Logical reasoning PrepTest 131 · Section 3 · Question 16

Incorrect. Even if there's another way to eliminate periodontitis, raising enzyme C levels might also work. The argument concludes that a certain method will work, so it doesn't need to assume that nothing else will also work.

Incorrect. This is a very tempting answer, but it's off for a subtle reason. Even if there are other causes of low enzyme C, the cure in question increases enzyme levels directly, not through the genetic mutation. So if there's, say, a viral cause of lower levels of enzyme C, this cure could still work since it's increasing enzyme levels.

Incorrect. Note the opening clause in the conclusion—"Once that happensÉ" Since the conclusion is conditioned on researchers succeeding, it's not assuming that they are. Additionally, the conclusion doesn't have a timeline attached, so this answer choice stating that researchers will "soon" succeed is not necessary.

Incorrect. This is another very tempting trap answer! Rephrasing the double negative here, this answer choice states that those without the genetic mutation are immune to gum disease. However, that's not necessary for the argument to work—even if those without the genetic mutation can get periodontitis, it's possible that raising their enzyme C level would still cure that disease.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Cause: Genetic mutation that lowers enzyme C levels
Effect: Reduced ability to fight gum disease
Solution: Restore enzyme C to normal levels
Conclusion: Once restored, periodontitis will be eliminated

Answer Anticipation:
As with any argument that features a causal conclusion (since the conclusion is about a cure, it's inherently causal), we should start by thinking about a correlation/causation flaw. However, in this case, the premises are causal—the genetic mutation "lowers" enzyme C levels and "reduces" the ability to fight gum disease. Since the causal conclusion is based on a related causal premise, there's no correlation/causation flaw here.

Next, we should focus on that extreme word in the conclusion—"eliminate." In order to eliminate something, there has to be none of it left. While the argument has highlighted that a genetic mutation lowering enzyme C levels is a cause of gum disease, it doesn't establish that there are no other causes. If there are, and those other causes aren't also addressed by raising enzyme C level, then this one method won't eliminate periodontitis. Even in the case of those with the genetic mutation, there's no indication that restoring enzyme C levels will serve as a cure—maybe the damage is already done, and restoring those levels won't prevent gum disease in those who were born with the genetic mutation.

In any case, the flaw in this argument is that it establishes one potential cure for a disease and treats it as if it's going to prevent all cases of that disease, so any answer that rules out the possibility someone could suffer from periodontitis after this cure is rolled out is necessary to reach the conclusion about the elimination of the disease.

Answer Explanation:
This answer eliminates the possibility that someone who started with low enzyme C but had it increased would still have periodontitis—i.e., the damage was already done, and so periodontitis wouldn't be "eliminated." If a person with low C levels that have been restored will still suffer from periodontitis, then periodontitis won't be eliminated after researchers find a way to restore those levels.

Key Takeaway:
This causal argument is based on a causal premise, which meant that a correlation/causation flaw wasn't present, but it introduced an interesting new wrinkle. When dealing with alternative potential causes, the additional causal step (genetic mutation caused low enzyme levels caused periodontitis) cut out an avenue of potential answer related to an alternative cause of the low enzyme levels to begin with since the cure went straight after them—a cause of periodontitis, but an effect of something else. What can we learn from this? When looking at a causal conclusion, deal with the direct causal connection in thinking about alternatives, not earlier steps in the causal chain.