# Assumption (Nec) questions PT 63 VERSUS PT 64

• May 27, 2016 at 11:14 am #1920
Anonymous
Inactive

Okay so i was comparing the entire set of necessary assumption questions from the both of these tests. I had relatively good success on PT 63, but i struggled a little bit on PT 64. Especially on section 3 #12. I was wondering was there a question similar to the structure that this particular question gave on an older PT that i could look at? Also, in terms of the structure of those necessary assumption questions on PT 64, i was wondering if Mike or anyone else could tell me whether some of these necessary assumption arguments are 1+1=3 type arguments. I’m wondering if that could have contributed to why some of them seem to be a more difficult in comparison to PT 63 where they seemed to be more piece to puzzle fallacies?

• May 27, 2016 at 12:53 pm #1921
LSAT Dan
Participant

The structure on this one is a pretty typical assumption question structure.  It’s that transitive “connected premises” type of argument that occurs more often in sufficient assumption questions, but also quite a bit in necessary assumption questions.  When tracing the structure of these arguments, I find it best to work from the conclusion:

GP –> F

(Garden Path books are flawed.  Some of them, anyway).  The basic structure of the connected premises arguments is this:

A –> B

B –> C

C –> D

A –> D  (conclusion)

Notice that working from the conclusion does two things – it tells you what the starting point of the first (logical first) premise is, and it tells you what the ending point of the last premise is.  So, going back to our conclusion:

GP –> F

The completed argument is going to tell us that some types of books are flawed.  Let’s work backwards; do we have a premise that tells us that certain types of books are flawed?  Yes, books that don’t explain the basics of composting.  So now we’re at:

~EBC –> F

GP –> F  (conclusion)

Continuing to work backward, does that passage tell us that any other types of books don’t explain the basics of composting?  No; that’s a dead end.  So now let’s go to the front of the argument and work forwad.  The conclusion is about books published by Garden Path.  What do we know about those books?  They don’t explain the basics of hot and cold composting:

GP –> ~EDHCC  (Explain the Difference b/tw Hot & Cold Composting)

~EBC –> F

GP –> F    (conclusion)

Do we have a premise about books that don’t explain the difference between hot and cold composting?  No…that’s our second dead end.  So the jump in the argument is between the two premises; we need to link those two to have a completed argument.  It should look like this when it’s all done:

GP –> ~EBHCC

~EDHCC –> ~EBC  (Missing premise; this will be the right answer)

~EBC –> F

GP –> F  (conclusion)

The link we need should be something like, “If a book doesn’t explain the difference between hot and cold composting, then it’s not explaining the basics of composting.”  Or the contrapositive: If a book explains the basics of composting, then it will explain the difference between hot and cold composting.  Since “explaining the difference between hot and cold composting” is on the right side of the arrow when the terms aren’t negated, that’s our necessary term.  That’s answer choice C – to cover the basics, the book MUST explain the difference between hot & cold composting.

Hope this helps.

• May 27, 2016 at 2:54 pm #1922
Anonymous
Inactive

As you pointed out however, we’re use to seeing it on sufficient questions. Was there anything that tipped you off to the structure? I thought that  those connected premise structures were indicated by conditional reasoning??? I only see one conditional statement??

• May 28, 2016 at 7:34 am #1926
Anonymous
Inactive

I see it nevermind

• May 28, 2016 at 8:28 am #1927
LSAT Dan
Participant

I think the best tipoff that that’s the kind of argument structure you’re dealing with is when you see terms repeated, such as “Garden Path” and “flawed” in this one.  Especially coupled with the “if” sentence that we have.  But remember, there are also conditional statements that don’t have “if” triggers, or even “unless” or “only” triggers.  For instance, categorical statements.  “Cats are mammals” is a statement that is logically equivalent to the more obviously conditional, “If an animal is a cat, then it is a mammal.”  As such, “Cats are mammals” (which implies “ALL cats are mammals”) has a contrapositive: Anything that is not a mammal is not a cat.  So there are effectively conditional statements all over the place, including in this particular question.

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