Sufficient & Necessary condition

[Germin Lim]

Hi, I'd like to ask a question about conditional reasoning which I encountered on a non-english website, the question is roughly translated into:

If students apply, they will obtain the promotion.
If the above statement is true, which of the following statements is also true?
A If a student applies, the student will achieve the best result.
B Students will be promoted only those students who applied.
C If a student does not apply, the student will be rejected.
D If a student has been promoted it is possible that the student has applied.
E Being promoted is difficult.

I diagrammed the stimulus as:
A -> P
I was indecisive between B & D because they can both be diagrammed as:
P -> A
The correct answer is D. The stimulus seems to have a mistaken reversal of the correct answer, or the other way around. what makes answer B wrong and D correct?

[Adam Tyson]

Tough question, Germin, and one I am hesitant to answer because of the translation issue. Was this from a real LSAT, or was it created by someone to resemble an LSAT question? PowerScore materials only use real, licensed questions, and we encourage our students to only study those real ones (along with drills that use the same reasoning, but without the details of a stimulus). "Simulated" LSAT questions are often more trouble than help because they are not as rigorously created and vetted as the real ones, and they end up causing confusion and frustration.

That said, I am going to take a stab at this one, with some modification.

First, I think your diagram of the stimulus is probably correct, assuming nothing got too badly scrambled in translation. I think they are saying that if you apply, you get promoted, or A -> P. Now answer B is a bit of a mess, probably due to translation issues, so I am going to rewrite it. I think answer B probably ought to say "Students are promoted only if they apply", and that would diagram as P -> A. That is a classic Mistaken Reversal - the Necessary Condition never guarantees the Sufficient Condition. Applying guarantees promotion, according to the stimulus, but it may not be the only way to get promoted. Maybe just doing a good job, or smiling at the boss, or getting compliments from customers, could also be sufficient for a promotion?

Answer D is saying that if the Necessary condition occurs, the Sufficient COULD occur, and that is absolutely correct. While the presence of the Necessary doesn't PROVE that the Sufficient occurs, it does ALLOW the Sufficient to occur. Being promoted means it is possible that you applied, although it may not be required. That's not a mistake, and it's not even a contra-positive, it's just a recognition of the nature of conditional reasoning - when the Necessary condition is present/occurs, it opens the door to the possibility of the Sufficient being present/occurring.

The key language that makes D good and B bad is that D doesn't require anything to happen, but says only that it is possible.

I hope that clears things up! Now, stay away from any unofficial, simulated LSAT questions - there is enough licensed, official stuff available, through PowerScore and elsewhere, that you should never need to mess around with inferior products. When you have the best, who needs the rest?

[Germin Lim]

Thanks a million Adam, This helps a lot!
Actually, this is not a question meant for LSAT, and to be honest I'm not preparing for the LSAT but rather I'm using powerscore logical reasoning bible to prepare for my exam which contain questions that are very similar to the logical reasoning questions appear in the LSAT. Powerscore's information has been very useful and so does your explanation, thank you!