most/some rules help!! :)

nosleeptillsuccess
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most/some rules help!! :)

Postby nosleeptillsuccess » Wed Oct 17, 2012 1:16 pm

Okay let me know if I leave anything out please

1.) Can't get most from a some, can't get some from a most
2.) Can't get a some from a some
3.) Can get a most from a most ONLY when sufficient conditions match

I know I'm missing a few rules...

plz help

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TripTrip
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Re: most/some rules help!! :)

Postby TripTrip » Wed Oct 17, 2012 1:42 pm

You can infer the above as they apply to the same variable.

For example, if you know that "most of the apples are red" you also know that "some of the apples are red."

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arcanecircle
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Re: most/some rules help!! :)

Postby arcanecircle » Wed Oct 17, 2012 1:46 pm

Can't get some from a most


Depends, for example:
All As are Bs + Most As are Cs. You can conclude from this that some Bs are Cs, and also that some Cs are Bs.

Try PT 59-S2-Q19

nosleeptillsuccess
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Re: most/some rules help!! :)

Postby nosleeptillsuccess » Wed Oct 17, 2012 1:52 pm

right got that one...

Um thats pretty much it from what I think right?

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cahwc12
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Re: most/some rules help!! :)

Postby cahwc12 » Wed Oct 17, 2012 2:17 pm

List-form memorization isn't the way you should focus on understanding these concepts. If I tell you that in a group of X, Some A are B, and Some B are C, does it follow that Some A are C? How about Some C are A? How about Some B are A? How about Some C are B? You need to think about these and try to develop a real conceptual understanding here. Give yourself examples and develop your intuition.

Additionally, always try to convert negative information into positive information. If I tell you that you can't do X, Y, and Z, but you know there are only W, X, Y, and Z that you can do, you shouldn't say "can't X, Y or Z" but instead say "can W."

And rule #2 is incorrect/misleading:

Some A are B, Some B are C ---> Some A are C (FALSE)
Some A are B, Some B are C --> Some B are A, Some C are B (TRUE)

You can reverse a "some" statement and it is equally valid. If I ever tell you that some students are male, you can say with certainty that some males are students. What you can't do is combine some statements by linking S/N conditions and read from left to right. If I tell you some students are males, and some males are professional baseball players, you can't tell me that some students are professional baseball players.

I read the Powerscore books probably 6 years ago, but I remember reading something about a "some train" and this is precisely the concept they try to hit home. If you have a chain of inferences, you can reverse the entire train with some. If it's true that Most A are B, then it is true that some B are A. If Most A are B and Most B are C, then some A are C, and similarly, some C are A.


In short, don't study conditional logic by merely trying to memorize a list of things that aren't allowed. Practice questions and develop a strong intuition, and insofar as you decide to keep a list, maintain one that emphasizes positive information rather than negative information. When you solve a question, you have to convert negative information into positive information anyway, so by focusing on the latter, you save time in your thought process.

Hope this helps and good luck!

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arcanecircle
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Re: most/some rules help!! :)

Postby arcanecircle » Wed Oct 17, 2012 3:44 pm

cahwc12 wrote:List-form memorization isn't the way you should focus on understanding these concepts.

+1

bp shinners
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Re: most/some rules help!! :)

Postby bp shinners » Thu Oct 18, 2012 12:24 pm

Here's my mnemonic device for remembering the ways to combine conditional/quantified statements:
the Sufficient condition of the Stronger statement must be Shared, and you get a Some statement.

I call it the 4 Ss. (Shared Sufficient Stronger = Some).

You can't combine two Somes, and you can't combine a Some and a Most, but this works for every other combination of statements (including 2 'All' statements).

The one exception, and it isn't even that, is the following:
Most lawyers are alcoholics
All alcoholics have hangovers at work
________________________________
The shared term is in the sufficient condition of the stronger statement, so we can combine them, and we do get a Some statement. However, for this one exception, we can get a Most statement. It's the one asterisk in the mnemonic device.

Let's check another example that trips people up:
All Michael Bay films feature explosions
All Michael Bay films feature cleavage
__________________________________
The sufficient condition of my stronger statement (in this case, both, since they're tied) is shared, so I can get a Some statement:
Some movies with cleavage feature explosions.




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