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#72937
Complete Question Explanation

Strengthen-Principle. The correct answer choice is (E).

We are presented with a conditional Principle (note the use of the phrase "only if" in the rule), and an application of that rule. The principle can be diagrammed as follows:

BEA (Buy Expensive Antique) :arrow: CA (Confident of Authenticity) AND FPDIQ (Find Piece Desirable for Intrinsic Qualities)

In the application of the principle, we are told that Matilde should NOT buy the expensive antique, or:

BEAMatilde

In order to strengthen the application of the principle (and be aware that this is a Strengthen, not a Justify question, because the word "justify" in the stem is preceded by the qualifying phrase "most helps"), where the author has concluded that the Sufficient Condition should not occur, we want an answer that shows that a Necessary Condition may not have occurred. In this case, since there are two necessary conditions (CA AND FPDIQ), we need only show that one of those two may not have occurred. It will suffice to show that either Matilde cannot be confident in the authenticity of the piece, or that she does not find it desirable for its intrinsic qualities.

Answer choice (A): This answer indicates that Matilde might be confident about the authenticity of the piece due to her expertise. That's the opposite of what we were looking for, and is therefore a loser.

Answer choice (B): This answer suggests that Matilde is interested in the piece at least partially due to its value as an investment, but that does not mean that she does not also find it desirable for its intrinsic qualities. There is also nothing in this answer to suggest that she cannot be confident in its authenticity. The necessary conditions have not been questioned, so this does nothing to support the conclusion.

Answer choice (C): This answer indicates that Matilde does find the piece desirable for its intrinsic qualities, and it tells us nothing about her confidence in its authenticity, but only that the seller is willing to provide some evidence of that.

Answer choice (D): Don't read too much into this answer! Just because Matilde thinks the piece is under-priced does NOT mean that she is unsure about its authenticity. She might be confident, and very excited about the bargain she is about to get on something she finds desirable for its intrinsic qualities!

Answer choice (E): This is the correct answer choice. This answer indicates that although Matilde does find the piece desirable for its intrinsic qualities, she cannot be confident in its authenticity. That triggers the contrapositive and strengthens (and does so enough to justify) the conclusion that she should not buy the piece.
 fersian
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#64868
Hello. I noticed that this question hasn't been posted, but it is leaving me stumped.

CA - confident of its authenticity
FPDIQ - find the piece desirable for its intrinsic qualities
VI - value as an investment

I diagrammed the principle as: CA & FPDIQ & ~VI --> BEA
Contrapositive: ~BEA --> ~CA or ~FPDIQ or VI

Essentially, in order for the sufficient to work, we need one of the necessary conditions to trigger.
In answer choice 'C', which was what I selected, "suspects that it will be highly desirable to other collectors in the future" triggers the last necessary condition (VI).

Can someone help me as to where I went wrong? I did keep the credited response 'E' as my other contender.

Thank you.
 Adam Tyson
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#64887
You've made a mistaken reversal in your diagram, fersian - the key is the phrase "only if" in the stimulus, which indicates a necessary condition rather than a sufficient one. You spoke about the necessary conditions triggering the sufficient, but it's the other way around - a necessary condition doesn't trigger anything, but is itself triggered by (required by) the sufficient condition. The correct diagram should be:

BEA :arrow: CA & FPDIQ

(the bit about value as an investment is not part of the conditional relationship, as the author is saying that the buyer should want it for more than just that. It's okay if they want it for its value as an investment, but they have to also find it intrinsically desirable.)

The author has concluded that Matilde should NOT buy the antique. That means we need to prove that the sufficient condition does not occur, and to prove that we use the contrapositive and look for an answer where at least some part of the necessary condition fails to occur. Answer E tells us that the authenticity cannot be confirmed (CA), and that's all we need!

As to answer C, it makes no difference whether Matilde is interested in the value of the antique as an investment. What matters is whether that is the ONLY thing she cares about, or if she also desires it for its intrinsic qualities. That answer tells us that she admires its shape and color, so that condition is met, and the contrapositive is NOT triggered by this information.

Use that "only if" as your guide to set up the diagram, and you'll be good to go!
 fersian
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#64935
Hi Adam,
Thank you very much for your explanation. It was very helpful!

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