Q25 - Some twentieth-century art

[ohthatpatrick]

Question Type:
Inference-EXCEPT

Stimulus Breakdown:
Great art -> original ideas.
Great art -> influential.
Some 20th century art is great art.

Answer Anticipation:
We have a couple conditionals, so we should see if they chain together. They do not, although, we could say that "Great art -> original ideas and influential". We also have a specific fact that might trigger the conditionals. Since some 20th century art is great, we know that some 20th century art is influential, and some 20th century art involves original ideas.

Correct Answer:
C

Answer Choice Analysis:
(A) Can be inferred. We know that some 20th century art is great, which means it is influential and involves original ideas.

(B) Can be inferred. We predicted this.

(C) Cannot be inferred. This tries to create a conditional relationship between "original" and "influential". We weren't given anything like that. This is the same as being told "All NFL players are athletic and all NFL players are wealthy" and then inferring "only athletic people are wealthy".

(D) Can be inferred. This would be diagrammed as "Great art -> influential and involves original ideas"

(E) Can be inferred. We predicted this.

Takeaway/Pattern: The bad inference in choice C shows up commonly on Match the Flaw arguments. The author provides us with "A --> B" and "A --> C" and then makes a faulty conclusion that there must be some conditional relationship between B and C.

#officialexplanation

[yahoo]

So, I had a little trouble with the formal logic in this one.This is how I broke it down:

20th Cent <---->Great Art
Great art ---> Orig. Ideas
~influential----> ~great art

From this I was able to eliminate B & E then I got a little lost. Can someone help me out!

Thanks

[ManhattanPrepLSAT2]

In general, it's difficult to use formal logic notations for sentences such as this first one that involve relationships that are less than absolute --

Knowing that some twentieth-century art is great art is of limited use for us in terms of making inferences. It doesn't guarantee that a piece of twentieth-century art is great or not great, and it doesn't guarantee that great art is or isn't from the twentieth century.

For the first sentence, I think it's best to think of it in its original form:

Some 20th century are is great art.

The next two relationships are more absolute and can more easily be considered in formal notation, and I think you've nailed it:

Great art -- > original ideas.

- Influential --> - great art.

Note that this is an unusual EXCEPT version of an inference question. We know that 4 inferences are going to be VALID, so it might be helpful to consider everything we know before going into the answer choices -- that is, the original conditions and their contrapositives (note, because we can't represent the original sentence in conditional notation, we needn't find a contrapositive). We can list them here:

Some 20th century are is great art.
Great art -- > original ideas.
- Original ideas --> - Great art
- Influential --> - great art
Great art --> Influential

We know that 4 answers are going to connect these elements or infer from them correctly. Let's see which answers must be true:

(A) We know for certain that there are some great paintings that are both influential and original. Therefore, we know for sure that some influential art must involve original ideas.

(B) We know some 20th century art is great, and all great art involves original ideas. Added together, we can see that some 20th century art involves original ideas.

(C) connects together two elements -- influential and original -- in a manner that can't be proven by the text.

In formal notation, (C) would translate to I --> O.

(one way to think of which way the arrow should go between I and O is in terms of what you know MUST be true.

Based on this answer, if artwork is influential, it MUST BE TRUE that it involves original ideas. Therefore, I -- > O. (I must mean O).

Based on this answer it doesn't have to be true that if an artwork is original, it must be influential.).

G --> I, and G -- > O, but this does not mean I -- > O.

(D) , in formal notation, would translate to G --> I and O. We know this is true. Since we know that all great art is influential and original, we know that only art that is influential or original can be great (if it wasn't influential or original, it couldn't be great).

(E) can be inferred by combining all three statements we are originally given.

Hope that helps! Please follow up if you have any further questions.

[farhadshekib]

Here is how I approached it:

1) 20th Century ---Some ---> Great Art.

2) Great Art --> Original Ideas.

3) ~ Influential --> ~ Great Art
CP: Great Art --> Influential.

Connect them together and we get this:

20th C ---some --> Great Art --> Original Ideas + Influential Art

Main Inferences:

20th C --some --> Original ideas.
20th C---some --> influential.

