#19 - None of the students taking literature are taking

[srcline@noctrl.edu]

Hello,

So I read over Rachel and Luca's post and they helped clear up the first two rules, but I'm still a bit confused on the third part of the stimulus.

So "none of the students taking rhetoric are taking physics" so doesn't this mean that those students that are taking rhetoric are NOT taking physics? I'm still confused on how to combine these.

Thankyou
Sarah

[Jonathan Evans]

Sarah,

Yes, you're right. If you're taking rhetoric, you're not taking physics. These kinds of conditionals sometimes invite students to miss the forest for the trees. You get so caught up symbolizing stuff that you forget to notice what actually is going on.

Let's break it down.

The lit students don't take physics.

The rhet students don't take physics.

Some physics students take art.

Okay. What connections can we make. The only common variable is physics. What does physics connect? Physics is the link here.

We know literature and rhetoric students don't take physics. Great. Do we know anything about them with respect to each other? No.

However, we know there are physics students who take art. So what? So these physics students who take art are neither literature students nor rhetoric students. Bingo. That's your connection.

Answer choice (A) gives it to you on a silver platter. The rest of the answers just shift the pieces around in a bunch of garbage.

The key is prephrasing. Recognize the essential connections. Try to anticipate where the author is going with his statements.

[Nikki Siclunov]

Hi Sarah,

To add to Jonathan's excellent response above, this question uses Formal Logic, which is outlined in the Logical Reasoning Bible (under the chapter titled Formal Logic), and also in the Virtual Module under Lesson 8 of our Full-Length LSAT course.

Here's the Formal Logic diagram for the relationships in this stimulus:

• 1. LIT PHY ART
  
  Therefore, ART LIT

Since a "some" statement can be read backwards, we know that some Art students take Physics. However, no Physics students take Literature. Therefore, some Art students don't take Literature (answer choice A).

• 2. RHET PHY ART
  
  Therefore, ART NO RHET

By the same line of reasoning, we can also conclude that some Art students don't take Rhetoric.

Note: Just because there are students taking art but not literature does not mean that there are students taking both art and literature. The inference of the type "ART LIT" is not available to us given the information provided.

Hope this helps!

[srcline@noctrl.edu]

Hello, Jonathan and Nikki

Yes this makes sense, While I was reading Jonathan's response I was thinking that this sounds like an inference that those physics students who are taking art, means that these students dont take lit or rhetoric. I think the formal logic part was throwing me off b/c I was getting caught up with the sufficient and necessary conditions.

Thankyou
Sarah

[chloemeyers]

Hi! I initially did this question as a conditional reasoning problem and answered with B. I understand the diagram after reading through these posts but still have 2 questions:

1. How do you know when a question is formal logic versus conditional? I diagramed these none statements in a conditional reasoning format, although I messed up on my diagramming (even though it wasn't actually conditional). I put the statement modified by none as the necessary condition, however looking at my notes I believe that the none statement is the sufficient condition and the necessary condition is negated, is that correct? Either way I now see that this is not a conditional reasoning problem, however I am still having problem identifying why that is so.

2. What is the difference between answer choices A and B? From the explanations given above I understand how A is correct, however I can't seem to see a difference between the two answer choices.

Thanks so much!

[Jeremy Press]

Hi Chloe,

There's a little bit of overlap between the "formal logic" sphere and the "conditional reasoning" sphere. To help make it clearer for yourself, formal logic is the term we use for claims establishing specific quantitative relationships between things. Generally, those claims will utilize the following terms or their synonyms: all, most, some, none. So, in this stimulus there are three statements utilizing those terms (or synonyms). The first and last use "none," and the second uses "several" (which, for formal logic purposes, has the same logical implications as the term "some").

Within formal logic, though, some claims can be understood (and should be diagrammed) conditionally (which means they have a contrapositive). Those are claims using the terms "all" and "none" (and their synonyms). So diagramming the "none" statements as conditional was not a mistake! Although, as you note, you have to make sure you've got the terms in the right places, with the proper negations. Your clarification of the diagramming of "none" statements is correct: the term modified by "none" gets diagrammed as the sufficient condition. The remaining term is negated and then diagrammed as the necessary condition.

With answer choice B, nail down what we know from the stimulus: We know that if you're taking literature, you're not taking physics. So that means you're not one of those "several" physics students taking art. But are there other art students? There could be. So the literature students could potentially be among those other students who could be taking art. And that's how we know that answer choice B doesn't have to be true (although it could be true).

I hope this helps!

Jeremy

[PresidentLSAT]

I'm really excited here because I read the explanations and I think I know how to diagram. I also gained some insight here that we can always reverse 'some' arguments without negation errors.

Here's my diagram. Let me know if I'm correct:

(No lit student is enrolled in Physics) L->-P
No Rhe student is enrolled in Physics) R->-P


(Some Physics are enrolled in art) ¬P->A
Revered: ¬A->P

The Contrapositive of the first premises gives us: P->-L & P->-R
Combined with our 'some' argument, we get ¬A->P->-L (Some A who are enrolled in P but not enrolled in L)
We also get: ¬A->P->-R (Some A who are enrolled in P but not enrolled in R)

[Jeff Wren]

Hi PresidentLSAT,

It looks like you got the hang of it, although your diagramming symbols are a bit different than ours.

The important point is that this question involves a concept called Formal Logic, which is not as common as on the test as it used to be.

For a detailed discussion of this topic, go to the lesson 8 homework online for our LSAT course or check out chapter 13 in The Logical Reasoning Bible.