Motorcoach driver: Professional drivers spend much more time driving, on average, than do other people and hence are more competent drivers than are other, less experienced drivers. Therefore, the speed limit on major highways should not be reduced, because that action would have the undesirable effect of forcing some people who are now both law-abiding and competent drivers to break the law.

Police officer: All drivers can drive within the legal speed limit if they wish, so it is not true to say that reducing the speed limit would be the cause of such illegal behavior.

Speaker 1 Summary

The motorcoach driver claims that we shouldn’t reduce highway speed limits. Why not? Because doing so would “force” some competent drivers to break the law, presumably by speeding. Who would these drivers be? We can infer the motorcoach driver is talking about professional drivers, who are better-than-average drivers because they spend more time driving. (The assumption is that the professionals wouldn’t reduce their speed to respect a new limit.)

Speaker 2 Summary

The police officer argues that lowering the speed limit would not actually be the cause of people speeding. This is because anyone can drive at the limit if they choose to—so the drivers’ choices, not the limit, would be to blame for speeding.

Objective

We need to find a point of disagreement. The driver and the officer disagree about whether lowering the speed limit would cause any drivers to speed.

A
it would be desirable to reduce the speed limit on major highways

The motorcoach driver disagrees with this, but the police officer doesn’t state an opinion. The police officer never mentions whether or not we should change the speed limit.

B
professional drivers will drive within the legal speed limit if that limit is reduced

The motorcoach driver disagrees with this, but the police officer neither agrees nor disagrees. The police officer doesn’t say whether professional drivers actually will speed; the point is just that if they did so it would be their own fault.

C
reducing the speed limit on major highways would cause some professional drivers to break the law

The motorcoach driver agrees with this, but the police officer disagrees, so this is the point at issue. The police officer claims that the cause of speeding would not be the lower limit, but would instead be that the drivers chose to speed.

D
professional drivers are more competent drivers than are other, less experienced drivers

The motorcoach driver agrees with this, but the police officer doesn’t state an opinion. The police officer doesn’t say anything at all about the competency of professional versus non-professional drivers.

E
all drivers wish to drive within the speed limit

Neither speaker states an opinion about this claim. Neither the motorcoach driver nor the police officer makes any kind of statement about what drivers actually wish to do.


6 comments

Because of the lucrative but illegal trade in rhinoceros horns, a certain rhinoceros species has been hunted nearly to extinction. Therefore an effective way to ensure the survival of that species would be to periodically trim off the horns of all rhinoceroses, thereby eliminating the motivation for poaching.

Summary
The argument concludes that a certain near-extinct rhinoceros species could be saved by regularly trimming the horns of all rhinos. How would this help? Because the reason that the species is endangered is because of poachers trading in rhino horns, and trimming the horns would remove the motivation for poaching.

Notable Assumptions
The argument assumes that resolving the cause that initially led to this species becoming endangered would be enough to allow the species’ survival going forward. In other words, the species hasn’t reached a point where even eliminating poaching won’t save it.
The argument also assumes that trimming the rhinos’ horns wouldn’t have unexpected consequences that could further endanger the species, such as making the rhinos more vulnerable to predators or lowering their reproductive rate.

A
Most poachers who are discouraged from hunting rhinoceroses are not likely to hunt other animals for their horns.
The argument is only concerned with ensuring the survival of this rhino species, so it’s not necessary that other animals will not become endangered.
B
At least some rhinoceroses whose horns are periodically trimmed off will be able to attract mates.
In order for the rhino species to survive, the members of the species must be able to reproduce. If trimming their horns totally prevented the rhinos from finding mates, they would go extinct even without poachers. That’s why this assumption is necessary.
C
Poachers hunt at least some immature rhinoceroses whose horns have not yet started to develop.
Ensuring the species’ survival doesn’t require protecting every single member of the species from hunting, so this assumption isn’t necessary.
D
The demand for rhinoceros horns will remain constant even if the supply decreases after the periodic trimming-off of the rhinoceros horns has begun.
Whatever happens to the demand for rhino horns is irrelevant, especially given the premise that trimming rhino horns would eliminate the motivation to continue poaching.
E
Rhinoceroses whose horns have been trimmed off are unable to defend themselves against predators.
Far from being necessary, this assumption would undermine the argument. In fact, it’s the exact opposite of one possible necessary assumption: that rhinos with trimmed horns would be able to defend themselves.

58 comments

Herbalist: Many of my customers find that their physical coordination improves after drinking juice containing certain herbs. A few doctors assert that the herbs are potentially harmful, but doctors are always trying to maintain a monopoly over medical therapies. So there is no reason not to try my herb juice.

