#16 - A common genetic mutation that lowers levels of the

[James Finch]

Hi Rahim,

It looks like you're trying to take a contrapositive of a causal relationship, which we can't logically do. You're correct in that low levels of capthepsin C causes gum disease, and is the only cause given. From this, we can infer that the author definitely believes (E), that removing the cause (low level of capthepsin C) will then remove the effect as well (gum disease). However, do we know that the author believes this is the only way? What if a mouthwash were created that had a similar effect as raising CC to normal levels, but it used different substances to do it? It's still a possibility, as it's not excluded by anything in the stimulus.

The quickest and easiest way to eliminate (A), however, is to use the Assumption Negation technique: negate the answer choice, and see if that would lead logically to the negation of the conclusion as well. Here we would have:

"Restoring CC to normal levels is not the only way to eliminate periodontitis"

"Even after restoring CC to normal levels, we still will not be able to eliminate periodontitis"

This clearly doesn't make any sense. Contrast this to the negation of (E):

"A person whose cathepsin C level has been restored to normal will suffer from periodontitis."

"Even after restoring CC to normal levels, we still will not be able to eliminate periodontitis"

This flows perfectly, making it the correct answer choice.

Hope this clears things up!

[LSAT2018]

Restoring enzyme cathepsin C to normal levels eliminating periodontitis

This straightforward cause/effect reasoning links cathepsin C with eliminating periodontitis. So the correct answer choice will squarely address this relationship. Answer choice (E) fills in the gap between the cause and effect by assuring us that, once a person's cathepsin C levels reach a normal level, they will not have periodontitis. If restoring the cathepsin C levels did anything other than cure or prevent periodontitis, this researcher's argument wouldn't make any sense.

What is the difference between the assumption in answer (E) and the final two statements of the stimulus? The stimulus reads, 'But researchers are developing ways to restore the enzyme to normal levels. Once that happens, we will be able to eliminate periodontitis.' This does not sound very different from the answer, rather just a repeated statement.

Ps. is there a shift from warding off periodontitis in the premise to eliminating periodontitis in the conclusion??

[okjoannawow]

Do you think that generally, it's a good rule of thumb to eliminate answers like A unless explicitly stated in the stim? For example, if the researcher was convinced that the ONLY way to prevent gum diseases is to restore cathepsin C to normal levels.

[Brook Miscoski]

okjoannawow,

Keep in mind that the answer to an assumption question will not be stated in the stimulus (because it is assumed). With that in mind, the remainder of what you say is accurate. The stimulus conclusion (last sentence) says that restoring the enzyme makes it possible to eliminate periodontitis, not that it's the only way to do so. So whether a logic word like "only" fits with the stimulus is something you should always consider.

[menkenj]

I still do not understand why A) is incorrect.

Given that this is a CE relationship, I wrote:

Restore CC to normal levels eliminate gum disease

According to the LR Bible, in a CE relationship, the author assumes that the cause is the ONLY thing that leads to the effect and the cause will ALWAYS lead to the effect.

So, doesn't this mean that the researchers assume that restoring CC to normal levels is the ONLY way to eliminate gum disease (A).

Can someone please explain? Thanks!

The 'only way' necessary indicator is a tricky one. The 'way' it's referring to is the restoring of CC levels to normal so that is the necessary condition. So you would diagram (A) as Elimination Periodontitis Restore CC to Normal Levels.
In this way it's a mistaken reversal of the indicated relationship so that's why (A) is wrong.

[Adam Tyson]

Good analysis, menkenj! That's a fine way to eliminate answer A.