PT 69, S4 Q6; negative conditional reasoning?

drumstickies
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PT 69, S4 Q6; negative conditional reasoning?

Postby drumstickies » Wed Sep 18, 2013 10:49 am

I thought I understood conditional reasoning pretty well until I got this question wrong.

It says something along the lines of "unless he or she in an accountant or his or her membership is unanimously supported, he or she cannot be on the finance committee."

So, when I diagrammed it, it was--

~accountant OR ~unanimous --> ~finance committee

Since OR in the sufficient means that either will trigger the necessary, I thought A was correct. I got it wrong. Does the OR rule change when the sufficient conditions are negated?

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ScottRiqui
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Re: PT 69, S4 Q6; negative conditional reasoning?

Postby ScottRiqui » Wed Sep 18, 2013 11:38 am

drumstickies wrote:I thought I understood conditional reasoning pretty well until I got this question wrong.

It says something along the lines of "unless he or she in an accountant or his or her membership is unanimously supported, he or she cannot be on the finance committee."

So, when I diagrammed it, it was--

~accountant OR ~unanimous --> ~finance committee

Since OR in the sufficient means that either will trigger the necessary, I thought A was correct. I got it wrong. Does the OR rule change when the sufficient conditions are negated?


Your diagram should have been:

~accountant AND ~unanimous --> ~finance committee

If she is on the finance committee, then either she's an accountant, or her membership was supported unanimously:

finance committee --> accountant OR unanimous

Taking the contrapositive (using DeMorgan's Rule), we get

~accountant AND ~unanimous --> ~finance committee

drumstickies
Posts: 78
Joined: Wed Aug 12, 2009 7:53 pm

Re: PT 69, S4 Q6; negative conditional reasoning?

Postby drumstickies » Wed Sep 18, 2013 11:47 am

Thanks for the response. You're absolutely right. I do want to push back, though, in order to correct my misunderstanding.

MLSAT says that "unless" and "except perhaps" should be diagrammed as "if not" (page 347). So, using MLSAT's strategy, shouldn't it have been diagrammed ~accountant OR ~unanimous --> ~finance committee?

How do you normally diagram "unless"?

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ScottRiqui
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Re: PT 69, S4 Q6; negative conditional reasoning?

Postby ScottRiqui » Wed Sep 18, 2013 11:53 am

drumstickies wrote:Thanks for the response. You're absolutely right. I do want to push back, though, in order to correct my misunderstanding.

MLSAT says that "unless" and "except perhaps" should be diagrammed as "if not" (page 347). So, using MLSAT's strategy, shouldn't it have been diagrammed ~accountant OR ~unanimous --> ~finance committee?

How do you normally diagram "unless"?



I generally just "plain English / common sense" it. If a statement says "no one is happy unless they're healthy", then the consequence is that if someone is happy, they could only get that way by being healthy:

happy --> healthy

I guess if you want a formal rule, it would be " The term 'unless' introduces a necessary condition."

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sashafierce
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Re: PT 69, S4 Q6; negative conditional reasoning?

Postby sashafierce » Wed Sep 18, 2013 12:16 pm

ScottRiqui wrote:
drumstickies wrote:Thanks for the response. You're absolutely right. I do want to push back, though, in order to correct my misunderstanding.

MLSAT says that "unless" and "except perhaps" should be diagrammed as "if not" (page 347). So, using MLSAT's strategy, shouldn't it have been diagrammed ~accountant OR ~unanimous --> ~finance committee?

How do you normally diagram "unless"?



I generally just "plain English / common sense" it. If a statement says "no one is happy unless they're healthy", then the consequence is that if someone is happy, they could only get that way by being healthy:

happy --> healthy

I guess if you want a formal rule, it would be " The term 'unless' introduces a necessary condition."


And then you make the other part of the statement the sufficient condition and negate it.

Steve from the LSAT blog explains both method really well:

http://lsatblog.blogspot.com/2009/11/wo ... -mean.html




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