【纠结一晚】LR里面Flaw题型疑惑

苍云UID: 3551399

PT66, LRSEC2, 第一题1


Mayor：There has been a long debate in city council about how to accommodate projected increases in automobile traffic. Today, our choice is clear: either we adopt my plan to build a new expressway or do nothing. Doing nothing is not a viable option because our existing system of roads would be in gridlock within ten years given even a conservative estimate of future levels. City council should therefore adopt my plan.



答案是E
It represents a choice that is limited to two options, without giving reasons for not considering any other options.
E确实能够理解，但是这不是针对Mayor的前提提出的Flaw么，做Flaw不是应该默认前提是正确的么，求大神解答

JD@UVAUID: 3503603

Mayor's stated premise is that there are two available choice. To reach his conclusion, his assumption is that these are the ONLY available choices. But that assumption is not supported by any reason, thus flawed.

Here we accept that the stated premise is correct. Then we look at the conclusion derived from the stated premise and focus on the question whether the conclusion is supported by the stated premise.

Ask yourself, “Do the premises, especially as they are stated in the passage, support the conclusion, especially as it is stated in the passage?” In other words, once you discard everything else, how well do the premises support the conclusion? The reason you want to focus on exactly what the premises and the conclusion state is that you do not want to subconsciously make the argument better than it actually is. Do not help the author. Look at what he actually said and then decide whether his evidence stacks up.

Make sure you are not reading anything into the conclusion that is not there. (“Thus, there is no evidence that Mar has life” is very different from “Thus, there is no life on Mars.”)

Wrong answers will often describe a flaw for a conclusion that the argument never actually reached. (For the conclusion saying that there is no evidence of life on Mars, the answer choice which states the argument “presumes, without providing justification, that the lack of evidence for a claim proves that the claim is false” would be wrong because the argument does not conclude that there is no life on Mars –only that there is no evidence of life on Mars.)

JD@UVAUID: 3503603

You can search the Manhattan discussion forum for help. I believe they have threads of almost all the tough questions from previous official LSAT exams with excellent explanations.

Good luck.

苍云UID: 3551399

JD@UVA 发表于 2016-4-5 21:45
You can search the Manhattan discussion forum for help. I believe they have threads of almost all th ...

I really appreciate your replies very much.

I did go to the Manhattan discussion forum. However the threads under this question show that they faced the same problem with me and with no reply. (Somebody asked, Could an expert answer why the flaw is attacking a premise? "The choice is clear: option1 or option 2" is a premise in the argument.)

So the point is that how to distinguish the premise and assumption here. I just cannot understand why we should not take either we adopt my plan to build a new expressway or do nothing as a premise but a assumption.

苍云UID: 3551399

JD@UVA 发表于 2016-4-5 21:45
You can search the Manhattan discussion forum for help. I believe they have threads of almost all th ...

Or maybe there is a rule in LSAT that conditional logic statement like "either A orB" cannot be a premise?

JD@UVAUID: 3503603

I would say that the statement "our choice is clear: . . ." is more like an intermediate conclusion or opinion than a true premise since it is not based on factual evidence but a subjective conclusion by the Mayor.

True, the whole question sounds like attacking the premise . . .

But in reality it is a false dilemma type of question.

苍云UID: 3551399

JD@UVA 发表于 2016-4-5 22:28
I would say that the statement "our choice is clear: . . ." is more like an intermediate conclusion  ...

yeah

So can we conclude safely that in LSAT only the factual evidence can be considered as premises. I'm so worried that I will be puzzled when facing a new question like this.

JD@UVAUID: 3503603

苍云 发表于 2016-4-5 22:39
yeah

So can we conclude safely that in LSAT only the factual evidence can be considered as pr ...

This question is most likely an odd ball. Attacking the premise is the last possible choice for a correct answer when facing a flaw question.

I agree with you in that factual evidence should be considered CORRECT. The same cannot be said about opinions, intermediate conclusions, etc.

The worst case scenario is to eliminate all the wrong answer choices.

joewoo198256UID: 2355635

苍云 发表于 2016-4-5 22:11
I really appreciate your replies very much.

I did go to the Manhattan discussion forum. Howe ...

"either we adopt my plan to build a new expressway or do nothing" definitely is a premise, because mayor uses it to reach his conclusion. But what he didn't say explicitly is "there are only two choices for this question", since an unstated premise is an assumption, we are attacking this unstated premised here, because in order to reach his conclusion, we must admit the correctness of the assumption.

苍云UID: 3551399

JD@UVA 发表于 2016-4-6 00:02
This question is most likely an odd ball. Attacking the premise is the last possible choice for  ...

Thanks a lot！

苍云UID: 3551399

joewoo198256 发表于 2016-4-6 07:47
"either we adopt my plan to build a new expressway or do nothing" definitely is a premise, becaus ...

i disagree.

“either a or b” is tantamount to“there are only two options：a and b”+“one of them should be chosen”

for instance in LG，“either H or J must be inspected on the third day” canbe diagramed like H/J

so if we consider “either a or b” as a premise， “there are only two options” is not an unstated assumption.

joewoo198256UID: 2355635

苍云 发表于 2016-4-6 08:46
i disagree.

“either a or b” is tantamount to“there are only two options：a and b”+“one of ...

Tricky, definitely tricky.

I agree. Like you said, "there are only two options "is embedded within the "either...or..." fashion, it is inherent and fusion of premise/assumption. So by choosing E you can say you are attacking a premise, or you can also say you are attacking an assumption because the two are just cannot be separated from each other. I guess the problem with "either...or..." is that before you use the structure, you have to prove there are only two options here, because "either...or..." is a deductively valid structure, once you admit it you have no way to turn back but to follow the logic chain. So in this regard, it is absolutely an odd ball.

苍云UID: 3551399

joewoo198256 发表于 2016-4-6 09:13
Tricky, definitely tricky.

I agree. Like you said, "there are only two options "is embedded w ...

got it， thanks！

苍云UID: 3551399

最近有新的感受，写下来给需要的同学一个参考吧~

在这个网页里面，发现原来有一种逻辑错误叫False Dilemma说的就是这种情况，看完之后不纠结了，难怪放在第一题Fallacy: False Dilemma