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Logical Reasoning Bible 2019 edition Chapter 6 pp. 206-207

LSATstudent2019
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Hello,

I'm two weeks into LSAT prep and have a question on a specific practice problem on the Earth's axis on page 206-207 in Chapter 6. It is a conditional linkage question and I am having issues grasping the diagramming.

In this question "only" and "without" are the key indicator words ( the word "without" invoking the unless equation)

AS=angle stable
GI=gravitational influence of Earth's large, nearby moon.
PCE= planet's climate too extreme and unstable to support life

Its diagrammed this way:

AS :arrow: GI
PCE (w/strike through it) :arrow: AS

I understand up until this point... but figuring out the sequence of the chain in this example is what I find tricky...
In the book the chain is: PCE (w/strike through it) :arrow: AS :arrow: GI

But how do we know the chain couldn't also have been written out as: GI :arrow: AS :arrow: PCE (w/strike through it)

In other words, how do I figure out the order its suppose to go in?
Dave Killoran
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Hi LSATstudent,

Thanks for the question! This is a tricky set of statements, and thus this question has come up before. For starters and for anyone else, please check out the following two discussions:



Now, in reference to your specific question, the chain can be configured in either of two ways:


    PCE :arrow: AS :arrow: GI

    OR, the contrapositive of the above:

    GI :arrow: AS :arrow: PCE

As mentioned earlier in the book, a statement and its contrapositive are functionally identical, and you want to reach a point where you mentally see both statements at once, so once we have a statement we often don't write down the CP separately. Thus, you could have written either one down and it would be just fine :-D The reason we did it as in the book as that we can link both statements through AS with no further manipulation. To make the other chain in requires taking CPs to make it.

Please let me know if that helps. Thanks!
Dave Killoran
PowerScore Test Preparation

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