Besides PowerScore, Who Offers Good Lessons on Formal Logic? Forum

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[sumus romani]

Take a logic class in college. The "some train" stuff is relevant for only around one or two questions per test. If you insist on learning it, then you have to take a logic course with symbolic logic in it. What you are looking for is a textbook with an upside-down 'A' and backwards 'E'. I am not making this up.

[Audio Technica Guy]

Take a logic class in college. The "some train" stuff is relevant for only around one or two questions per test. If you insist on learning it, then you have to take a logic course with symbolic logic in it. What you are looking for is a textbook with an upside-down 'A' and backwards 'E'. I am not making this up.

You don't really need to take a class in symbolic logic for this. There are only 3 rules when it comes to what powerscore calls "formal logic"

1) Positive quantity reversal: That is any time a positive quantity goes in one direction, some comes back in the opposite direction. That is (insert positive quantity word) A's are B's implies some B's are A's

Examples:

All A's are B's --> some B's are A's
Most A's are B's --> some B's are A's
Some A's are B's --> some B's are A's

2) Multiple mosts rule: Any time you have two or more mosts (or greater) coming out of one group, then "some" connects the two groups that the most are going to.

Examples:

Most A's are B's, Most A's are C's --> Some B's are C's
All A's are B's, most A's are C's --> Some B's are C's
Most A's are B's, most A's are C's, Most A's are D's --> some B's are C's, some B's are D's and some C's are D's

3) All jump rule: Any time all goes from one quantity to another, whatever goes into the first quantity then get's to jump directly into the second.

Examples:

Some A's are B's, all B's are C's --> Some A's are C's
Most A's are B's, all B's are C's --> Most A's are C's
All A's are B's, all B's are C's --> All A's are C's

It's kind of hard to give a written explanation of these rules, at least in the context of a message board, but people run into trouble mostly when they make them more complicated than they are.

[MagnumLifeStyle]

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[Audio Technica Guy]

Audio Technica Guy,

As always, thanks for your clarification -- simply brilliant.

I've read in your previous posts that you've written some text for a test prep company. Do you sell them online?

I work for Princeton Review. Yes, you can buy TPR books online from amazon. The books are okay, but mostly what I do is work with the classroom part of our company. There may or may not be some of the problems I've made up and some of the explanations I've contributed in the books you can buy on Amazon. To be honest I'm not sure. I periodically get a very small royalties check from TPR, but I'm really not sure what its for anymore.

[MagnumLifeStyle]

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[Audio Technica Guy]

I've never read or used anything from Princetown Review.

Is their method radically different from PowerScore's to merit some difficulty in adjusting?

In other words, would you recommend those who are used to PowerScore to also may be try Princetown Review?
Are both compatible?

Princeton Review's primary strength is in its class offerings especially our 24 class, 84 hour hyperlearning class. The prep books we sell at like Borders or Amazon are okay, but to be honest they're not really any better than any of the other companies' prep books. If you've started with the powerscore bibles, I'd probably just stick to those.

[Entchen]

I really like The Logic Book by James Moor. New it's like $90, but you can find used copies online for like...$5. See: http://www.campusbooks.com/books/nonfic ... ition.html

It was the book we used in my undergrad intro logic class. And, in the interest of full disclosure, he was my professor (though for a different class). It is more formal logic than you will need for the LSAT, but it's fun and will get you thinking the right way.

Good luck!

[barnum]

2) Multiple mosts rule: Any time you have two or more mosts (or greater) coming out of one group, then "some" connects the two groups that the most are going to.

Examples:

Most A's are B's, Most A's are C's --> Some B's are C's
All A's are B's, most A's are C's --> Some B's are C's
Most A's are B's, most B's are C's, Most A's are D's --> some B's are C's, some B's are D's and some C's are D's

The bolded part is not correct. If you have most As are Bs and most Bs are Cs, then no inference can be made. As Audio said in the rule the two mosts must be coming out of one group. In the bolded part, the first most is with the A and in the second the most is with the B, then no inference is possible.

[barnum]

3) All jump rule: Any time all goes from one quantity to another, whatever goes into the first quantity then get's to jump directly into the second.

Examples:

Some A's are B's, all B's are C's --> Some A's are C's
Most A's are B's, all B's are C's --> Most A's are C's
All A's are B's, all B's are C's --> All A's are C's

This bolded rule may also be a bit misleading. This is only true if the second statement is the "all" statement. For example

All As are Bs, Some Bs are Cs, then no inference would be possible.

[Audio Technica Guy]

2) Multiple mosts rule: Any time you have two or more mosts (or greater) coming out of one group, then "some" connects the two groups that the most are going to.

Examples:

Most A's are B's, Most A's are C's --> Some B's are C's
All A's are B's, most A's are C's --> Some B's are C's
Most A's are B's, most B's are C's, Most A's are D's --> some B's are C's, some B's are D's and some C's are D's

The bolded part is not correct. If you have most As are Bs and most Bs are Cs, then no inference can be made. As Audio said in the rule the two mosts must be coming out of one group. In the bolded part, the first most is with the A and in the second the most is with the B, then no inference is possible.

Yeah, made a mistake there. The "most B's are C's" was supposed to say "most A's are C's". Sorry for the typo and any confusion it may have brought about.

I fixed it in my original post now.

[Audio Technica Guy]

3) All jump rule: Any time all goes from one quantity to another, whatever goes into the first quantity then get's to jump directly into the second.

Examples:

Some A's are B's, all B's are C's --> Some A's are C's
Most A's are B's, all B's are C's --> Most A's are C's
All A's are B's, all B's are C's --> All A's are C's

This bolded rule may also be a bit misleading. This is only true if the second statement is the "all" statement. For example

All As are Bs, Some Bs are Cs, then no inference would be possible.

I think it's correct as written, it's just hard to explain without a visual. What I mean by "first quantity" is what the all is coming from. So if all A's are B's is the statement, I would call A's the first quantity. Whatever goes into A's gets to jump into B's. Again, kind of awkward to word, but easy enough to show with diagrams.