesis is based on research that shows a correlation between blood triglyceride levels above 1 milligram per millileter and higher likelihood of heart attacks.

Notable Assumptions
The author assumes that there’s no other explanation for the correlation observed betwen blood triglyceride levels and heart attacks. The author also assumes that there aren’t other things in fat, processed sugar, and alcohol that tend to decrease the risk of heart attacks.

A
People with a high-fat diet who engage in regular, vigorous physical activity are much less likely to develop heart disease than are sedentary people with a low-fat diet.
This suggests physical activity is also a causal factor in heart disease. But this doesn’t suggest high fat consumption isn’t also a causal factor. (A) could have been correct if we knew that people with high blood triglyceride on average exercise a less than others.
B
Triglyceride levels above 2 milligrams per milliliter increase the risk of some serious illnesses not related to heart disease.
Other diseases aren’t relevant to whether triglyceride levels are a causal factor in heart disease.
C
Shortly after a person ceases to regularly consume alcohol and processed sugar, that person’s triglyceride levels drop dramatically.
This strengthens the connection between consumption of alcohol/sugar and triglyceride. This is consistent with the author’s reasoning.
D
Heart disease interferes with the body’s ability to metabolize triglycerides.
This suggests an alternate explanation for the correlation between higher blood triglyceride levels and heart attacks. If heart disease interferes with triglyceride metabolization, it would lead to higher blood triglyceride. This suggests the cause and effect could be reversed.
E
People who maintain strict regimens for their health tend to adopt low-fat diets and to avoid alcohol and processed sugar.
This has no impact, because we don’t know whether the people on these low-fat and low-sugar diets are more or less likely than others to have heart attacks.

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Some food historians conclude that recipes compiled by an ancient Roman named Apicius are a reliable indicator of how wealthy Romans prepared and spiced their food. Since few other recipes from ancient Rome have survived, this conclusion is far too hasty. After all, the recipes of Apicius may have been highly atypical, just like the recipes of many notable modern chefs.

Summarize Argument: Counter-Position
Some historians conclude that recipes compiled by Apicius are a reliable indicator of how wealthy Romans made their food. The author’s conclusion is that the historian’s conclusion isn’t necessarily true. This is because only a few other recipes from Apicius’s time have survived, and Apicius’s recipes may be unrepresentative of ancient Roman food. The author also relies on an analogy to many modern chefs; just as their recipes are unusual, so too might be Apicius’s.

Describe Method of Reasoning
The author criticizes the historian’s conclusion by pointing out that it might be based on an unrepresentative sample of recipes. The author also relies on an analogy to support the possibility that the sample is unrepresentative.

A
It rejects a view held by some food historians solely on the grounds that there is insufficient evidence to support it.
Calling a conclusion “too hasty” is not the same as rejecting it. The author doesn’t necessarily believe the historians are wrong; he’s simply pointing out they might be wrong. Also, the author relies on an analogy; not “solely” on the claim that there’s insufficient evidence.
B
It offers support for a view held by some food historians by providing a modern analogue to that view.
The author does not support the historians’ view. He points out that there are reasons to think it might not be true.
C
It takes issue with the view of some food historians by providing a modern analogue that purportedly undercuts their view.
The author takes issue with the view of the historians (”the conclusion is too hasty”) by providing a modern analogue (”many notable modern chefs”) that purportedly undercuts the historians’ view (suggesting that Apicius’s recipes might be unrepresentative).
D
It uses a conclusion drawn by some food historians as the basis for a conclusion about a modern analogue.
The author’s conclusion is not about the modern chefs. The modern chefs are used as support for the conclusion that the historian’s conclusion is too hasty.
E
It tries to bolster a conclusion about the similarity of historical times to modern times by comparing a conclusion drawn by some food historians to a modern analogue.
The conclusion is not about the “similarity of historical times to modern times.” The author uses an analogy to modern chefs to conclude that we do not necessarily know that Apicius’s recipes are representative of the food of wealthy ancient Romans.

