Setup and Rule Diagrams

[Steve10297]

Hello,

Have a bit of trouble understanding the information that is presented on page 347 of the 2016 edition of the Logic Games Bible. At the top of page 347, it says "R or Y must appear in each picture." Why is that so? There is not rule that states that. Can someone help?

[Nikki Siclunov]

Hey Steve,

Thanks for your question!

R or Y must appear in each photograph thanks to the third rule. The third rule states that R must appear in every photograph that Y does not appear in (NOT Y R). By the contrapositive, Y must appear in every photograph that R does not appear in (NOT R Y). Accordingly, either R or Y (or both) must appear in every photograph.

This deductive process is explained in detail on pages 342-343.

Check out this blog post, which should clarify the application of this type of rule further:

http://blog.powerscore.com/lsat/the-mos ... -rule-lsat

Hope this helps! Let us know.

Thanks,

[Dave Killoran]

This morning I received the following question:

I know this is a dumb question but I need some clarification. On Dec 2004 LSAT LG 3: a rule states Raimundo appears in every photograph that Yakira does not appear in. So I diagrammed it as not R then Y. wouldn't the contrapositive be Not Y then R? I reviewed a video lesson and it said that If not R then Y is free variable? which the #1 on the game was B which include R and Y. I just don't understand how the rule effects the game. Help!

First, there are never any dumb questions! I know people say that a lot, but it is still true. One small misunderstanding can sink you on a game, so if you ever are even a bit uncertain, ask! Second, this is a really tricky game, and they intentionally worded the rules in an unusual way in order to get students messed up. Basically, the first two rules look like "B appears when A appears" (A B), and the third rule looks like "B appears when A does not appear" (A B). So, the necessary condition is being presented first, and the sufficient condition appears later in the sentence (which is very normal and acceptable). Thus, the first two rules would be diagrammed as:

• S W
  
  U S
  
  (and those two can be combined to form the chain diagram: U S W )

With the third rule, we have a negative on the sufficient condition, leading to the following diagram:

• Y R

So, if Y is NOT in a photograph, then R must be in that photograph. The contrapositive both reverses and negates the terms, and appears as follows:

• R Y

When those two rules are considered together, the mean that if one of R or Y is absent from the photograph, then the other must be in the photograph. In other words, at least one of R/Y is always in a photograph(and possibly both). Rules like this,w here the sufficient condition is negated, are extremely tricky. I wrote an article about them that I think you would find worthwhile. It's called The Most Dangerous Conditional Rule on the LSAT and it explains exactly how rules like this work.

Ok, so when we look at your diagrams, it looks like you did great! You did it in reverse order from me, but that doesn't matter at all. A statement and its contrapositive are identical in meaning, so whichever is "first" is irrelevant.

As for the video lesson you reviewed, it definitely wasn't one of ours because we wouldn't say that if Y occurs then R is "free." In fact, it's not free at all—if Y, then R must be in that photograph. Could they have meant that if Y was in the photograph, then R was free? Because that would be true.

Hopefully that clears this rule up. It's a tough one, so make sure you are 100% comfortable with it. Please let me know what you think. Thanks!

[chelseapkirk]

Hi,

I am having a lot of trouble with Game #3: December 2004 Questions 13-17 (Page 350 of Logic Games Bible textbook).

"Wendy appears in every photograph that Selma appears in"

I did a mistaken reversal. It's supposed to be

S---> W

I put W---> S

I look at the box on necessary/sufficient indicators on page 60 of the textbook and all I see in this is "every" as a sufficient indicator. Can you please deconstruct the sentence for me and explain more clearly why is it S--> W and not W--> S

[Emily Haney-Caron]

Hi chelseapkirk,

GREAT question. This one is tripping you up because of the order of the words. "Every" happens closest to Wendy, so it seems like it is a sufficient indicator for Wendy, right? But if you think about who "every" is actually about, it is Selma; you could rephrase this, "Every photograph that Selma appears in, Wendy appears in" and it would mean the same thing. "Every photograph" is about Selma, Selma is the sufficient condition, and Wendy is the necessary condition. With statements like this, it always helps to slow down and think about the actual relationship between the words. Spotting indicators is a great first step! You just don't want to over-rely on it so that you aren't still piecing out what the indictor is modifying.

[Zestor]

Hello, I am practicing this game in the LG bible book, and I seem a bit confused regarding the relationship between u>s>w>slash r > y relationship. I am able to infer that w>y, s>y, u>y, and slash y>slash w.

But, wouldn't it be correct to also infer that slash y> slash s, slash y> slash u? I am visually trying to make these inferences so i am looking at the u>s>w>slash r > y relationship, and taking the contrapositive of it to arrive at inferences. I am not sure if my process is icorrect.

[James Finch]

Hi Zestor,

The first thing to look for in an undefined grouping game like this is whether we can chain the rules together or not. Here, we definitely can: by taking the contrapositive of rule 3 and the other rules as given, we can create a chain that looks like this:

U S W T and R Y,

leaving Z alone as a wildcard. We can also take the contrapositive of that chain and get:

Y R, R or T W S U

This diagram gives us numerous inferences, and should be used as the main diagram going forward in the game.

Hope this clears things up!

[Jay]

Hello, I just have a simple question.

So, if you read the questions, then I guess, there are multiple photos, either one person appearing alone or multiple persons appearing in one photo, or some could be absent in all photos. This means that if one person(say, T) does not appear in a photo where the other person(say, W) does not appear in, then that one person(say, T) can definitely appear in other photo (or does not appear in any photo at all.)

Now, if you look at rule #4, neither T nor R appear in any photo that W appear in. This means that T and R can still appear in other photo. Right?

also, in rule #3, just because R appear in every photo Y does not appear doesn't mean Y cannot appear in different photo.

However, diagrams in the explanation in LG Bible makes it seem like it is not the case.

for example, for rule #3, if you say, "Not Y" R , it looks like Y doesn't appear in any photo, while Y can still appear in other photo. I guess my problem arises since I initially made two groups: Alone group and Multiple-persons-together group.

Thank you in advance!

[Jeremy Press]

Hi Jay,

The answer to your first question is technically yes: the scenario allows for the possibility that there are multiple different photographs in the album. Thus, if two people cannot appear in the same photograph (like T and W), there could nevertheless be separate photographs, one in which W appears without T, and another in which T appears without W. There could also be separate photographs, one in which W appears without R, and another in which R appears without W. In the rule about Y and R, it's also technically true to say that just because Y does not appear in a particular photograph (which would require R to appear), that doesn't mean Y might not appear in some other photograph in the album.

BUT, here's the reason our diagrams appear the way they do: every rule, and every question in this game, addresses what is required (or possible, or impossible) within a single photograph. The questions don't ask about the album (or other photographs in the album) in a general. So you're never required to think about what's going on in "other" photographs in the album. And hence each question can be approached from the perspective of what's IN the single photograph in the question versus what's OUT of the single photograph in question.

I hope this helps!

Jeremy

[Jay]

Hello Powerscore.

Thanks for the reply. I have another question.

Sometimes it is not clear whether to use Linear Symbolization or Grouping Symbolization.

In this case, is it better to use Linear Symbolization? as in [ S W ] vertical block ?

or is Grouping Symbolization better? as in S -> W. ?

and how do you know which type of symbolization to use ?

Thank you!