Multiple sclerosis is an autoimmune disease: white blood cells attack the myelin sheath that protects nerve fibers in the spinal cord and brain. Medical science now has a drug that can be used to successfully treat multiple sclerosis, but the path that led medical researchers to this drug was hardly straightforward. Initially, some scientists believed attacks characteristic of multiple sclerosis might be triggered by chronic viral infections. So in 1984 they began testing gamma interferon, one of the body’s own antiviral weapons. To their horror, all the multiple sclerosis patients tested became dramatically worse. The false step proved to be instructive however.
Summary
Scientists thought multiple sclerosis (MS) was caused by viral infections. To test this hypothesis, they used gamma interferon—a tool the body uses to combat viral infections—to treat MS. This experiment, however, resulted in the MS patients’ conditions worsening.
Notable Valid Inferences
Gamma interferon makes MS worse.
A
Gamma interferon stops white blood cells from producing myelin-destroying compounds.
This is not compatible with the experiment’s results. If gamma interferon does what (A) claims, it would interfere with the mechanism that makes MS so destructive. This would likely improve MS patients’ conditions—this contradicts the experiment, which shows the opposite effect.
B
Administering gamma interferon to those without multiple sclerosis causes an increase in the number of white blood cells.
This could be true and may explain why gamma interferon makes MS patients’ conditions worse. By causing an increase in white blood cells, gamma interferon could increase the number of cells attacking the myelin sheath in MS patients.
C
Medical researchers have discovered that the gamma interferon level in the cerebrospinal fluid skyrockets just before and during multiple sclerosis attacks.
This could be true and may explain why gamma interferon makes MS patients’ conditions worse. It suggests an association between increased gamma interferon levels and MS attacks.
D
It has now been established that most multiple sclerosis sufferers do not have chronic viral infections.
This could be true. It suggests that scientists’ initial belief that MS is triggered by viral infections is incorrect. This could explain why gamma interferon, one of the body’s antiviral tools, is ineffective against it.
E
The drug now used to treat multiple sclerosis is known to inhibit the activity of gamma interferon.
This could be true and may explain why gamma interferon makes MS patients’ conditions worse. It suggests that inhibiting gamma interferon levels improves patients’ conditions—this is consistent with the finding that increasing gamma interferon levels worsens patients’ conditions.
Summarize Argument
The economist argues that we should not assume that the profit motive is to blame for any homelessness that results from a lack of housing. (Homelessness resulting from other causes is not addressed in this argument.) The reason, the economist says, is that investors do actually build housing if they can profit from it. The conclusion is further supported by a claim that it’s unrealistic to ask investors to build housing in a poor market. This all suggests that market conditions may be the cause of insufficient housing, not the profit motive.
Identify Argument Part
The phrase “To the extent that homelessness arises from a lack of available housing” defines the scope of the argument: the economist is only discussing the portion of homelessness caused by lack of housing, not any remainder arising from other causes.
A
It limits the application of the argument to a part of the problem.
This is exactly what the phrase identified does. It tells us that the economist’s argument only focuses on some situations of homelessness, meaning that the argument needn’t address every single case—only those caused by a housing shortage.
B
It suggests that the primary cause of homelessness is lack of available housing.
The phrase identified never compares lack of available housing with any other causes of homelessness, nor does it say one is a greater cause than the other. In fact, nothing in the argument does this.
C
It is offered as evidence crucial to the conclusion.
The phrase identified doesn’t support the conclusion, just limits its scope. Just saying that some homelessness may arise from a lack of housing does not lead to the conclusion that the profit motive may not be to blame.
D
It expresses the conclusion to be argued for.
The argument is not designed to support the phrase identified. Nothing else the economist says implies that some homelessness is caused by housing shortage; instead, the argument supports a conclusion about the blameworthiness of the profit motive.
E
It suggests a possible solution to the problem of homelessness.
This is not something the argument does at all. The economist isn’t concerned with proposing solutions, and no part of the argument suggests how homelessness might be addressed.
Summarize Argument
The author concludes that beauty isn’t subjective. This is because earlier cultures’ beauty standards largely align with today’s.
Notable Assumptions
The author assumes that if today’s beauty standards align with those of early cultures, those beauty standards must be rooted in something objective rather than subjective. The author also assumes that we can know which works any given culture considered “most beautiful.” Finally, the author assumes that today’s beauty standards aren’t influenced by those of earlier cultures. If this were true, it would mean those standards are at least partially subjective.
A
Few contemporary artists have been significantly exposed to the art of earlier cultures.
We’re not concerned with contemporary artists. We need to know how people perceive beauty, and if that perception is rooted in something subjective or objective.
B
The arts held a much more important place in earlier cultures than they do in our culture.
It doesn’t matter how important the arts are to a given culture. We need to know about beauty.
