PrepTest 34, Section 3, Question 17 (necessary assumption) Forum

[Oscar85]

I keep getting this question wrong, and I cannot understand why. Usually necessary assumption questions with conditionals mess me up, especially when the stimulus is not clear about conditional cues. Can someone help me reason through this one so that I may be able to handle other questions with a similar structure?

I reasoned that A and B cannot be the answers, because it does not say anything about entertaining abstract ideas.

C, D, and E seem to be more difficult, however.

Here is the core I constructed:

animals can signal each other with sounds and gestures + it does not prove that animals possess the ability to use sounds or gestures to refer to concrete objects of abstract ideas --> This does not confirm that animals possess language (so animals do not possess language)

I *think* I can eliminate C because it doesn't mention anything about language, which appears to be the missing link.... And about animals - I just don't know what to negate. Would the negated statement be no animals that possess a language can refer to both concrete objects OR (?) abstract ideas....

Help?

[Oscar85]

Could the stimulus be read as: ~P or ~G . Conclusion: ~L

Therefore, (D): ~P or ~G --> ~L

??

Thanks guys.

[CardozoLaw09]

SSG = system of sounds and gestures
CO = concrete objects
AI = abstract ideas
L = language

D) SSG --> ~(CO or AI) --> ~L

Argument:

Premise:
SSG --> ~(CO or AI)

Conclusion:
SSG --> ~L

This is how I'd diagram it but take it with a grain of salt. The argument makes the jump from the premise to the conclusion that a system of sounds and gestures isn't sufficient to prove animals have language. The missing link is the necessary component of the premise which answer choice D touches upon. There's a good chance I'm wrong though, hopefully someone can enlighten the both of us! Necessary assumptions are my weakness as well

[Nova]

I dont have it in front of me, but this might help http://www.manhattanlsat.com/forums/q17 ... 263c15bf98

[cc.celina]

This is my read on the question:

Since the zoologist's argument doesn't seem to contain a really easy logic chain, I didn't start off by diagramming this one. The zoologist says that sounds and gestures don't prove that animals possess language. Why? Because it doesn't prove that animals use sounds and gestures to refer to (1) concrete objects or (2) abstract ideas.

We can infer from this that the zoologist thinks that if you don't refer to concrete objects or abstract ideas, you don't possess language. (He doesn't say this directly: he ASSUMES this. It is therefore a necessary assumption.) Which means that the ability to refer to concrete objects and abstract ideas is necessary to language.

We can now diagram our simplified, bolded statement:
Language (sufficient condition) --> Concrete objects OR abstract ideas

Taking the contrapositive of this simplified statement:
~Concrete objects AND ~abstract ideas --> ~Language

D captures this perfectly by saying: if neither of the necessary conditions (referring to concrete objects OR referring to abstract ideas) are met, then it's not a language.



On to the wrong answers:

You can't pick C because the zoologist merely says that you can't PROVE animals possess language. He doesn't say that animals DON'T POSSESS language. This is important: As a general rule, disproving evidence for a conclusion does NOT disprove the conclusion. C exploits the logical fallacy of saying "Because we can't prove the conclusion, the conclusion isn't true."

You can't pick E because, well, we don't even know if any animals possess language, and the zoologist is arguing that you can't prove that they can through their signaling system, so it's definitely not a necessary assumption to his argument.

I hope that was clear. Definitely check out Nova's link if it wasn't.

[Oscar85]

This is my read on the question:

Since the zoologist's argument doesn't seem to contain a really easy logic chain, I didn't start off by diagramming this one. The zoologist says that sounds and gestures don't prove that animals possess language. Why? Because it doesn't prove that animals use sounds and gestures to refer to (1) concrete objects or (2) abstract ideas.

We can infer from this that the zoologist thinks that if you don't refer to concrete objects or abstract ideas, you don't possess language. (He doesn't say this directly: he ASSUMES this. It is therefore a necessary assumption.) Which means that the ability to refer to concrete objects and abstract ideas is necessary to language.