Summarize Argument: Counter-Position
The herbalist concludes that there’s no reason not to try drinking herb juice, even though some doctors say it might be harmful. According to the herbalist, doctors just want to keep a monopoly on medical treatments, implying that we should ignore them.

Identify and Describe Flaw
This is a cookie-cutter ad hominem flaw. The herbalist attacks the doctors’ character to try to discredit them instead of addressing the actual claim the doctors are making.

A
attempts to force acceptance of a claim by inducing fear of the consequences of rejecting that claim
The herbalist doesn’t bring up any consequences of rejecting the claim that herb juice is safe to drink.
B
bases a conclusion on claims that are inconsistent with each other
The herbalist never makes any claims that are inconsistent with each other.
C
rejects a claim by attacking the proponents of the claim rather than addressing the claim itself
The herbalist rejects the doctors’ claim that herb juice may be dangerous by attacking the doctors’ motives, and doesn’t address the possibility of herb juice being dangerous. However, the doctors’ claim might still be accurate regardless of their motives.
D
relies on evidence presented in terms that presuppose the truth of the claim for which the evidence is offered
The herbalist’s evidence, that doctors have ulterior motives, does not presuppose the truth of the conclusion that there’s no reason not to try herb juice.
E
mistakes the observation that one thing happens after another for proof that the second thing is the result of the first
The herbalist isn’t discussing any two events that happen one after the other, nor does the argument propose a causal relationship.

11 comments

A company with long-outstanding bills owed by its customers can assign those bills to a collection agency that pays the company a fraction of their amount and then tries to collect payment from the customers. Since these agencies pay companies only 15 percent of the total amount of the outstanding bills, a company interested in reducing losses from long-outstanding bills would be well advised to pursue its debtors on its own.

Summary
The argument concludes that companies with long-outstanding debts would better reduce their losses by going after their debtors than by selling the debts to collection agencies. In support, the argument claims that collection agencies only pay 15 percent of the amount debtors owe.

Notable Assumptions
The argument assumes that the companies in question would recover more than 15 percent of the outstanding debts if they went after the debtors themselves. It also assumes that it wouldn’t cost companies so much to recover the debts that they would net less than 15 percent of the amount owing.
Without these assumptions, there’s no way that companies could reduce their losses by collecting debts themselves compared to selling the debts.

A
a company that pursues its debtors on its own typically collects more than 15 percent of the total amount of the long-outstanding bills that it is owed
This is necessary a company to reduce its losses more by pursuing debtors itself, rather than by selling the debts for 15 percent of their amount. In other words, this is necessary for pursuing debtors to be the financially wiser option.
B
the cost to a company of pursuing its debtors on its own for payment of long-outstanding bills does not exceed 15 percent of the total amount of those bills
Without knowing what percentage of the debt a company would actually collect, this isn’t necessary. For example, if a company collects 50 percent of its debts but spends 20 percent of the amount owed, that’s still way better than selling the debt for 15 percent.
C
collection agencies that are assigned bills for collection by companies are unsuccessful in collecting, on average, only 15 percent of the total amount of those bills
The amount that a collection agency is able to recover is irrelevant to how much a company would be able to recover when pursuing debts itself. We can’t assume that companies would recover the same amount as do collection agencies.
D
at least 15 percent of the customers that owe money to companies eventually pay their bills whether or not those bills are assigned to a collection agency
15 percent of customers paying their bills isn’t relevant to us, because we don’t know what proportion of the total debt is owed by those customers.
E
unless most of the customers of a company pay their bills, that company in the long run will not be profitable
This is irrelevant—the argument isn’t concerned with profitability and customers paying their bills, but only with the best way to approach long-outstanding debts.

23 comments

Carl: Researchers who perform operations on animals for experimental purposes are legally required to complete detailed pain protocols indicating whether the animals will be at risk of pain and, if so, what steps will be taken to minimize or alleviate it. Yet when human beings undergo operations, such protocols are never required. If lawmakers were as concerned about human beings as they seem to be about animals, there would be pain protocols for human beings too.

Debbie: But consider this: a person for whom a doctor wants to schedule surgery can simply be told what pain to expect and can then decide whether or not to undergo the operation. So you see, pain protocols are unnecessary for human beings.

Summarize Argument
Debbie argues that pain protocols are unnecessary for humans. This is because, unlike animals, humans can be told how much pain to expect and simply choose not to undergo the surgery.

