Conditional & its Contrapositive in Limited Options?!?

MissLucky
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Conditional & its Contrapositive in Limited Options?!?

Postby MissLucky » Tue Sep 28, 2010 1:07 pm

Okay, so the LSAT Blog's explanation for Game 2 of PT60 sets up limited options based on the rule If M is before P, then H is before G. It makes 2 diagrams:

"One with the conditional rule of: M before P ---> H before G
Another with its contrapositive: G before H ---> P before M"

However, when I tried to set up limited options in PT52 game 4 based on this same idea - creating two main diagrams, one of the conditional in rule 3 and one of its contrapositive (even though the last rule was the basis for a much clearer [and the valid] limited options), this gave me more than one feasible answer for question 19 and question 20's "must be true" questions.

Rule 3 was: F...M ---> L...H
H....L ---> M...F

So I made one diagram with F before M and another with H before L.

Before reading the explanation to game 2 in the LSAT blog, I would have never created limited options based off of a conditional and its contrapositive (just when thinking about it intuitively, it does not make sense because those aren't the only 2 possibilities...L could come before H in other situations that don't have F before M, etc.) but I can't articulate neatly why to myself - can someone actually explain why not?

And why was it okay to do so in the LSAT Blog for game 2 (or was that not okay)? Here is a link to that: http://lsatblog.blogspot.com/2010/07/ls ... ptest.html

thanks a lot!

JJDancer
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Re: Conditional & its Contrapositive in Limited Options?!?

Postby JJDancer » Wed Sep 29, 2010 8:12 pm

I'll comment on PT 60.

M..P --> H..G
The inference I made here was that this means that J = 6 (last)
-H..G --> - M..P
which in THIS CASE = [G .. H --> P..M]

I did not create 2 different templates for this.
I had one main template that had L/M/P/G in 1
and J/H as last (except if M..P --> H..G (J=6)]

My not rules were: no J or H in 1. Latest L can go is 4.

Q 7 I just eliminated whichever ones violated anything.
Q 8. Answered by my not rule.
Q 9. answered by template
Q 10. I wrote out 2 hypos where J came before M (meaning H is last)
LPJGMH and LPJMGH.
I crossed out answer choices B, C, D, E since H was not last in them.
Checked A - GLPJMH works!

Q. 11 Just created hypos with Lright before G (making sure not to violate the M..P/P..M clauses) Considered answers C, D, E.
PLGMJH made D incorrect.
LGPMHJ made E incorrect.

It seems that G has to come before H in this case.. so P..M

Try to put L in 4th (which is what my template/not rules told me was the latest position)
then you would have to fit G, J, and H after it. (meaning 5, 6, 7, -- there are only 6 spots).

Q. 12: Created hypo w M in first. MLHGPJ
This makes A and E incorrect.
Looked at M..P --> H..G (j=6) to see that C is the answer.

hope that helps. Sorry if it's not what you were looking for.

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LSAT Blog
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Re: Conditional & its Contrapositive in Limited Options?!?

Postby LSAT Blog » Thu Sep 30, 2010 12:56 pm

The diagramming of the conditional and its contrapositive is just fleshing out what happens when the sufficient of either occurs.

However, those are not the only two possibilities for the game, so I wouldn't use the phrase "limited options" to describe this technique.

In my step-by-step approach to the game's questions, I find that some questions allow us to use one of these two more fleshed-out diagrams. However, others require the use of the original diagram, which is simply the connection of the game's 1st and 2nd rules. In these cases, the question stem hasn't necessarily activated the conditional or its contrapositive.

Does this clear it up?

MissLucky
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Re: Conditional & its Contrapositive in Limited Options?!?

Postby MissLucky » Thu Sep 30, 2010 8:42 pm

ahhh - i see. makes perfect sense now. thanks for the clarification and for all the other help!

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Re: Conditional & its Contrapositive in Limited Options?!?

Postby LSAT Blog » Sat Oct 02, 2010 1:01 pm

Glad it makes sense now! Please let me know if you'd like me to elaborate on any of my other LG explanations.




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