Logical reasoning PrepTest 155 · Section 1 · Question 7

Knowing that large trucks do not use studded snow tires ever might strengthen this argument. It would rule out the possibility that large trucks and studded snow tires together contribute to ruts' formation. That would lend further credence to the claim that only one causes ruts, and since we know ruts appear only in the areas that allow studded snow tires, that would strengthen the idea that studded snow tires are to blame. But ... that's not what this answer choice says. This answer choice merely claims that large trucks cannot have studded snow tires in many (read: some) areas. That allows the possibility that the "many places" this official references permit large trucks to use studded snow tires. And that could weaken this argument by allowing for the possibility that large trucks and studded snow tires together contribute to ruts' formation. It's always worth remembering that answer choices with weak, wishy-washy language like "many" will seldom strengthen an argument — especially a causal argument.

This weakens the argument by showing the cause appearing without the effect. If truck traffic diminished while studded snow tires remained and the number of ruts declined, then it seems far more likely that the trucks, and not the studded snow tires, were causing the ruts.

Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
A transportation official doesn't believe that large trucks are responsible for ruts in the local roads. Why? There are places with the same amount of snowfall and large-truck traffic as the official's city, but only those cities that allow studded snow tires have ruts like the official's city. So the studded snow tires are the real rut-causers.

Strategy Overview:

1. Argument or facts? Always argument, so identify premises and conclusions of argument
2. Anticipate why the premises are not enough to show that the conclusion is true
   1. Causal argument? Look for answer choice that:
      1. Rules out possible alternate cause
      2. Shows same cause, same effect
      3. Shows no cause, no effect
      4. Shows the cause and effect are not reversed
3. If not causal argument, anticipate ways to fix problem with argument
4. Use anticipations to select the answer choice that, if true, would strengthen argument

Answer Anticipation:
On Strengthen questions, the correct answer usually helps fix a flaw in the argument. This is why we should try to identify a problem with the argument first. Once we identify the problem, we're better equipped to pick an answer choice that fixes that problem.

Causation flaws are among the more common on Strengthen (and Weaken!) questions, and this is undoubtedly a causal argument: studded snow tires, not large trucks, caused ruts in this area's roads. ("Blame" is our causal indicator word here.)

Once we've identified the causation flaw in this question, we can anticipate a few ways the correct answer may strengthen it. The passage mentioned a possible alternate cause (large trucks), so the correct answer might further rule out large trucks as the culprit. The correct answer might also show the cause and effect arent' reversed by explaining that the ruts in the road aren't the reason people use studded snow tires. Although the passage already provided examples of "same cause, same effect" (we see the ruts in areas in which studded snow tires are used), the correct answer could provide another example of that. Another likely possibility is providing an instance of "no cause, no effect," particularly because the passage hasn't already provided such an example. The correct answer may show that places with large trucks but few studded snow tires have very few ruts.

It's also worth mentioning that the correct answer could strengthen this argument by weakening the possibility that trucks are to blame. So we could get an example of "cause without the effect" (many large trucks and few ruts) or "effect without the cause" (many ruts and few large trucks).

Answer Choice Explanation:
A perfect match for the anticipation of "further ruling out the alternate cause." If you can have ruts without any meaningful large truck traffic, large trucks are probably not the primary cause of ruts. (This is an example of "effect without the cause," which will always weaken the persuasiveness of a purported cause.) This answer choice strengthens the conclusion and is correct.

Key Takeaway:
Sometimes causal arguments on the LSAT come complete with an alternate cause already proposed. When this is the case, correct answer choices will often focus on further supporting or opposing that alternate cause, depending on what type of question you're doing. Here, the correct answer weakened the likelihood that the alternative cause led to the ruts' formation. A good reminder to always pay attention to potential alternate causes mentioned in causal arguments!

Without knowing more about the prevalence of studded snow tires or ruts in these cities, we can't evaluate whether or not this would strengthen or weaken the conclusion. If these cities didn't allow studded snow tires and had far fewer ruts, this could strengthen the argument (by providing an example of "no cause, no effect"). If these cities didn't allow studded snow tires and had far more ruts, this would weaken the argument (by providing an example of "effect without the cause"). If these cities permitted studded snow tires and had the same number or more ruts, we couldn't say what the effect is — we'd still have the pesky truck-traffic variable, and we couldn't know the cause was the trucks or studded snow tires or both. In other words, this answer choice doesn't give us enough information to conclude its effect on the argument.

This is irrelevant to the argument, because we know that our transportation official lives in an area that does have snowfall and does allow studded snow tires. Unless we also knew that cities had no ruts similar to the official's city, we can't say it strengthens the argument.