A common genetic mutation that lowers levels of the enzyme cathepsin C severely reduces a person's ability to ward of...

Naz on July 23, 2015

Here we have a strengthen with necessary premise question. Remember that a premise is necessary for a conclusion if the falsity of the premise guarantees or brings about the falsity of the conclusion. First we check to see if the answer choice strengthens the passage, and then, if it does strengthen, we negate the answer choice to see if its negation makes the argument fall apart. If the answer choice does both those things then it is our correct answer.

Conclusion: Once researchers develop a way to restore the enzyme to normal levels, we will be able to eliminate periodontitis.

Why? We know that the enzyme cathepsin C destroys diseased cels and eliminates infections. However, a common genetic mutation that lowers levels of the enzyme cathepsin C severely reduces a person's ability to ward off periodontitis.

What's the issue here? The enzyme helps ward off periodontitis. Have we been given any information on whether the enzyme prevents periodontitis, as well? No.

Does answer choice (A) strengthen? No.

Whether or not restoring the enzyme to normal levels is THE ONLY WAY to eliminate periodontitis does nothing to our argument. We need to know whether when enzyme C levels are restored to normal in a person, they will no longer get periodontitis.

Does answer choice (D) strengthen? Yes.

(D) is explicitly telling us that someone whose enzyme levels are restored to normal will not suffer from periodontitis, i.e. periodontitis will be prevented.

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

Does the negation make the argument fall apart? Yes.

If someone whose enzyme levels have been restored to normal levels can still get periodontitis, then it no longer stands that bringing the enzyme levels up back to normal will eliminate periodontitis.

Hope that helps! Please let us know if you have any other questions.

djayasinghe on August 28, 2018

Do you mean E instead of D is the correct answer?

Sheza on August 2, 2020

Hi @Naz I'm not sure I understand the explanation fully. If the conclusion is calling to "eliminate periodontitis" shouldn't the answer choice contain an assumption that addresses this point of elimination? I'm not sure how E does that, although I follow the negation explanation.
Could you please show how the test to first see if it strengthens the passage and then negating the answer choice to see if it makes the argument fall apart doesn't hold for choice A? Wouldn't a negation (restoring the enzyme to normal levels is not the only way to eliminate periodontitis) also make the argument fall apart?
Thank you

shunhe on August 4, 2020

Hey everyone,

Thanks for the question! So first, to clear up any possible confusion, (E) is the correct answer and not (D).

Now as to applying the test to (A): let’s take the negation of (A). So (A) tells us that restoring cathepsin C to normal levels is the only way to eliminate periodontitis. And the negation of this would be that restoring cache-sin C to normal levels isn’t the only way to eliminate periodontitis; in other words, there are other ways out there to eliminate periodontitis. Does this break the argument? The argument here is that if researchers do this thing X, we can eliminate periodontitis. Does the fact that we can also do Y and Z to eliminate periodontitis damage that argument? No, not really. There can be multiple ways to eliminate periodontitis, all of which exist mutually. So the negation of (A) doesn’t really damage the argument, and so (A) can’t be the necessary assumption.

(E) does help show that periodontitis will be eliminated, since the argument’s assuming that a person whose cathepsin C level has been restored to normal won’t suffer from periodontitis. If it couldn’t assume that, then we couldn’t say that we’ll eliminate periodontitis. That’s what allows us to bridge the idea of eliminating periodontitis with

Hope this helps! Feel free to ask any other questions that you might have.

Sheza on August 12, 2020

Thanks very much @Shunhe