## #5 - When girls are educated in single-sex secondary schools

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Complete Question Explanation

Parallel Flaw-SN. The correct answer choice is (B)

The stimulus of this problem contains a classic Mistaken Reversal error, where the author incorrectly attempts to use the necessary condition of a given relationship to conclude that the sufficient condition must be true. Here is the first sentence premise:

Sufficient Necessary

Educated single-sex school Do better academically

The author then goes on to conclude that, since Alice did better academically than her peers, she was probably educated at a single-sex school. In other words, because the necessary condition has been met, the sufficient must also have occurred.

This is the hallmark of a Mistaken Reversal, where satisfying the condition at the end of the arrow (necessary) is thought to also satisfy the condition at the beginning of the arrow (sufficient). The reason that is flawed is that there could be other reasons besides being educated in a single-sex school that explain Alice's strong academic performance, and therefore we can't know for sure what type of school she previously attended.

(Note the the conditionality here is what I'd call "light" conditional reasoning, as it's qualified ever so slightly with words like "tend to" and "probably;" the principle of an incorrect reversal still holds however, and for ease of diagramming below you'll see me focus on the reversal idea rather than those hedging words)

Answer choice (A): This answer choice is simply a restatement, where the conditional premise is repeated in the conclusion. The first line states that:

Sufficient Necessary

Individual math tutoring Good grades on finals

We're then told that Celia received individual tutoring, so it makes since to conclude that she will probably get good grades. That is valid reasoning, so (A) is out.

Note too that this answer choice deals with the same subject as the stimulus (academics and grads), making it even more unlikely to be correct.

Answer choice (B): This is the correct answer choice. It contains the same reversal error as the stimulus. First sentence:

Sufficient Necessary

Babies taught to swim More ear infections

The author then goes on to conclude that, since Janice has more ear infections than anyone else in the swimming club, she was probably taught to swim as a baby. Note the immediate reversal that has occurred! Of course, as with the stimulus, there could be other reasons besides being taught to swim as a baby as to why she has more ear infections than the other swim club members, so this is a duplicate of the stimulus's flaw.

Answer choice (C): Here we have neither a reversal nor a restatement, but rather the introduction of a new, third term. The author in (C) starts with a conditional form, but then moves from that (study music early appreciate variety) to conclude something about the talent of future musicians. This new term immediately removes this choice from consideration.

Answer choice (D): This answer choice contains flawed reasoning, but the flaw is not quite the same as the one in the stimulus. Instead, this is known as a Mistaken Negation, where the absence of the sufficient condition is used to incorrectly conclude the absence of the necessary. Here's the first sentence:

Sufficient Necessary

Practice piano 30 minutes/day Pass piano exams

Then we're given this fact:

Practice piano 30 minutes/daySally

And finally this conclusion:

Pass piano examsSally

As you can see, this is not the same as the reversal we encountered in the stimulus and in answer choice (B). Instead, the author attempts to apply the original conditional statement despite the fact that the trigger—the initial sufficient condition—never occurs, hence the name Mistaken Negation (the sufficient is gone/negated, and the author mistakenly proceeds anyway). The flaw in this error is that without the sufficient, the necessary is free to occur on not occur: Sally can still pass her exams, even if she practices less than a half hour/day. That amount of practice is enough to guarantee that she will probably pass, but it isn't required to pass.

This flaw and the Mistaken Reversal error are by far the two most errors you will encounter in conditional reasoning on the LSAT.

Answer choice (E): This answer choice has a couple of issues. First, and primarily, it confuses causality with conditionality. We don't know from the stimulus that single-sex schools are the REASON girls tend to do better academically, only that there is a reliable correlation. So saying the first piece causes the second fails to match what we're given in the stimulus. Second, there is no reversal here. We know a reversal must be present, and when one is not the answer is instantly eliminated. Finally, the subject matter of academic achievement makes me nervous: highly unlikely you'd see the same subject as the stimulus repeated in the right answer.
Toby

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Hello!

I mistook the reasoning in this stimulus to be conditional instead of causal reasoning. I saw the "when" in the first sentence and then diagrammed this sentence conditionally. On a similar note, I thought that the reasoning in all of the answer choices was conditional because they all begin with "when." I would really appreciate some tips on differentiating causal from conditional reasoning in questions where conditional indicator words appear. Thanks for help!

Toby
Jon Denning
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Hi Toby - thanks for the message.

I actually agree with you here. To me the hallmark of causality is something actively making a result or outcome occur. I don't see that in this question.

Instead, I see what I'd call light conditional reasoning, where it's not as hardline absolute as you typically encounter ("if...then" style with no qualifying language) due to the presence of the word "tend," but there's still a definitive relationship in place where one term reliably tells you something about the other. And that's more than close enough!

So what I'm going to do here is amend the original explanation up top to correct references to causality to ones about conditionality, and that should do the trick! The upside to that is, aside from calling conditional reasoning causal, the explanation above still works nicely: the diagrams are all accurate, the reversal seen in the stimulus and correct answer are properly noted, and the wrong answers are outlined correctly in terms of how they fail to parallel the original. So at least there's that

Sorry for the confusion and good catch on your end! Changes coming shortly.
Jon Denning
PowerScore Test Preparation

My LSAT Articles: http://blog.powerscore.com/lsat/author/jon-denning
Toby

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Thanks for the clarification, Jon!
EL16

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Hi,

I see the discussion above, suggesting that this is actually conditional reasoning and not causal reasoning. Just to confirm, would this be considered a mistaken reversal?

I had diagrammed it in the following way:
Premise: Girls educated in single-sex school do better academically
Conclusion: Alice does better academically Alice educated in a single-sex school

And then for answer B I diagrammed it as:
Premise: Babies taught to swim more ear infections
Conclusion: Janice has more ear infections Janice taught to swim as a baby

Is this correct, and is the flaw here mistaken reversal?

Thanks!
Elana
Jon Denning
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Elana - that's exactly right! This is a Mistaken Reversal error, both in the stimulus and in the correct answer.

Nicely done!
Jon Denning
PowerScore Test Preparation

My LSAT Articles: http://blog.powerscore.com/lsat/author/jon-denning
TargTru99^
LSAT Apprentice

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Greetings,

I did not realize that the stimulus in this question contained a mistaken reversal, which is why I think I got this question wrong. I interpreted getting "higher grades than any other woman in her first year," a superlative description, as something that was logically different from doing "better academically," a comparative description. How do I avoid making this mistake again?