Predicate Representation

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Sloth Hero
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Joined: Sun Apr 17, 2011 2:32 pm

Predicate Representation

Postby Sloth Hero » Mon Apr 18, 2011 10:17 am

Has anyone tried, and been able to measure the success of using Universal/Existential quantifiers for rule representation?

It would be for non-linear games most likely. Maybe a few advanced linears.

Like: (∃x)(1x) which would translate to "there exists an x such that x bears relation to 1"
-This would be derived from a rule that states: At least one variable has property "1"

and (∀x)(4g ⊃ 2x) which would translate to "for all x, if g bears relation to 4, then x bears relation to 2

But the more I look at it, formal logic doesn't seem to be as time-efficient for the LSAT.

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suspicious android
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Re: Predicate Representation

Postby suspicious android » Mon Apr 18, 2011 1:17 pm

This is why taking logic classes doesn't really help that much on the LSAT, you tend to overthink things. Everything that's useful on the LSAT they teach in logic classes on the first day of class.

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AntipodeanPhil
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Re: Predicate Representation

Postby AntipodeanPhil » Wed Apr 20, 2011 12:24 am

Yeah, I use some tricks from formal logic - like 'v' for 'or,' an upside down 'v' for 'and,' and '~' for negation, but using quantifiers, scope brackets, and the like is going too far.

IMO, taking logic classes is valuable not for the information learnt, which might get in the way - as above - but for the skills. I would suggest taking a logic class a year or two before the LSAT, since you will likely retain the skills but lose the information. The skills - expecially those required for complicated deductions - fit fairly closely with the skills required for LGs, in my view.

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Sloth Hero
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Re: Predicate Representation

Postby Sloth Hero » Wed Apr 20, 2011 11:03 am

Yeah antipodean is right.

LSAT doesn't require 30 line derivations unlike the exam I took for PD+ earlier today did. :|

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AntipodeanPhil
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Re: Predicate Representation

Postby AntipodeanPhil » Wed Apr 20, 2011 11:25 am

Sloth Hero wrote:LSAT doesn't require 30 line derivations unlike the exam I took for PD+ earlier today did. :|

LOL. Yeah, proving soundness and completeness in secord-order logic makes the LSAT look like child's play.

Thinking about logic and the stuff we were talking about on the other post gave me an idea for a new LG question type. They could give you a setup with various conditions that would together be inconsistent, and then ask you which condition, if dropped, would make the others consistent - like a reductio. Easy questions you could answer just by looking at the conditions; harder questions would require hypotheticals.

They advertise for new test-making staff every year - perhaps this is my way in!

FloridaCoastalorbust
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Joined: Mon Feb 21, 2011 4:43 pm

Re: Predicate Representation

Postby FloridaCoastalorbust » Wed Apr 20, 2011 11:39 am

Universal and existential quantifiers IMO are pointless. Many statements could be represented with the univ. and a few with existen., but that really won't help you out. I agree with above that some symbols can be helpful such as the negation, wedge (disjunctive), and ampersand (conjunctive). The ability to construct complex proofs using a shitload of rules (think existential generalization, universal instantiation, DeMorgan's, Hypo syllogism, etc.) will give you an edge when starting to PT, I feel




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