We can now diagram our simplified, bolded statement:
Language (sufficient condition) --> Concrete objects OR abstract ideas

Taking the contrapositive of this simplified statement:
~Concrete objects AND ~abstract ideas --> ~Language

D captures this perfectly by saying: if neither of the necessary conditions (referring to concrete objects OR referring to abstract ideas) are met, then it's not a language.



On to the wrong answers:

You can't pick C because the zoologist merely says that you can't PROVE animals possess language. He doesn't say that animals DON'T POSSESS language. This is important: As a general rule, disproving evidence for a conclusion does NOT disprove the conclusion. C exploits the logical fallacy of saying "Because we can't prove the conclusion, the conclusion isn't true."

You can't pick E because, well, we don't even know if any animals possess language, and the zoologist is arguing that you can't prove that they can through their signaling system, so it's definitely not a necessary assumption to his argument.

I hope that was clear. Definitely check out Nova's link if it wasn't.

Aha! So was it like I said?

The for, thus construction is the same as what you put, I think....

Since no ability to use sounds or gestures to refer to concrete objects or abstract ideas, conclusion: no language.

Like you said, since it doesn't use conditional language, you don't immediately go into diagramming mode... But what you said cleared it up, thanks. The Manhattan link just makes it that more confusing haha.

[Nova]

The Manhattan link just makes it that more confusing haha.

Lol sorry. In general they have pretty good explanations.

[cc.celina]

Could the stimulus be read as: ~P or ~G . Conclusion: ~L

Therefore, (D): ~P or ~G --> ~L

??

Thanks guys.

Aha! So was it like I said?

The for, thus construction is the same as what you put, I think....

Since no ability to use sounds or gestures to refer to concrete objects or abstract ideas, conclusion: no language.

I'm not entirely sure what you meant by P and G: does P stand for concrete objects and G for abstract ideas?

If so, then you are almost right with your conditional statement: Remember when you take the contrapositive, "and" becomes "or" and vice versa. So it would be:
~P and ~G --> ~L
Which is what D says.

This might be nitpicky, but one more small note: When you ask if the stimulus could be read this way, that is technically incorrect. The stimulus can't be read that way, because this conditional statement is exactly what is MISSING from the stimulus. That is why it is an assumption. So you skipped a step ahead: You didn't diagram the stimulus, but you intuited what you SHOULD have diagrammed if the zoologist had made a stronger argument.

[CardozoLaw09]

This is my read on the question:

Since the zoologist's argument doesn't seem to contain a really easy logic chain, I didn't start off by diagramming this one. The zoologist says that sounds and gestures don't prove that animals possess language. Why? Because it doesn't prove that animals use sounds and gestures to refer to (1) concrete objects or (2) abstract ideas.

We can infer from this that the zoologist thinks that if you don't refer to concrete objects or abstract ideas, you don't possess language. (He doesn't say this directly: he ASSUMES this. It is therefore a necessary assumption.) Which means that the ability to refer to concrete objects and abstract ideas is necessary to language.

We can now diagram our simplified, bolded statement:
Language (sufficient condition) --> Concrete objects OR abstract ideas

Taking the contrapositive of this simplified statement:
~Concrete objects AND ~abstract ideas --> ~Language

D captures this perfectly by saying: if neither of the necessary conditions (referring to concrete objects OR referring to abstract ideas) are met, then it's not a language.



On to the wrong answers:

You can't pick C because the zoologist merely says that you can't PROVE animals possess language. He doesn't say that animals DON'T POSSESS language. This is important: As a general rule, disproving evidence for a conclusion does NOT disprove the conclusion. C exploits the logical fallacy of saying "Because we can't prove the conclusion, the conclusion isn't true."

You can't pick E because, well, we don't even know if any animals possess language, and the zoologist is arguing that you can't prove that they can through their signaling system, so it's definitely not a necessary assumption to his argument.