Notable Assumptions
Debbie assumes that humans can choose not to undergo a surgery, which seems to neglect essential surgeries or surgeries on people who can’t make choices for themselves. Debbie also assumes a principle: if humans can choose not to have a surgery performed given the pain involved, no pain protocol should be put in place.

A
Not all operations that are performed on human beings are painful.
We’re talking about the operations that are painful. Why don’t those require pain protocols?
B
Some experimentation that is now done on animals need not be done at all.
Debbie doesn’t argue about how experimentation should be done on animals.
C
Preparing pain protocols is not a time-consuming or costly procedure.
Debbie doesn’t claim pain protocols are too expensive and time-consuming.
D
Some surgical operations performed on infants are painful.
Infants can’t decide to forego a surgery. This weaken’s Debbie’s claim that humans can choose not to undergo a surgery based on how much pain will be involve, since evidently some humans can’t make that choice.
E
Unalleviated pain after an operation tends to delay the healing process.
We don’t care about pain after an operation. We’re concerned with painful surgeries.

74 comments

Carl: Researchers who perform operations on animals for experimental purposes are legally required to complete detailed pain protocols indicating whether the animals will be at risk of pain and, if so, what steps will be taken to minimize or alleviate it. Yet when human beings undergo operations, such protocols are never required. If lawmakers were as concerned about human beings as they seem to be about animals, there would be pain protocols for human beings too.

Debbie: But consider this: a person for whom a doctor wants to schedule surgery can simply be told what pain to expect and can then decide whether or not to undergo the operation. So you see, pain protocols are unnecessary for human beings.

Summarize Argument: Counter-Position
Debbie concludes that pain protocols are unnecessary for humans. As evidence, she points out that humans are able to communicate directly with doctors and decide from there whether they will undergo an operation.

Describe Method of Reasoning
Debbie counters the position held by Carl. She does this by pointing out a crucial difference between human beings and animals: human beings are capable of communicating and deciding for themselves, whereas animals are not.

A
showing that one of the claims on which Carl bases his conclusion is inaccurate
Debbie never claims that any of Carl’s premises are inaccurate. Rather, Debbie questions Carl’s conclusion by pointing out additional evidence Carl’s argument does not consider.
B
pointing out a relevant difference to undermine an analogy on which Carl bases his conclusion
The relevant difference is between that of human beings and animals. Debbie states that human beings are capable of being told about what pain to expect and make their own decisions. The animals in Carl’s analogy are incapable of these things.
C
claiming that Carl’s argument should be rejected because it is based on an appeal to sentimentality rather than on reasoned principles
Carl’s argument is not an appeal to sentimentality. Rather, his argument is an appeal to analogy.
D
drawing an analogy that illustrates a major flaw in Carl’s argument
Debbie does not draw an analogy. Carl draws an analogy between human beings and animals, and Debbie rejects this analogy by pointing out a relevant difference between the two.
E
offering a specific example to demonstrate that Carl’s argument is based on a claim that can be neither confirmed nor disproved
Debbie concludes that pain protocols for human beings are unnecessary.

7 comments

Ornithologist: The curvature of the claws of modern tree-dwelling birds enables them to perch in trees. The claws of Archeopteryx, the earliest known birdlike creature, show similar curvature that must have enabled the creature to perch on tree limbs. Therefore, Archeopteryx was probably a tree-dwelling creature.

Paleontologist: No, the ability to perch in trees is not good evidence that Archeopteryx was a tree-dwelling bird. Chickens also spend time perched in trees, yet chickens are primarily ground-dwelling.

Summary
The ornithologist concludes that Archeopteryx probably lived in trees. This is supported by an analogy to modern tree-dwelling birds, whose curved claws let them perch in trees. Archeopteryx also had curved claws, leading to the sub-conclusion that Archeopteryx must also have been able to perch in trees.

Notable Assumptions
The ornithologist goes from evidence about Archeopteryx’s ability to perch in trees to a conclusion that Archeopteryx probably lived in trees. This requires assuming that Archeopteryx’s ability to perch in trees indicates Archeopteryx having actually spent time in trees.

