#14 - Expert: What criteria distinguish addictive substances

[ege222]

Once again, I had completely ruled out C, which turned out to be the correct answer. I felt good about my chosen answer A. Why is C the correct answer and why is A incorrect?

Thanks in advance,
Elizabeth

[Lucas Moreau]

Hello, Elizabeth,

A is incorrect because of how the question is set up. The conclusion in the stimulus says that a substance should be considered addictive if most habitual users of it suffer extreme difficulty when ceasing to use. A stands for the proposition that a substance should be considered addictive if some, or even one habitual user of it suffers extreme difficulty when ceasing to use. A goes too far!

As for C, it's saying that a substance is only addictive if most habitual users cannot cease to use with little difficulty - in other words, it's addictive if most habitual users suffer extreme difficulty when ceasing to use. C is a convoluted way of restating the conclusion, and so it is the correct answer choice.

Hope that helps,
Lucas Moreau

[Jkjones3789]

So I attempted to look at the other explanations to see if I could understand. In this question I chose D. Why is it C?

[KelseyWoods]

Hi Jkjones!

I'm guessing you liked answer choice (D) because it seems like a contrapositive of that last sentence. But notice that in the last sentence, the necessary condition for a substance to be classified as addictive is that withdrawal from habitual use causes most users extreme difficulty. Answer choice (D) is talking about only one person, not most people and it doesn't mention anything about withdrawal, so it isn't a contrapositive and isn't something that must be true based on the information we have. Just because one habitual user of the substance doesn't experience any difficulty from using it doesn't mean that most habitual users of the substance won't experience difficulty if they try to stop using it.

So let's look at why answer choice (C) is correct. Answer choice (C) goes back to that conditional criteria the author gives us for determining if a substance is addictive. To be addictive, it is necessary that the withdrawal from habitual use causes most users extreme difficulty. So if there is a substance that some habitual users can stop taking without extreme difficulty, then that substance will only be considered if what is true of some is not true of most. In other words, as long as most users are still experiencing extreme withdrawal, the substance would be addictive whether or not there are some users who are not experiencing extreme withdrawal.

Hope that helps!

Best,
Kelsey

[olafimihan.k]

Would answer choice A be considered a mistaken reversal?

[Eric Ockert]

It is close to being a Mistaken Reversal. For practical purposes, you are essentially right.

The true Mistaken Reversal would read:

"If withdrawal from a substance causes most users extreme psychological and physiological difficulty, then it is addictive."

Answer choice (A) talks about a user rather than most users. But, answer choice (A) is really flawed for that same reason. The psychological and physical difficulty is a requirement for an addictive substance in the rule in the stimulus. It is not sufficient to prove that a substance is addictive.

Hope that helps!

[LSAT2018]

Given the conditional in the stimulus: Addictive → Cause Most Users Psychological Difficulty

How would the answer be diagrammed?

[Adam Tyson]

Believe it or not...the same way! This answer is not a contrapositive, as we usually get from Must Be True questions with conditional reasoning, but the less commonly seen Restatement form. That is where the author says that the sufficient condition occurs and therefore the necessary condition occurs. This answer is saying a substance is addictive "only if" most users cannot quit is without experiencing those problems. Dealing with the double-negative in the necessary condition - cannot/without - is the toughest part of that answer choice, but once you turn that into a positive, you get something like "most users have those problems." The diagram is then:

Addictive Cause Most Users Psychological Difficulty

That's the original rule from the stimulus, and so it must be true. Boom!