C
Our own standard of beauty was strongly influenced by our exposure to works that were considered beautiful in earlier cultures.
If our standards of beauty today were influenced by older cultures, then those standards must be subjective. An objective, innate standard can’t be influenced by something else.
D
Much of what passes for important artistic work today would not be considered beautiful even by contemporary standards.
We need to know if our aesthetic reactions to earlier cultures’ art means that beauty is objective. This only talks about important artworks today.
E
In most cultures art is owned by a small social elite.
Ownership isn’t important. We’re concerned with how people judge and react to art.
Summarize Argument: Phenomenon-Hypothesis
The researcher hypothesizes that adequate prenatal care significantly reduces the risk of low birth weight babies. This is supported by an observed correlation from hospital records: mothers who receive inadequate prenatal care are more likely to have low birth weight babies than mothers who receive adequate prenatal care. The records also noted that premature babies are more likely to have low birth weights.
Notable Assumptions
The researcher assumes that there is no alternative cause accounting for the observed correlation between inadequate prenatal care and low birth weight. For example, social or economic factors might instead cause both.
The researcher also assumes that the hospital records give a complete and accurate picture of the situation. If the hospitals’ data entry is flawed, then even the correlation may not be reliable.
The researcher also assumes that the hospital records give a complete and accurate picture of the situation. If the hospitals’ data entry is flawed, then even the correlation may not be reliable.
A
The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.
Like (D), this does not weaken the researcher’s argument, because “many” normal birth weight babies being born despite inadequate prenatal care is totally consistent with an overall correlation between those factors. A statistic doesn’t require every individual case to match!
B
Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.
This weakens the researcher’s argument because it undermines the reliability of the hospital records. Premature babies usually have low birth weights, so this practice could easily skew the recorded correlation. And if the correlation isn’t solid, it’s hard to argue causation.
C
The hospital records indicate that low birth weight babies were routinely classified as having been born prematurely.
This does not weaken the researcher’s argument because, unlike (B), it does not affect the correlation between low birth weight and inadequate prenatal care. If the researcher’s hypothesis was about premature birth and low birth weight, this might weaken, but it’s not.
D
Some babies not born prematurely, whose mothers received adequate prenatal care, have low birth weights.
Like (A), this does not weaken the researcher’s argument, because the researcher is focusing on statistical trends, not individual cases. Even if “some” babies’ circumstances are different, that doesn’t mean the overall trend isn’t still reliable.
E
Women who receive adequate prenatal care are less likely to give birth prematurely than are women who do not receive adequate prenatal care.
This does not weaken the researcher’s argument because it’s completely consistent with adequate prenatal care preventing low birth weight. In fact, this suggests an indirect causation where premature birth acts as a mechanism for causing or preventing low birth weight.
Summarize Argument
The author claims that homeowners are generally unlikely to switch back to oil heating soon after having switched to natural gas due to its lower cost. Why? Because switching to gas in the first place required investing in new equipment, and presumably homeowners won’t want to duplicate that investment.
Notable Assumptions
The author assumes that the amount saved by continuing to use gas and not having to buy new oil-compatible equipment outweighs any savings from switching back to oil. In other words, equipment and oil have not gotten so much cheaper (and that gas hasn’t gotten so costly) that it would be worth switching again.
A
the price of natural gas to heat homes has remained constant, while the cost of equipment to heat homes with natural gas has fallen sharply
This does not weaken the argument, because it doesn’t challenge the author’s cost-benefit assumption. This gives us no reason to believe that oil heating now represents a cost savings over gas heating—we still don’t know which one is currently cheaper.
B
the price of home heating oil has remained constant, while the cost of equipment to heat homes with natural gas has risen sharply
This does not weaken the argument because it doesn’t indicate any kind of savings from switching back to oil. We’re only concerned with homeowners who currently use gas, so the cost of switching to gas is irrelevant. This also doesn’t tell us how oil and gas prices compare.
C
the cost of equipment to heat homes with natural gas has fallen sharply, while the price of home heating oil has fallen to 1970 levels
This does not weaken the argument. We’re not concerned with gas heating equipment prices, because we only care about current gas users. Like (E), the falling cost of oil is tempting, but we still don’t know how it compares with gas—maybe they both fell, and gas is still cheaper.
D
the cost of equipment to heat homes with oil has fallen sharply, while the price of heating with oil has fallen below the price of heating with natural gas
This weakens the argument because it indicates that oil is currently less expensive than gas, while also reducing the additional cost of getting new oil-heating equipment. This undermines the author’s cost-benefit assumption, thereby weakening.
E
the use of oil to heat homes has continued to decline, while the price of heating oil has fallen to 1970 levels
This does not weaken the argument, because like (C), just knowing that the cost of oil has fallen doesn’t actually tell us much: we still don’t know how oil and gas compare. The continued decline in oil heating also doesn’t do anything, because we don’t know why it’s happening.