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Music historian: In the past, radio stations would not play rock songs that were more than three minutes in length. Rock musicians claimed that such commercial barriers limited their creativity, and some critics argue that only since those barriers have been lifted has rock music become artistic. In fact, however, when these barriers were lifted, the standards for song structures broke down and the music became aimless, because the styles from which rock derived were not well suited to songs of extended length.

Summary

Usually, radio stations do not play rock songs longer than three minutes. Rock musicians argue that this time constraint limited their creativity, and some critics argue that rock music has become artistic only because this time constraints have been lifted. However, song structures began to break down and music became aimless when the time constraints were lifted. This is because the styles that are the basis of rock music are not well suited for songs of extended length.

Strongly Supported Conclusions

In some cases, rock music can benefit from time constraints rather than be harmed by them.

A
Rock music is not a good outlet for creative musicians who have a great many ideas.

This answer is unsupported. To say that rock music is not a good outlet for creativity is too extreme. We only know rock musicians argue that time constraints limit creativity, not eliminate creativity entirely.

B
Rock music must borrow from styles more conducive to songs of extended length if it is to become artistic.

This answer is unsupported. To say that rock music must borrow from other styles is too extreme. We don’t know from the stimulus if there are any styles that are suited for songs of extended length.

C
Rock music requires more discipline than some other forms of music.

This answer is unsupported. We are not told anything about other forms of music in order to make this comparison.

D
Rock music can sometimes benefit from the existence of commercial barriers rather than being harmed by them.

This answer is strongly supported. We know from the stimulus that, after time constraints were lifted, song structures began to break down. Therefore, rock music benefited at least somewhat from the time constraints.

E
Rock music is best when it is made by musicians who do not think of themselves as being self-conscious artists.

This answer is unsupported. We don’t know from the stimulus under what circumstances rock music is the best.


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A recently discovered fossil, which is believed by some to come from Archaeoraptor liaoningensis, a species of dinosaur, can serve as evidence that birds evolved from dinosaurs only if the entire fossil is from a single animal. However, the fossil is a composite of bones collected from various parts of the discovery site, so it does not provide evidence that birds evolved from dinosaurs.

Summary
The author concludes that a recently discovered fossil does not provide evidence that birds evolved from dinosaurs. Why? Because of the following:
In order for a fossil to serve as evidence that birds evolved from dinosaurs, it must be the case that the entire fossil is from a single animal.
But the recently discovered fossil is a compositive of bones collected from different parts of the discovery site.

Missing Connection
We know from the first premise that if the fossil isn’t from a single animal, then it isn’t evidence that birds evolved from dinosaurs. But do we have enough to establish that the fossil isn’t from a single animal? No — all we know from the other premise is that the fossil is a composite of bones from different parts of the discovery site. But couldn’t the bones still be from the same animal?
To make the argument valid, then, we want to prove that the fossil is not from the same animal. We can do this by establishing that if the fossil is a composite from different areas of the discovery site, it must come from more than one animal.

A
The only paleontologists who believe that the entire fossil is from a single animal are those who were already convinced that birds evolved from dinosaurs.
(A) doesn’t establish that the fossil comes from multiple animals. What scientists believe about the fossil doesn’t establish that it comes from multiple animals.
B
If the fossil is a composite, then it has pieces of more than one animal.
We know from a premise that the fossil is a composite. According to (B), then, it has pieces of more than one animal. Since the fossil isn’t just from a single animal, we can conclude that the fossil cannot serve as evidence that birds evolved from dinosaurs.
C
There are other fossils that provide evidence that birds evolved from dinosaurs.
(C) doesn’t establish that the fossil comes from multiple animals. What is true about other fossils doesn’t prove the origin of this fossil.
D
If the entire fossil is from a single animal, then it is a well-preserved specimen.
We don’t know that the fossil is NOT a well-preserved specimen. So (D) doesn’t establish that the fossil comes from multiple animals.
E
The fossil was stolen from the discovery site and sold by someone who cared much more about personal profit than about the accuracy of the fossil record.
(E) doesn’t establish that the fossil comes from multiple animals.

