Logical reasoning PrepTest 136 · Section 2 · Question 5

Incorrect. Whether or not the disease it causes can be treated doesn't define whether something should or should not be considered a commensal, according to the provided definition. Additionally, to undermine this argument, we want to find a difference between the two bacteria since the author relies on them being similar.

Incorrect. The author relies on the likelihood of getting a disease from a bacteria to establish the connection, not the length of the disease.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Commensal - A beneficial bacteria
H. pylori - Strengthens immune response; causes ulcers in >10% of people with it
Many scientists - H. pylori is a commensal
Rebuttal - M. tuberculosis causes tuberculosis in >10% of people, but no one would call it a commensal
Conclusion - The scientists are "misguided"

Answer Anticipation:
Without a doubt, the LSAT is trying to get you wrapped up in those long, Latin names so that you miss the logic and get confused by the science. Don't fall for it!

If the LSAT wants you to know something about science, it will tell you. And here, it tells you up front what a commensal is—it's a bacteria that can benefit humans. The argument then jumps into what "many scientists" are considering an example of a commensal—H. pylori, despite it causing ulcers in some people, because it strengthens immune response.

To rebut this classification, the author brings up a comparative/analogous situation. This other bacteria is one that causes tuberculosis in about the same percentage of people that H. pylori causes ulcers. So there is a similarity there. However, there's also a difference—H. pylori is established as benefiting people, whereas M. tuberculosis isn't. This is key because the definition of "commensal" involves the beneficial impact of the bacteria!

The author of this argument fails to establish this relevant similarity in the analogous bacteria—that it, too, provides a benefit. Without establishing that, the rebuttal fails, so let's look for an answer stating that M. tuberculosis doesn't provide any known benefits to people who are infected with it.

Answer Explanation:
This answer choice highlights a relevant difference between the two bacteria, thus undercutting the author's use of M. tuberculosis as a rebuttal. Since the argument is about whether H. pylori should be considered a commensal, and commensals are beneficial bacteria, whether or not M. tuberculosis provides a benefit is key to the argument. By stating that it doesn't, this answer successfully weakens the author's argument.

Key Takeaway:
First, the LSAT only expects you to know science that it explains to you, so don't get wrapped up in the science but pay attention to anything that the LSAT defines. Second, when two situations are compared, line up the points of comparison to see if any are missing.

Incorrect. The number of people who are infected with a bacteria doesn't play a role in whether it's a commensal or not. This answer is trying to get you to bite on something to do with that 10% rate, but don't bite! We know that percentages and numbers are different considerations.

Incorrect. The number of people who are infected with a bacteria doesn't play a role in whether it's a commensal or not. This answer is trying to get you to bite on something to do with that 10% rate, but don't bite! We know that percentages and numbers are different considerations.