Quincy: I am skeptical that the association between the lights and the earthquakes is anything more than a coincidence. The theory that ground stresses related to earthquakes can cause any kind of lightning is extremely speculative.
Summarize Argument: Counter-Position
Quincy concludes that Phoebe’s explanation of strange glowing lights as earthquake-induced is unconvincing. This is supported by the claim that the mechanism Phoebe proposes for her explanation—ball lightning forming as a result of ground stresses—is “extremely speculative.”
Describe Method of Reasoning
Quincy counters Phoebe’s argument by casting doubt on the mechanism she proposes to explain a phenomenon. By pointing out that earthquake-related ground stresses are not known to cause any kind of lightning, Quincy undermines Phoebe’s conclusion that the strange lights were “almost certainly” caused by earthquakes.
A
takes a correlation to be a causal relation
Quincy doesn’t say that any causal relationship exists based on a correlation. In fact, he’s arguing against Phoebe’s claim that a causal relationship exists.
B
challenges the accuracy of the data about sightings that Phoebe takes for granted
Quincy doesn’t challenge the accuracy of any of Phoebe’s data about the sightings. He accepts that the sightings have happened; he only doubts her explanation for the phenomenon.
C
criticizes Phoebe’s explanation as unsubstantiated
Quincy criticizes Phoebe’s explanation of strange glowing lights being ball lightning caused by earthquakes, because it is founded on a speculative—meaning unsubstantiated—theory about the potential of earthquakes to cause lightning.
D
offers an explanation of the glowing lights different from Phoebe’s
Quincy doesn’t offer any alternative explanation of the glowing lights, only casts doubt on the plausibility of Phoebe’s explanation.
E
accuses Phoebe of introducing irrelevant information
Quincy doesn’t claim that Phoebe has introduce any irrelevant information, only that she has interpreted the information in a questionable way based on speculative theories.
Summary
The stimulus can be diagrammed as follows:
Notable Valid Inferences
Most speed readers have above-average intelligence.
A
Some people can speed-read, and are able to fully concentrate, but are of below-average intelligence.
This must be false. We know that all people who are able to fully concentrate are of above-average intelligence.
B
All people who can speed-read are of above-average intelligence.
This could be true. We know for sure that most speed readers are of above-average intelligence; it could still be true that all are of above average intelligence.
C
Many people of above-average intelligence are unable to fully concentrate.
This could be true. We know that all people who can fully concentrate are of above-average intelligence, but this doesn’t mean that everyone of above-average intelligence can fully concentrate.
D
Some people with little ability to concentrate are of below-average intelligence, but can speed-read.
This could be true. If someone of is below-average intelligence, then they can’t fully concentrate. It could totally be the case that this person has the ability to speed read.
E
All people who can speed-read are able to concentrate to some extent.
This could be true. The only factor related to concentration discussed in the stimulus is “full concentration;” it could be the case that all people who can speed read can concentrate at least a little bit.
A
a nation that fails to invest in its infrastructure need not experience any resulting decline in its standard of living
The author’s conclusion is about a nation experiencing a rise in its standard of living as a result of investment in its infrastructure, not a decline in standard of living as a result of failing to invest in infrastructure.
B
many nations are unable to make the needed investments in infrastructure
Like (C) and (E) this may be true, but it doesn’t impact the author’s argument. Even if many nations can’t invest in infrastructure, it doesn’t affect the conclusion that such investments are necessary for a higher standard of living.
C
the rise in a nation’s standard of living that is prompted by investment in its infrastructure may take a long time to occur
Like (B) and (E) this may be true, but it doesn’t impact the argument. Even if the rise in standard of living takes a long time, it doesn’t affect the conclusion that investments in infrastructure are necessary for it to occur. The author even notes that it happens “over time.”
D
a rise in a nation’s standard of living need not be the result of major investments in its infrastructure
The author mistakenly assumes that investments in infrastructure are necessary, rather than merely sufficient, for a nation to experience a rise in its standard of living. But a nation’s standard of living could improve for other reasons, without investments in infrastructure.
E
nations often experience short-term crises that require that resources be diverted to purposes other than the maintenance and improvement of infrastructure
Like (B) and (C) this may be true, but it doesn’t impact the argument. Even if a nation can’t invest in infrastructure, it doesn’t affect the conclusion that such investments are necessary for a higher standard of living.
Campisi: I find your inference unconvincing; several leavens other than yeast could have been known in 1200 B.C.
Summarize Argument: Counter-Position
Campisi concludes that Yang is not justified in inferring that yeast was known as a leaven in 1200 B.C. just because leavens were known at that time. Why? Because, according to Campisi, other leavens than yeast could have been known in 1200 B.C.
Describe Method of Reasoning
Campisi undermines Yang’s conclusion by introducing an alternative explanation to account for Yang’s evidence. The evidence only shows that some unspecified leaven was used in 1200 B.C., so by pointing out the possibility that other leavens than yeast could have been known at that time, Campisi offers an alternative explanation.
A
suggesting that an alternative set of evidence better supports Yang’s conclusion
Campisi isn’t trying to support Yang’s conclusion, but rather to undermine it. Also, Campisi never proposes alternative evidence.
B
questioning the truth of a presumption underlying Yang’s argument
Yang presumes that there are no alternative leavens other than yeast that could have been known in 1200 B.C. By introducing other leavens as an alternative explanation for Yang’s evidence, Campisi questions that presumption.
C
denying the truth of Yang’s conclusion without considering the reason given for that conclusion
Campisi does consider the evidence behind Yang’s conclusion, and rejects its support for Yang’s conclusion on the grounds that there are alternative explanations available. Also, Campisi never denies the truth of Yang’s conclusion—unsupported doesn’t mean false.
D
pointing out that the premises of Yang’s argument more strongly support a contrary conclusion
Campisi does not argue that another specific conclusion is supported by Yang’s premises, only that Yang’s conclusion is not convincing based on its premises.
E
calling into question the truth of the evidence presented in Yang’s argument
Campisi does not question the evidence that a leaven was known in 1200 B.C., only offers alternative possible explanations for that evidence in order to question Yang’s conclusion.
Summarize Argument
The researcher concludes that watching too much TV increases the risk of developing personality disorders. He supports this by saying that people with certain personality disorders have more theta brain waves, and watching TV increases theta brain waves.
Identify and Describe Flaw
This is the cookie-cutter flaw of assuming that correlation proves causation. The researcher points out a correlation between theta brain waves and personality disorders, then assumes that theta brain waves cause those disorders. He concludes that since TV increases theta brain waves, it must also increase the risk of personality disorders.
In reality, personality disorders might cause the increase in theta waves, or another factor could be causing both. In either of these cases, the researcher’s link between watching TV and developing personality disorders falls apart.
A
uses the phrase “personality disorders” ambiguously
The researcher uses the phrase “personality disorders” clearly and consistently. Its meaning doesn’t shift throughout his argument.
B
fails to define the phrase “theta brain waves”
The researcher doesn't define “theta brain waves,” but he doesn’t need to. (B) doesn’t describe why his reasoning is questionable.
C
takes correlation to imply a causal connection
The author takes the correlation between theta brain waves and certain personality disorders to imply that theta brain waves cause those disorders. It’s possible, however, that the personality disorders cause theta brain waves or that some other factor causes them both.
D
draws a conclusion from an unrepresentative sample of data
We don’t know the sample size of the researcher’s data and we can’t simply assume that his data is unrepresentative.
E
infers that watching TV is a consequence of a personality disorder
Actually, the researcher infers that developing a personality disorder could be a consequence of watching TV. (E) has this backward.