LSAT LOGICAL REASONING BIBLE P.253 (JUSTIFY QUESTION)

[salty]

Hi,

I worked out justify question problem set on pg.253 of L.R Bible, and I just couldnt figure, for Q4, why the answer choice 'D' is mistaken reversal of the answer 'A'. Is it because 'Only people who' is same as 'only if', making 'only people who feel secure' a necessary condition and 'know for certain whether their actions are legal' a sufficient condition?

Thank you for your help in advance.

[Nikki Siclunov]

Hi,

Thanks for your question.

Answer choice (A) can be diagrammed as follows:

Feel secure Know actions are legal

The second part of the sentence is a necessary condition, as indicated by "only if" - a necessary condition indicator. Answer choice (A) therefore connects the premises to the conclusion in a way that justifies the latter.

By contrast, in answer choice (D) the second part of the sentence is the sufficient condition, modified by "if" (a sufficient condition indicator):

Laws NOT vague Feel secure

While this is not a Mistaken Reversal of answer choice (A) - not sure why you thought that - it contains an element common to both the premises and the conclusion (vague laws). This makes it unlikely that (D) would help to justify the conclusion, and indeed - the conditional link it presents leads nowhere.

Answer choice (E) is the Mistaken Reversal of (A). "Only people who..." is a necessary condition indicator, similar to "only if." Thus, we can diagram answer choice (E) as follows:

Know actions are legal Feel secure

Does that make sense? Let me know!

Thanks!

[avengingangel]

This question will haunt me in my dreams -- I'm really struggling with the explanation provided in the book.

I chose answer (E) - after I changed my answer from (A) for the third or fourth time - because, to me, it matched logically with the contrapositive of what would be the correct answer. But before I even dig in to that... I was extremely confused by the explanation in the book, because it says that (E) is Mistaken Negation of the correct answer... which I totally threw a fit over.

But your explanation of (D) in this thread makes sense. (D) as incorrect because it's a Mistaken REVERSAL of (A).. as opposed to Mistaken Negation, like the book says! Is this a typo in the book??

I still have 2 remaining questions about this question/the book's explanation, but I need this post answered before I can move on & pose those questions... I've spent over an hour on this 1 question!! I'm going to sleep!

I look forward to a response. Thanks!!

[Nikki Siclunov]

Hi avengingangel,

Thanks for your question. Spending an hour on a single problem is not advisable, and I'm afraid you'll burn out at this rate. Take a step back, and consider this argument structurally. If you understand conditional reasoning, the correct answer choice shouldn't be terribly difficult to figure out.

The argument is structured as follows:

• Premise: Vague laws NOT certain
  
  Conclusion: Vague laws NOT secure

To justify the conclusion, we need to establish the following link:

• Justify: NOT certain NOT secure.

In other words, if someone isn't certain that their actions are legal, then they wouldn't feel secure. The contrapositive of that idea also works: if some does feel secure, then they must know for certain whether their actions are legal (Secure Certain).

Answer choice (A): Secure Certain This is the contrapositive of our prephrase, and is therefore correct.
Answer choice (B): The word "might" is sufficient to throw this out of consideration.
Answer choice (C): Certain Secure. Mistaken Reversal of the correct answer.
Answer choice (D): Laws NOT vague Secure. This leads nowhere.
Answer choice (E): Certain Secure. This is a Mistaken Reversal of answer choice (A). Since answer choice (A) is the contrapositive of our prephrase, we can also think of answer choice (E) as the Mistaken Negation of our prephrase.

Note that the Mistaken Negation and the Mistaken Reversal are contrapositives of each other! It's really the same error in reasoning said in two different ways. The MR confuses a necessary condition for a sufficient one. The MN confuses a sufficient condition for a necessary one. Whether you conceptualize the error in answer choice (E) as the MN or the MR of the missing link does not matter: both are correct, depending on whether you prephrased the positive or the contrapositive form of that link.

Hope this helps! Try to relax!!