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#27842
Complete Question Explanation

Evaluate the Argument. The correct answer choice is (A)

This stimulus presents information about a traffic accident. From prior investigation, it is known that at least one of the following factors was in play: The driver of the first vehicle did not signal prior to changing lanes, and/or the driver of the second vehicle was speeding. Either of these two would make a driver liable for the resulting accident, as follows:
  • Driver One signaled :arrow: Driver Two speeding :arrow: Driver Two Liable

    Driver Two speeding :arrow: Driver One signaled :arrow: Driver One Liable
It is known that the driver of the first vehicle was changing lanes without signaling. Based on this premise, the author of the stimulus improperly concludes that the driver of the second vehicle must not be liable, based on the following flawed reasoning:
  • Driver One signal :arrow: Driver One Liable :arrow: Driver Two Liable
This is a mistaken negation of the first conditional rule diagrammed above. We do know that if Driver Two wasn’t speeding, then Driver One must have been at fault, but we cannot logically conclude that if Driver One was at fault, that Driver Two must not have been speeding.

The conclusion that Driver Two is liable is flawed, because the conditional reasoning in the stimulus would allow for shared liability—that is, we know that if one driver isn’t liable, the other one must be, but we cannot conclude the reverse: that if one driver is liable, the other one isn’t. The question stem asks which answer choice provides the most important information for evaluating the author’s conclusion. As we can see from the original conditional statements offered in the stimulus, the only provided method to determine Driver Two’s liability concerns that driver’s speed.


Answer choice (A): This is the correct answer choice. If the driver of the second vehicle was driving at an excessive speed, then we could properly conclude that the second driver shares in the liability:
  • Driver Two speeding :arrow: Driver Two Liable
This is the only information, based on the conditional reasoning in the stimulus, that would allow us to draw such a conclusion.

Answer choice (B): The first driver’s knowledge of the infraction is immaterial to the question of causality. Unwitting or not, it is the failure to signal that would attach liability for the resulting accident.

Answer choice (C): The involvement of other drivers is also immaterial to the question of liability on the part of the two drivers that we know were involved. The stimulus tells us that “it is known” that either the driver of the first vehicle did not properly signal a lane change or that the driver of the second vehicle was speeding, and that either of these would result in a driver’s liability for the resulting accident. The involvement of other vehicles is not relevant to the conditional reasoning provided in the stimulus.

Answer choice (D): If a witness is unreliable, then any conclusions based on premises this witness establishes might also be unreliable. But the stimulus states that “further evidence has proved that the turn signal was not on, though the driver of that vehicle admits to having changed lanes.” The reliability of the first driver is therefore not at issue, and knowledge of the information from this answer choice would lend no insight into the evaluation of the author’s conclusion.

Answer choice (E): The stimulus specifically states that, absent excessive speed by the second driver, failure to signal would be the sole cause of the resulting accident. Thus, whether the second driver would have seen the signal is irrelevant.
 LAWSCHOOL22
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#81593
I was stuck between A and D on this because I thought that if the driver of the first vehicle was NOT a reliable witness, then we cannot assume that the driver of the first vehicle actually changed lanes. So, I thought that D had to be important to know in order to keep the conclusion intact. Can someone explain the error in my reasoning? Thank you!
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 KelseyWoods
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#81606
Hi LawSchool22!

It would be a little strange for a driver to say they changed lanes if they didn't. We'd be more concerned about the reliability of the first driver if we had to rely on them to tell us whether or not they signaled. But the stimulus says that evidence proves that the signal was not on, so we don't have to rely on the driver for that information.

But even if we accept that maybe the driver might lie about changing lanes when they didn't (false confessions happen!), answer choice (D) still wouldn't be as useful for evaluating this argument as answer choice (A). Try the Variance Test here: the two polar opposite answers to whether the driver of the first vehicle was a reliable witness are: Yes, they are a reliable witness; and No, they are not a reliable witness. If we say that the driver is not a reliable witness, that still doesn't necessarily mean that the driver is lying about changing lanes--unreliable witnesses can sometimes give accurate information. Also, if we say that the driver is a reliable witness, that really has no impact on the argument because we still don't know whether or not the second driver was speeding. The conclusion that we are trying to evaluate is that the driver of the second vehicle is not liable for the accident. Knowing that the first driver is reliable when they say they changed lanes without signaling and, thus, bear some liability for the accident really has nothing to do with whether or not the second driver was also liable for the accident because both drivers could be liable for the accident.

Here's a blog post that discusses the Variance Test in more detail: https://blog.powerscore.com/lsat/how-to ... tion-type/

Hope this helps!

Best,
Kelsey

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