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I have taken the question and my approach to it from the following discussion http://www.beatthegmat.com/just-saw-this-cr-on-btg-which-seems-weird-experts-help-t70756.html#319881. The entire discussion might not be relevant to everyone so I just brought out the question and my explanation here.

Source: (Was posted in the discussion above as from 300 GMAT CR) is actually December 1994 LSAT test from the first Logical Reasoning section, it was question 10 on that test. (Fun fact...this was my LSAT test, as in I took this Dec 1994 test on the way to Law School).

Here is the question:

"10. Every political philosopher of the early twentieth century who was either a socialist or a communist was influenced by Rosa Luxemburg. No one who was influenced by Rosa Luxemburg advocated a totalitarian state.

If the statements above are true, which one of the following must on the basis of them also is true?

(A) No early-twentieth-century socialist political philosopher advocated a totalitarian state.

(B) Every early-twentieth-century political philosopher who did not advocate a totalitarian state was influenced by Rosa Luxemburg.

(C) Rosa Luxemburg was the only person to influence every early-twentieth-century political philosopher who was either socialist or communist.

(D) Every early-twentieth-century political philosopher who was influenced by Rosa Luxemburg and was not a socialist was a communist.

(E) Every early-twentieth-century political philosopher who did not advocate a totalitarian state was either socialist or communist. "


Here is my analysis:

This question is taught in LSAT classes as a perfect example of FORMAL LOGIC which means that it is very valuable to the LSAT, but may be a little tricky for GMAT studying.

With that said, I think that we can approach this one with our Must be True tools in hand.

HOW TO APPROACH AN INFERENCE/ CONCLUSION QUESTION

Remember that for a Must Be True question you are looking to eliminate the four answer choices that Could Be False. Could be True means nothing - anything could be true. I could actually be a computer that was designed to answer BTG questions and not a person at all. So do not think about Could Be True only eliminate those choices that COULD BE FALSE.

There are four ways to recognize those choices that Could Be False:

1) Out of Scope (a good way to find these is to ask yourself “what does the stimulus say about ___?”)

2) Predictions (those things that are in the future are not Must Be True)

3) Must Be False (Some things are actually counter to the facts already stated)

4) Commands (Telling someone what they “should” do is usually not must be true).

Let’s look at this question. The first thing we want to do is understand the scope of the stimulus - what do we know from this stimulus? We know a couple of things we know something about “early-twentieth century socialists and communists” being influenced by Rosa Luxemburg. And we also know about people who do not advocate totalitarianism (those influenced by Rosa Luxemburg).

Things we do not know about? We do not know if anyone actually advocates totalitarianism. We do not know about those who are not early-twentieth century philosophers or those who are not socialists or communists. So if someone was from a different time period or was an advocate of democracy then we cannot say anything about that person - it would be out of scope.

For an inference/conclusion question I do not spend a lot of time with the stimulus - just really understand what the scope is and is not and then move to the answer choices looking to eliminate the 4 that could be false. On your first time through the answer choices it is better to eliminate those that are out of scope and/or predictions first. These are easier to see. If a choice is possibly a command or a must be false come back to those later for intense analysis.

Answer Choice A) This is specific to socialist political philosophers of the early 20th century. (I will give further discussion of this answer choice at the end - for now we would move on and not eliminate this choice because it is not out of scope and not a prediction).

B) ELIMINATE - could be false - out of scope. Remember, we do not know about every early 20th Century philosopher only the socialists, communists and those influenced by Rosa Luxemburg.

C) ELIMINATE - could be false - out of scope. We do not know whether other persons influenced every early 20th Century socialist and communist. It could be that - for example - Karl Marx also influenced each of these people.

D) ELIMINATE - could be false - out of scope. Just because we know that Rosa Luxemburg influenced all of the socialists and communists does not mean that those are the only people she influenced. She could have influenced those who favor democracy or anarchy or some other system.

E) ELIMINATE - could be false - out of scope. This answer choice states that if a political philosopher was not totalitarian that he or she was either a communist or a socialist. This is certainly beyond the scope. It is possible that some people in favor or democracy are not totalitarians.

Returning to Choice A: Here is where the formal logic comes in: if a person is an early 20th Century socialist political philosopher that person is influenced by Rosa Luxemburg and that person is then not an advocate of totalitarianism. This is like the transitive property in math. If A = B and B= C then A = C. This is an example of formal logic and would not be tested in this way on the GMAT. However that does not mean you cannot use some formal logic to help you on the GMAT!

Yet as you can see, even on a question like this, formal logic is not needed as we can eliminate the incorrect and get down to just one answer.

Questions?

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David Newland, JD, MA, MAE
GMAT Instructor, Tutor, and Author
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