LSAT 131 | Section 3 | Logical Reasoning: Q16

LR Question 16 Explanation

QUESTION TEXT: A common genetic mutation that lowers levels of the enzyme

QUESTION TYPE: Necessary Assumption

CONCLUSION: We can eliminate periodontitis once researchers figure out how to restore cathepsin C levels to normal.

REASONING: Lack of the enzyme cathepsin C is a cause of periodontitis.

ANALYSIS: The author lists one cause of periodontitis and assumes without proof that it is the only possible cause.

Note that scientific questions are often quite simple. Don’t let the fancy words frighten you.

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1. It doesn’t matter if this is the only way. The author was only arguing that it is a way to eliminate periodontitis. The existence of other methods doesn’t harm the argument.
   Negation: One additional method of eliminating periodontitis would be inventing godlike superpowers and changing the structure of the universe.
2. The author didn’t say that researchers were going to fix the genetic mutation. They just said the researchers would restore enzyme levels. So this might work in cases where people lost the enzyme for non-genetic reasons as well.
3. The author didn’t say “this will happen soon”. They just said “Once that happens.” It could happen in 1000 years and that wouldn’t harm the argument.
4. This isn’t necessary. The author only said that lack of cathepsin C can cause gum disease. It doesn’t matter why the levels are low: genetics were just an example of how cathepsin C could be low.
5. CORRECT. See the analysis above. If people with normal levels of cathepsin C can also get gum disease, then fixing the enzyme won’t be enough to cure gum disease.
   Negation: You can get gum disease even if researchers have restored your cathepsin C levels to normal.