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Until recently it was widely believed that only a limited number of species could reproduce through parthenogenesis, reproduction by a female alone. But lately, as interest in the topic has increased, parthenogenesis has been found in a variety of unexpected cases, including sharks and Komodo dragons. So the number of species that can reproduce through parthenogenesis must be increasing.

Summarize Argument

The author concludes that the number of species that can reproduce through parthenogenesis must be increasing. She supports this by noting that, as interest in the topic has grown, parthenogenesis has been discovered in more unexpected species.

Identify and Describe Flaw

The author assumes that parthenogenesis is on the rise just because more cases have been discovered. She overlooks the possibility that these species may have always reproduced this way, and humans are just now aware of it. In other words, the lack of interest and knowledge about parthenogenesis in the past doesn't mean that it didn't occur before.

A
equates mere interest in a subject with real understanding of that subject

The author never assumes that people’s increased interest in parthenogenesis means that they really understand it. She just claims that more cases of parthenogenesis have been found since interest in it has increased.

B
takes for granted that because one thing follows another, the one must have been caused by the other

This is the cookie-cutter flaw of assuming that correlation proves causation. The author doesn’t draw a causal conclusion at all. She concludes that the number of species that use parthenogenesis is increasing, but she doesn’t say that increased interest caused this increase.

C
takes ignorance of the occurrence of something as conclusive evidence that it did not occur

The author assumes that humans’ ignorance of certain species’ ability to reproduce through parthenogenesis is evidence that they could not reproduce this way before. But it’s more likely that these species always reproduced this way, and humans are just now aware of it.

D
overlooks a crucial difference between two situations that the argument presents as being similar

This is describing a flawed analogy. The author doesn’t make this mistake. She doesn’t present two situations as being similar in the first place. Instead, she assumes that parthenogenesis is on the rise just because more cases have been discovered.

E
presumes that because research is new it is, on that basis alone, better than older research

The author never assumes that new research is better than old research. She points out that humans are aware of more cases of parthenogenesis than they were in the past. But her flaw is in the assumption that this increased knowledge means that parthenogenesis is on the rise.


15 comments

Winds, the movement of gases in the atmosphere of a planet, are ultimately due to differences in atmospheric temperature. Winds on Earth are the result of heat from the Sun, but the Sun is much too far away from Jupiter to have any significant impact on the temperature of Jupiter’s atmosphere. Nevertheless, on Jupiter winds reach speeds many times those of winds found on Earth.

"Surprising" Phenomenon
Winds on Earth are the result of heat from the Sun, yet winds on Jupiter are significantly stronger despite not being caused by the Sun.

Objective
The right answer will be a hypothesis that explains how winds on Jupiter are generated, and why those are stronger than winds on Earth. The hypothesis must show that winds can be caused by something other than the Sun’s heat.

A
Unlike Earth, Jupiter’s atmosphere is warmed by the planet’s internal heat source.
Rather than the Sun’s heat, Jupiter’s wind is caused by the planet’s internal heat source. This internal heat source could certainly have a stronger effect on Jupiter’s atmosphere than the Sun does on Earth’s atmosphere. Thus, Jupiter has stronger winds than Earth.
B
Jupiter’s atmosphere is composed of several gases that are found in Earth’s atmosphere only in trace amounts.
We don’t know enough about these gases for this to explain the surprise in the stimulus. We need to know how these gases are moved around by difference in atmospheric pressure, which on Earth is caused by the Sun.
C
Gaseous planets such as Jupiter sometimes have stronger winds than do rocky planets such as Earth.
We already know Jupiter has stronger winds than Earth does. We need to know how that’s possible, given that the Sun can’t cause winds on Jupiter like it does on Earth.
D
There are more planets that have winds stronger than Earth’s than there are planets that have winds weaker than Earth’s.
This doesn’t tell us how Jupiter’s winds are generated. It doesn’t matter how many planets in the universe have stronger winds than Earth.
E
Planets even farther from the Sun than Jupiter are known to have atmospheric winds.
This doesn’t explain how winds are generated on Jupiter or planets further from the Sun, which is what we need to explain the surprise in the stimulus.

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