Manhattan LSAT RC BOOK q- formal logic

lawschoolplease1
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Joined: Mon Feb 06, 2012 1:56 pm

Manhattan LSAT RC BOOK q- formal logic

Postby lawschoolplease1 » Sat Nov 30, 2013 1:08 pm

I'm hoping someone from Manhattan LSAT can answer this question. I'm looking at page 61. It basically says..."most people prefer X to Y...we can infer: at least some people prefer Y to X." Isn't this against formal logic since most can mean all? Does formal logic not apply to RC?

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Christine (MLSAT)
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Joined: Fri Nov 22, 2013 3:41 pm

Re: Manhattan LSAT RC BOOK q- formal logic

Postby Christine (MLSAT) » Sun Dec 01, 2013 12:56 pm

lawschoolplease1 wrote:I'm hoping someone from Manhattan LSAT can answer this question. I'm looking at page 61. It basically says..."most people prefer X to Y...we can infer: at least some people prefer Y to X." Isn't this against formal logic since most can mean all? Does formal logic not apply to RC?


I answered this in the geek thread, but just in case someone else comes looking for this here, here's my earlier reply:


Excellent catch! This was completely an error!

That issue is on the errata list for the RC book, and will be removed in the next edition of the book.

While it would be quite rare for an RC question to explicitly test this kind of formal logic distinction (they'll save it for LR!), it's absolutely NEVER permissible to infer that 'most' necessarily means 'not all'. As a practical and strategic point, I can't think of an example in RC where this kind of bad inference would lead you directly to a wrong answer, but it's possible, so your guard should always be up.

The fact that you noticed this bodes well for your critical reading skills. :p




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