An air traveler in Beijing cannot fly to Lhasa without first flying to Chengdu. Unfortunately, an air traveler in Be...

Valentina July 22, 2020

Why is D incorrect?

Is it incorrect because it doesn't say anything about "two major ways for a person to become fluent in a language"? Additionally, would it be correct if it said, "A person who knows the grammatical rules of a language must have learned them by exhaustive study or growing up in an environment where the language was spoken. Therefore, it is impossible to be fluent in a language unless they learned grammatical rules by exhaustive study or growing up in an environment where the language was spoken."?

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shunhe July 22, 2020

Hi @Valentina,

Thanks for the question! So remember that this is a parallel reasoning question, so we’re looking for something that’s going to match the logical structure of the stimulus. Let’s take a look at that structure. An air traveler in Beijing can’t fly to Lhasa without first flying to Chengdu; in other words, if you flew to Lhasa, you had to have flown to Chengdu.

Lhasa —> Chengdu

Then we’re told that air travelers n Beijing have to fly to Xian before flying to Chengdu. Well “must” introduces a necessary condition, so this is

Chengdu —> Xian

Therefore, the argument concludes, if you file from Beijing to Lhasa, you have to fly to Xian.

Lhasa —> Xian

And we can see that this is true if we chain the above statements

Lhasa —> Chengdu —> Xian

And so we want to replicate the structure of this argument, which in abstract terms is

A —> B
B —> C
Conclusion: A —> C?
Now take a look at (D). It tells us that it’s impossible to be fluent in a language without knowing its grammatical rules. So if you’re fluent in a language, you know it’s grammatical rules.

Fluent in language —> Know grammatical rules

Then we’re told that if you know the grammatical rules, you either learned them through exhaustive and difficult study, or you grew up in an environment where the language is spoken.

Know grammatical rules —> Lots of studying v Grew up in right environment

And then the argument concludes that there are two major ways for a person to become fluent in a language.

So this argument structure is actually

A —> B
B —> C v D
Conclusion: E

And we can see that it’s way different from the structure above, and so isn’t parallel. The conclusion isn’t conditional, there’s an “or” in the second premise, and the conclusion introduces a new term. So (D) isn’t parallel, and is the wrong answer.

Hope this helps! Feel free to ask any other questions that you might have.