Or both!

Original ideas ---some---> Great Art (some original ideas are great art work).

Influential art ---some--> Great Art (some influential art is great art).


(A) We know that all Great Art = original + influential.

So, it must be true that some - or at least one - influential art work involves original ideas, since all great art is both influential and original

(B) 20th C -- some --> original ideas. (Yup, see diagram above).

(C) Influential --> Original ideas (not supported by our diagram).

(D) Great art --> influential + original ideas (Yup, see diagram above).

(E) 20th C ---Some---> influential + original ideas (Yup, see diagram above).

Hope this helps.

[kevin]

Thank you all for your help with this question.

I am having difficulty understanding a concept here:

It seems from the VALID answer choices that this relationship must be true (I'm referencing answer choice A)

If we have a relationship as follows:

A ---> B and C

Then:

Some B's are C's and Some C's are B's?

When taking this question the first time, I eliminated all the answers except for choices A and C. I clearly see why answer choice C is the correct answer (an invalid logical assumption), however I did not know that the necessary conditions have this "some" correlation. I'm assuming that we CANNOT interchange "some" with "most" in these scenarios however...as that would be too far of an inference to make.

[timmydoeslsat]

If we have a relationship as follows:

A ---> B and C

Then:

Some B's are C's and Some C's are B's?

That is correct. If we do in fact have A, then we will have A, B, and C all occurring. So we will have a commonality of these variables with each other.

And some statements are reversible of course, as you have pointed out. Most statements are reversible too, but when you reverse a most statement, it becomes a some statement.

A most B...reversed...becomes...B some A

[alexg89]

In a case such as A < G > B you can properly infer that some A's are B's. With this in mind you can eliminate answer choice A.

A uses I < GA > OI.

[mitrakhanom1]

I'm having a hard time understanding answer choice D and C. Why is C right and D wrong. How is it that "only art that is influential and involves original ideas is great art" for answer choice D is a correct statement?

I used conditional logic to figure this out.

Some twentieth-century art is great art.
TCA-some--> GA

All great art involves original ideas
GA---> OI

Any art that is not influential cannot be great art
~AI--->~GA
contrapositive GA---> AI

I was able to make various deductions.
TCA-some--> GA
GA---> OI
TCA-some--> OI

TCA-some--> GA
GA---> AI
TCA-some--> AI

I thought when you take
GA---> OI
GA---> AI
you get:
OI<-some--> AI

I didn't realize you could do this:
GA--->OI
GA---> AI
GA---> AI and OI

But for answer choice D you get GA---> AI + OI. I didn't know you can combine them this way. I thought its only for the logical games section that you can add them together this way. But I guess its valid for LR too?

[christine.defenbaugh]

I didn't realize you could do this:
GA--->OI
GA---> AI
GA---> AI and OI

But for answer choice D you get GA---> AI + OI. I didn't know you can combine them this way. I thought its only for the logical games section that you can add them together this way. But I guess its valid for LR too?

Yep!! It's so useful to be able to combine conditionals in that way!

Remember, things you learn about conditionals are true no matter where the conditionals show up - ways to translate, how to get the contrapositive, which statements you can split up or combine; if it's true in logic games, it's also true in LR.

Consider the logic for a moment. Take these two statements:

If you give me chocolate, I will tap dance.
If you give me chocolate, I will sing.

Taking both of those statements as truth, is it not accurate to say that if you give me chocolate, I will both sing and tap dance?

I thought when you take
GA---> OI
GA---> AI
you get:
OI<-some--> AI

This is actually only true when you know that there actually IS some GA in existence. Then, whatever that GA was would be both OI and AI, and therefore there would be at least one OI in the world that is AI. In this question, we have that, because we know that some 20th Century art is GA, and is therefore both OI and AI (and that's answer choice (E). Since at least one 20th Century piece of art is GA, OI, and AI, that means I can say some OI are AI!

Interestingly, the only way we can get to the realization that some OI are AI is to first realize that anything that is GA is BOTH of those two things - and that's the combined conditional above (GA --> OI + AI).

Please let me know if this helps clear a few things up!