A
Modern tree-dwelling birds are the direct descendants of Archeopteryx.
Whether or not modern tree-dwelling birds directly descended from Archeopteryx isn’t relevant to whether Archeopteryx actually spent time in trees.
B
Archeopteryx made use of the curvature of its claws.
In other words, Archeopteryx truly spent time perching in trees, enabled by its curved claws. This is necessary to assume, because if Archeopteryx didn’t use its claws to perch in trees, then its claws don’t support the theory that it was tree-dwelling.
C
There have never been tree-dwelling birds without curved claws.
Whether or not curved claws are truly necessary to tree-dwelling birds is irrelevant to whether Archeopteryx’s curved claws support the theory that it lived in trees.
D
Archeopteryx was in fact the earliest birdlike creature.
The ornithologist’s argument just concerns Archeopteryx’s behavior, so it’s totally irrelevant whether there were unknown earlier birdlike creatures.
E
The curvature of the claws is the only available evidence for the claim that Archeopteryx was tree-dwelling.
Whether or not there’s other evidence of Archeopteryx living in trees isn’t relevant to whether the evidence of curved claws truly supports the ornithologist’s theory that Archeopteryx lived in trees.

16 comments

Ornithologist: The curvature of the claws of modern tree-dwelling birds enables them to perch in trees. The claws of Archeopteryx, the earliest known birdlike creature, show similar curvature that must have enabled the creature to perch on tree limbs. Therefore, Archeopteryx was probably a tree-dwelling creature.

Paleontologist: No, the ability to perch in trees is not good evidence that Archeopteryx was a tree-dwelling bird. Chickens also spend time perched in trees, yet chickens are primarily ground-dwelling.

Summarize Argument: Phenomenon-Hypothesis
The paleontologist concludes that, contrary to the ornithologist’s hypothesis, Archeopteryx may not have been a tree-dwelling bird. As evidence, the paleontologist points out that chickens spend time perched in trees, but are primarily ground-dwelling birds.

Describe Method of Reasoning
The paleontologist points out a weakness in the ornithologist’s hypothesis by presenting an analogy. By stating chickens are primarily ground-dwelling birds, the paleontologist shows that having curved claws is not sufficient evidence to conclude a bird is tree-dwelling.

A
questions the qualifications of the ornithologist to evaluate the evidence
The paleontologist never questions the ornithologist’s qualifications. Rather, the paleontologist simply claims that the ornithologist’s evidence is not sufficient.
B
denies the truth of the claims the ornithologist makes in support of the hypothesis
The paleontologist does not deny the truth of the ornithologist’s evidence. The paleontologist does not deny that curved claws enable birds to perch in trees, nor does he deny that Archeopteryx could perch in trees.
C
uses a parallel case to illustrate a weakness in the ornithologist’s argument
The parallel case the paleontologist uses is the case of chickens. Chickens have curved claws and can perch themselves in trees, but are primarily ground-dwelling birds.
D
shows that the hypothesis contradicts one of the pieces of evidence used to support it
The paleontologist does not claim that the ornithologist’s hypothesis contradicts a premise. Rather, the paleontologist claims that the ornithologist’s premises are not sufficient to support their hypothesis.
E
provides additional evidence to support the ornithologist’s argument
The paleontologist does not support the ornithologist’s argument. The paleontologist begins by denying the sufficiency of the ornithologist’s evidence.

8 comments

A commonly accepted myth is that left-handed people are more prone to cause accidents than are right-handed people. But this is, in fact, just a myth, as is indicated by the fact that more household accidents are caused by right-handed people than are caused by left-handed people.

Summarize Argument: Counter-Position

The argument concludes that left-handed people are not more prone to cause accidents than right-handed people. This is supported by the point that more household accidents are caused by right-handed people than by left-handed people.

Identify and Describe Flaw

The argument is flawed because it confuses percentages and amounts. The claim that right-handed people cause a greater number of accidents doesn’t disprove that left-handed individuals are more prone to accidents. If most people are right-handed, then left-handed people may still cause more accidents relative to their population size, making them more prone to accidents.

A
makes a distinction where there is no real difference between the things distinguished

The only distinction the argument makes is between left-handed and right-handed people, where there is a real difference.

B
takes no account of the relative frequency of left-handed people in the population as a whole

The argument concludes that left-handed people aren’t more prone to accidents, but its support only addresses the number of accidents caused by left- and right-handed people. Without knowing the percentage of different-handed people, that evidence can’t support that conclusion.

C
uses the word “accidents” in two different senses

The argument uses “accidents” in a consistent sense. When the term “accidents” is used, it’s always referring to unintentional incidents that cause some kind of damage.

D
ignores the possibility that some household accidents are caused by more than one person

This possibility wouldn’t have any effect on the argument. We would still be accounting for all the left- and right-handed people involved in causing household accidents, even if they weren’t the sole cause.

E
gives wholly irrelevant evidence and simply disparages an opposing position by calling it a “myth”

The argument does give relevant evidence about the frequency of accidents caused by right- and left-handed people. It’s just missing clarifying evidence about the size of the right- and left-handed populations.


34 comments