Reply To: Assumption (Nec) questions PT 63 VERSUS PT 64

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.