I hope that was clear. Definitely check out Nova's link if it wasn't.

Soooo exactly what I said? Thanks

[cc.celina]

Soooo exactly what I said? Thanks

Lol, sorry if I was being redundant. I was trying to come up with an explanation that didn't rely on diagramming the original stimulus, because that's not how I would have approached it. Your approach works too, but my brain doesn't work that way.

[Oscar85]

Could the stimulus be read as: ~P or ~G . Conclusion: ~L

Therefore, (D): ~P or ~G --> ~L

??

Thanks guys.

Aha! So was it like I said?

The for, thus construction is the same as what you put, I think....

Since no ability to use sounds or gestures to refer to concrete objects or abstract ideas, conclusion: no language.

I'm not entirely sure what you meant by P and G: does P stand for concrete objects and G for abstract ideas?

If so, then you are almost right with your conditional statement: Remember when you take the contrapositive, "and" becomes "or" and vice versa. So it would be:
~P and ~G --> ~L
Which is what D says.

This might be nitpicky, but one more small note: When you ask if the stimulus could be read this way, that is technically incorrect. The stimulus can't be read that way, because this conditional statement is exactly what is MISSING from the stimulus. That is why it is an assumption. So you skipped a step ahead: You didn't diagram the stimulus, but you intuited what you SHOULD have diagrammed if the zoologist had made a stronger argument.

yeah, I messed up with the conditional diagramming.

And hmm... I'll try explain myself. So the stimulus:

conclusion: [the fact that animals can signal each other with sounds and gestures] does not confirm the thesis that animals possess language.

Reasoning: It does not prove that animals possess the ability to use sounds or gestures to refer to concrete objects or abstract ideas.


Assumption: something along the lines of using sounds + gestures to refer to concrete objects of abstract ideas.

My problem: I don't know how to extract the necessary and/or sufficient conditions from the argument without the cues... how were you guys able to do that? That's what seems to be giving me trouble.

Also, if I had broken it down like that, that would be the correct approach to a necessary assumption question, correct?

[cc.celina]

My problem: I don't know how to extract the necessary and/or sufficient conditions from the argument without the cues... how were you guys able to do that? That's what seems to be giving me trouble.

Lol, at least for this one, I was able to tell where he had missed a necessary assumption because the conclusion made me go "wtf." Anytime something pops up in the conclusion when it doesn't appear anywhere else (in this case, the word "language"), there is some shady assumption business going on.

It might help to identify each premise and the conclusion and see where there's a missing link:
P1: Animals can signal to each other via sounds/gestures
P2: Animals signaling to each other doesn't prove that these sounds and gestures can be used to refer to concrete objects or abstract ideas
Conclusion: Animals signaling to each other doesn't prove that animals possess language

You can see that the language thing sorta comes right out of nowhere. Anytime that happens, you know there is an unstated necessary assumption that connects the premises to that out-of-nowhere concept. In this case, you need to connect the idea of referring to concrete objects/abstract ideas to the idea of possessing language.

[cc.celina]

And because this hasn't been mentioned before, this is a good place to use the negation test. If on a necessary assumption question you can't figure out which one it is, use process of elim by negating each answer choice until the argument falls apart. Try negating D: If a system of sounds or gestures contains no expressions referring to concrete objects or abstract ideas, then that system could still be a language. Well, that's not what the zoologist is saying at all, and it completely undermines his argument. So D is the correct answer.

[Oscar85]

And because this hasn't been mentioned before, this is a good place to use the negation test. If on a necessary assumption question you can't figure out which one it is, use process of elim by negating each answer choice until the argument falls apart. Try negating D: If a system of sounds or gestures contains no expressions referring to concrete objects or abstract ideas, then that system could still be a language. Well, that's not what the zoologist is saying at all, and it completely undermines his argument. So D is the correct answer.

I did use the negate test lol. But C still sounded right to me. I just find it difficult determening when to negate the quantifier and when to negate the central verb.