Q18 - Obviously, we cannot in any

[mcrittell]

Would this be correct thinking?

MP

EP-->NS
NS-->EP

MP-->NS-->EP
EP-->NS-->MP
EP-->MP

[rsmorale]

I'd also like to know this as well.

[timmydoeslsat]

It is hard to follow with the different colors and no visible negations. I assume the red color is the negated version of the statement.

I will post my thoughts of what I just did with this question and how I approached it.

First sentence: Seems like a conclusion I bet! I will keep that in my mind as I read more.

Second sentence:

If Plant ---> ~NS
If Exp.Pain ---> NS
----------------------
~ Mistreat Plants

So I now know the first sentence was the conclusion.

If Plant ---> ~NS
If Exp.Pain ---> NS
----------------------
~ Mistreat Plants

I notice that I can spin the second sentence around and have it connect with ~NS to form a long chain. This is not necessary to do however.

If P ---> ~NS ---> ~EP
----------------------
~ Mistreat Plants

So what would I like to know to give me this conclusion of not mistreating plants. I know that mistreating plants is not in the premises, so the answer choice of a sufficient assumption will have to give us that bridge. Eliminate B and C.

Go to A and look.

A) EP ---> Mistreated.

Will not allow us to conclude that we cannot mistreat plants. We about those things that do not experience pain (like plants!) This does not bridge that gap.

B) Has already been eliminated.
C) Has already been eliminated.

D) Mistreated ---> EP

Yes! Looks good. We know that the contrapositive is ~EP--->~Mistreated.

Look back at our long chain. We know that if plant then not experience pain. This assumption goes from not experience pain to not mistreated.

E) Eliminate for the same reason as (A) essentially. If NS ---> Mistreated.

What about those that do not have nervous systems! Does not bridge the gap.

[mcrittell]

Of course the red is negation.

[lhermary]

I'm experiencing pain with this question....

Can you go into more detail as to why D is the answer and not A?

Why does 'experience pain' have to be the necessary condition and not the sufficient?

Normally I can do these types of questions however the lack of conditional logic in the conclusion has thrown me off and I don't know what to look for.

[ManhattanPrepLSAT1]

I see your confusion lhermary. And it's not totally without justification. If you look at the last sentence it says that having a nervous system is necessary to experience pain. So it sounds like the term "experience pain" should be the sufficient condition.

The reason why the correct answer has "experience pain" in the necessary condition and not the sufficient one is that this is not an Inference question - it's a Sufficient Assumption. So rather than extracting information we know to be true, we need to add something to the argument that hasn't been stated.

The argument looks like

EP ---> NS
~NS
-------------
~MT

Notation Key: EP - experience pain, NS - nervous system, MT - mistreated

The evidence would allow us to simplify the argument before we look for the assumption

~EP (can be inferred from the stated evidence)
------
~MT

The assumption is thus

~EP ---> ~MT

and by contrapositive

MT ---> EP

Hope that helps!

[mxl392]

So what you're saying is that although B is consistent with the stimulus, it's not the right answer because it is the exact same as a premise?

[timmydoeslsat]

Answer choice B is repeating a premise alreaady given in the argument. The question stem wants us to use an answer choice to plug into the argument and have the conclusion follow logically.

As you can tell, the evidence in the argument does not mention mistreatment, yet the conclusion does. We must have something about mistreatment in evidence to conclude something about it. Answer choice B does not offer anything about mistreatment. So it will never allow for the conclusion to follow logically.

[Carlystern]

I see your confusion lhermary. And it's not totally without justification. If you look at the last sentence it says that having a nervous system is necessary to experience pain. So it sounds like the term "experience pain" should be the sufficient condition.

The reason why the correct answer has "experience pain" in the necessary condition and not the sufficient one is that this is not an Inference question - it's a Sufficient Assumption. So rather than extracting information we know to be true, we need to add something to the argument that hasn't been stated.

The argument looks like

EP ---> NS
~NS
-------------
~MT

Notation Key: EP - experience pain, NS - nervous system, MT - mistreated

The evidence would allow us to simplify the argument before we look for the assumption

~EP (can be inferred from the stated evidence)
------
~MT

The assumption is thus

~EP ---> ~MT

and by contrapositive

MT ---> EP

Hope that helps!

Is there a rule that the (~) transfers to the EP or something?

I keep coming to this:

EP---> NS
~NS
--------------
~MT

I don't understand how that turns into this inference:

~EP (<-----how does this become negative and still stays in the sufficient side?)
----------
~MT (<----since this is the "conclusion" does this have a special side (S/N) we should assume it belongs to?)

Ugh.

Carly

[Carlystern]

Is it the same as a positive and a negative = negative? Is that why EP becomes negative in the sufficient?

[ohthatpatrick]

I think what might be troubling you is that we need to actually combine the two premises to make the inference that "Plants can't experience pain". I don't see that represented in your notation, but that's supposed to be part of how we understand the premises.

As you wrote:

Premises:
EP---> NS
~NS

Right there you have a conditional idea and a statement of fact. Does the statement of fact tell you anything, based on the conditional rule?

Yes. The conditional rule looks like this:
EP --> NS
~NS --> ~EP

The statement of fact is ~NS.

Okay, well, then we can infer ~EP.

(If this is confusing you on a symbolic level, get back to the conversational simplicity of "you need a nervous system to experience pain, but plants don't have a nervous system." Okay, well then what do you know about plants? We know that plants can't experience pain).

So you would want to amend your diagram of the argument to reflect this fact we're supposed to be inferring.

EP---> NS
~NS
~EP
--------------
~MT

Because of where the premises leave us and because of what we're trying to prove in the conclusion, the missing link we need is

~EP --> ~MT
(or MT --> EP)

Does that make sense? That's what (D) says: "if you can't experience pain then you can't be mistreated".