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sufficient and necessary diagramming drill powerscore q

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sufficient and necessary diagramming drill powerscore q

by shoot4greatness » Tue Aug 09, 2011 5:12 pm
This question pertains to grammar. It is from powerscore cr bible sufficient and necessary diagramming drill

"Maria will not speak during the meeting unless the chairman does not speak."

Grammatically, I have no idea what is happening here. Anyone care to chime in?

Edit: To moderator, would you please move this thread to sc section? Seems like sc section is more befitting section.
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by XLogic » Tue Aug 09, 2011 5:20 pm
shoot4greatness wrote:This question pertains to grammar. It is from powerscore cr bible sufficient and necessary diagramming drill

"Maria will not speak during the meeting unless the chairman does not speak."

Grammatically, I have no idea what is happening here. Anyone care to chime in?
A formula I use often (suggested by experts) is to convert "unless" to "If not"

If so, the statement above becomes:

Maria will not speak during the meeting if not the chairman does not speak.

Sounds awkward but you should get the gist. The above statement can now be written as

If not the chairman does not speak, then Maria will not speak during meeting

Notice the double negative not-not. not cancels out not!

If the chairman speaks, then Maria will not speak during meeting
> Chairman speaks --> Maria not speak
> Maria speaks --> Chairman not speak (contrapositive)

Thoughts??
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by XLogic » Tue Aug 09, 2011 6:03 pm
A formula I use often (suggested by experts) is to convert "unless" to "If not"
I have seen two methods (suggested by experts) to tackle "unless", "except" and "perhaps" key words in CR passages. All three key words are equivalent (or are used in much the same way) in CR passages.

For example: X event will occur UNLESS Y event occurs. This means that the X event will not occur only when Y occurs, otherwise X event will always occur. Which means if X did not occur then we know necessarily that Y occurred.

Method 1: Replace "Unless" with "If Not"

As stated earlier, with this method we replace "unless" with "if not". And we know that "if" introduces the sufficient condition in a "if..then" statement.

E.g. X unless Y = X if not Y
X if not Y is equivalent to if not Y, then X
> not Y --> X
not X --> Y (contrapositive)

Method 2: "Unless" Intros Necessary Condition

With this method, "unless" always introduces the necessary condition, and the other variable is negated to form the sufficient condition.

E.g. X unless Y
Y = necessary condition, not X = sufficient condition
sufficient --> necessary
> not X --> Y
not Y --> X (contrapositive)

Let me know if this makes sense!

Sources: CR Books, and online references...
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by shoot4greatness » Tue Aug 09, 2011 6:27 pm
Thanks X,

I always thought double negatives "cancel" each other out. But, when I was reading the sentence, it drove me nuts trying to juggle with the idea of having three negatives (when I was substituting unless with if not). Well, it does make sense there are three "not" in the sentence. Whether you go from left to right or right to left, the contrapositive deduces same meaning.
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by shoot4greatness » Tue Aug 09, 2011 6:34 pm
Hey X, how about this?

take out the negative from the chairman. then the sentence is

"Maria will not speak during the meeting unless the chairman speaks" ----> If the chairman does not speak, Maria will not speak.
( fairly easy sentence to grasp)

Insert negative back

"Maria will not speak during the meeting unless the chairman does not speak" ----> If the chairman speaks, Maria will not speak

Chairman speaks ---> Maria will not speak
Maria speaks ---> chairman does not speak
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by XLogic » Tue Aug 09, 2011 7:57 pm
shoot4greatness wrote:Hey X, how about this?

take out the negative from the chairman. then the sentence is

"Maria will not speak during the meeting unless the chairman speaks" ----> If the chairman does not speak, Maria will not speak.
( fairly easy sentence to grasp)
Looks good.
shoot4greatness wrote: Insert negative back

"Maria will not speak during the meeting unless the chairman does not speak" ----> If the chairman speaks, Maria will not speak

Chairman speaks ---> Maria will not speak
Maria speaks ---> chairman does not speak
Looks good too :-)
Don't you just love those contrapositives!!
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by mundasingh123 » Wed Aug 10, 2011 2:32 am
This chapter is only relevant to LSAT . Why are we spending so much time on logical reasoning .
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by David@VeritasPrep » Wed Aug 10, 2011 5:14 am
Thanks for that MundaSingh!!!

I was about to say the same thing. No way are you facing this problem on the GMAT. I was just working on this with an LSAT class the other night.

That is the problem with the PowerScore materials -- they are developed for the LSAT.

You can spend way too much time on this.

By the way, if you have to know the easiest way to deal with "unless" is to just be stubborn and logical. No need for double negatives. Example.

"You will not get dessert unless you clean your room." Now be stubborn - no one is going to tell me what to do. So that means you don't clean your room. So what is the result of this? You do not get dessert. Simple, sufficient is don't clean necessary is no dessert. Take the contrapositive, Dessert means you did clean.

But let me state it again, this is not GMAT.

As for sentence correction, main clause "Maria will not speak" modifier "during the meeting" and dependent clause "unless the chairman does not speak." This is an acceptable sentence from a grammatical perspective.
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by XLogic » Wed Aug 10, 2011 9:07 am
This chapter is only relevant to LSAT. Why are we spending so much time on logical reasoning.
I only responded to a question. Some Logical reasoning is tested on the GMAT, but I see your point.

Thanks for that MundaSingh!!!

I was about to say the same thing. No way are you facing this problem on the GMAT. I was just working on this with an LSAT class the other night.
Again, only responded to a question. This stuff is tested on LSAT huh... maybe I'm prepping for that test :-) ... But in all seriousness, I didn't mean to go ultra *logical* in the forums. Y'all are correct, too much formulaic-ness on the GMAT doesn't help (balanced approach is key!).

That is the problem with the PowerScore materials -- they are developed for the LSAT.
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by shoot4greatness » Wed Aug 10, 2011 10:33 am
Thanks X for checking my question out. You never know what type of questions may appear on CR, and powerscore book does state that it is rare. My initial intention for asking the question was in terms of grammatical clarity. However, logical background was necessary for interpretation and X unequivocally provided explanations to my question. Again, thanks X. For those who are flamming this topic, yes I understand it may not be necessary to go over this type, but X and I spent merely 6 posts asking/answering. I don't feel like I've spent too much time, because at the end, I understand the question and my frustration is gone. Case closed.
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