Lesson 2 HW Sufficient and Necessary Diagramming Drill

[mgriff]

Hi there,

I have a question about the Sufficient and Necessary Diagramming Drill p. 2-37. I've noticed the one's I got incorrect I am repeating the mistake.

The prompt is "Buying scalped tickets is the only way for Jim to get into the concert."
My reasoning is, if Jim scalped tickets then he will get into the concert.
The contra positive I think is, if Jim does not get into the concert then he did not scalp tickets.

Why is this reasoning incorrect? Thanks !

[Dave Killoran]

Hi Mgriff,

Thanks for the question! When you look at sentences like this, try to think about it less as an exercise in figuring out how the real world works, and more as an exercise in figuring out exactly what the author said. We do it this way because sometimes LSAT authors don't always say the most sensible things

When you are starting out, the easiest way to do that is to follow the conditional indicators in a sentence. So, let's look a the sentence again, and I'll highlight the indicator:

• "Buying scalped tickets is the only way for Jim to get into the concert."

Ok, we know that "only" is a necessary indicator, and it looks like "only" is right by "Jim to get into the concert." But, proximity can be a tricky thing, and what we're really after is what does the indicator modify. And in this case, "only" actually modifies "way." So, whatever that "way" is will be the necessary condition.

In this case, "way" actually refers to "buying scalped tickets." So, "buying scalped tickets" is the necessary condition, and that leaves the remainder—"Jim to get into the concert"—as the sufficient condition, which results in the following diagram:

• Jim gets into the concert Buy scalped tickets

And a contrapositive of:

• Buy scalped tickets Jim gets into the concert

This is a pretty tricky issue overall, so don't worry about the fact that it caused you a problem. If you want to read a bit more about the idea of diagramming "the only way" as well as real world vs LSAT world issues, check out these links:

• http://forum.powerscore.com/lsat/viewto ... p=216#p216
  
  http://forum.powerscore.com/lsat/viewto ... 6166#p6166
  
  http://forum.powerscore.com/lsat/viewto ... =12&t=2479

Please let me know if that helps solve this one. Thanks!

[mgriff]

Thanks the additional links helped, but I think I may need to memorize the indicators in order to fully understand.

[Dave Killoran]

Yes, you definitely need to to do that It's the easiest starting point for understanding all this. The links are for when you want to step past that initial stage and understand what's going on behind the indicators.

Thanks and good luck!