prep 1-75再讨论；附上Ron的解释，不懂，请牛牛指教

兰心寒

cician 发表于 2013-11-16 21:16
明白你的意思啦，谢谢
对于Ron说的 A＝》B不能说明非A＝》非B，你怎么想的呢？这个说法虽然有道理，但是 ...

我印象中，只有阅读里出现的逻辑题，A=>B，才可以推出非A=>非B，就是阅读题里经常出的陷阱，取非。
可是逻辑里，A=>B只能推出非B=>非A，就是原命题等于其逆否命题。
比如，运动可以减肥，只能推出，你没减肥成功，说明你没做运动。
但是你没运动，也许你还在节食，所以你没做运动，不一定你就减不了肥。

cician

兰心寒 发表于 2013-12-2 16:58
我印象中，只有阅读里出现的逻辑题，A=>B，才可以推出非A=>非B，就是阅读题里经常出的陷阱，取非。
可是 ...

明白你的意思辣，谢谢

soulwangh

Hi,

It is a good question.

I think Ron is wrong about this explanation. The reasons are as follows.
1/
This is a correlation to causation question.
Premise: A is correlated with B; Conclusion: A is the cause of B.
In this type of question, the assumption or the gap between premise and conclusion is if and only if A, then B （A和B互为充要条件）and IS NOT If A, then B（A是B的充分条件）

In Ron's word, anything disrupting the CAUSAL relationship between cigarette tax and cigarette consumption --> i.e., any ALTERNATIVE EXPLANATION FOR WHY THE TWO ARE CORRELATED --> will ruin the argument.  
Thus, if you can find any other explanation instead of the tax that can explain the decrease of cigarette consumption, you ruin this argument.
On the other hand, if you can eliminate this possible third factor or explain why this factor is unavailable, you strengthen the argument.

If Ron’s explanation is right, why B is correct?  B and C are on the same line of reasoning.

2/
Why C is wrong?
In my opinion, C is a weaken choice.

Logic: Aware beforehand so consumers buy more --> After increase consumers do not buy or buy at a normal rate --> hence the 'comparative' decrease.

Awareness is not an alternative explanation.
Why people buy more when they aware beforehand the imposition of the tax?
Because the tax will increase the retail price of the cigarette.

The logic above still tells that the effect of the tax is the cause of the consumption decrease. It strengthens the argument.

If you negate this logic, then you somehow weaken the argument.

soulwangh

Seems I was wrong.

Waiting for Ron's replying.

Don't worry. I will post his note.

soulwangh

soulwangh 发表于 2013-12-3 10:35
Seems I was wrong.

Waiting for Ron's replying.

RonPurewal wrote:

The argument focuses on the correlation between the volume of cigarette sales and the current price. (The argument just says "the price", but of course that means the current price, not a theoretical future price.)

If the consumers had been aware of the impending tax increase, then it's quite likely that they just loaded up on cigarettes while the price was still cheaper. In that case, their behavior would not have been motivated by the (current) price itself, but, rather, by the shadow of an impending price increase. (Once their stash is depleted, these consumers will presumably return to their normal buying behavior.)

My replying：
Hi, Ron

Thanks for replying!
You clarify one of my questions. Some questions still remain. Need help and correct my wrong reasoning!

1/
Now that current price is different form further theoretical price , I think C is indeed a potential correct choice. If people had loaded up cigarette the year before the tax was imposed, it is very reasonable to assume that when the tax was imposed, the volumes of cigarette sales decreased just because the stack of cigarette was not depleted rather than because the after-tax price were prohibitive.

I don't think C is wrong because" if A, then B" reasoning. The reason is in my NO.2 question. Need your justification.

Now, the only reason I find why C is wrong is this sentence:In contrast, in the year prior to the tax increase, sales had fallen one percent.

It has already ruled out the possibility that people loaded up cigarette by the impending price increase. C rules out a possible competing scenario that the stimulus has already done. Thus, C does not relatively strengthen the argument.

2/ What is your opinion about my reasoning as follows?
Am I correct?

Quote:
RonPurewal wrote:
anything disrupting the CAUSAL relationship between cigarette tax and cigarette consumption --> i.e., any ALTERNATIVE EXPLANATION FOR WHY THE TWO ARE CORRELATED --> will ruin the argument.
therefore, you can STRENGTHEN the argument by DISPENSING with such explanations.


Quote Ron‘s words:
this doesn't work. in general, the statements "if X happens, then Y will happen" and "if X doesn't happen, then Y won't happen" are unrelated to each other.


My Reasoning：
According to what you said, this question is a correlation to causation problem, and this kind reasoning assumes A is the only causal factor of B. If the choice can rule out any competing causal factor, it strengthens the argument.

IMO,the rule that the validity of "if A, then B" has nothing to do with the validity of "if not A, then not B" may not be applicable here. Because "if A, then B" reasoning does not require that A is the only causal factor of B.



RonPurewal        ：
        
Yeah. I somehow misread the argument last time -- I didn't notice that the sales decreased in both years cited. That rules out the idea of "loading up on cigarettes".

So, yes.

http://www.manhattangmat.com/forums/pack-of-cigarttes-and-tax-cr-t7354-15.html?sid=a47742915d710c237ff17c4bc3e0f1e5

兔tt

我还是没理解 求解答这个跟非a非b有什么区别 谢谢

739659010

文章需要加强的结论是销量和税后价格的关系，也就是税后价低销量高，反之亦然。
加税之前，香烟下降1%，销量呈下降趋势。加税之后下降10%，还是下降，只是更加剧烈。这个现象可能源自于行业自己的萎缩，也就是大家意识到香烟危害，减少购买香烟。但是B 控制了这个可能因素，支持了销量下降只能来自加税。
C项说消费者不知道要加税，在这个情况下还是无法解释为甚销量会一直下降。如果C项成立，那么消费者屯货的行为导致了加税之后销量下降。而不是单纯地税后价格高销量低，价格低销量高。

daisylol

739659010 发表于 2016-4-22 01:16
文章需要加强的结论是销量和税后价格的关系，也就是税后价低销量高，反之亦然。
加税之前，香烟下降1%，销 ...

同意！               

ceylon_

irenetopia 发表于 2013-11-16 18:49
这么想
问题问的是销售量的上升和烟税价格密切相关
问加强

同意！               

JustFuckingDoIt

感谢这楼的所有大神帮我解答这个疑惑，我也基于各位大神的观点，按照自己的理解给各位G友提供一个思考逻辑，希望能帮到大家。（如有错误，轻喷）

题目：sale下降是因为加tax了（完税价格= price + tax）
问题：加强
方向：排除他因

排除他因需要两个步骤：①这是个他因（他因变化可以引起目标变化）；②说明他因没有变。

B选项：他因1——“提醒顾客吸烟有害健康的信息” 没有变
对B选项取非思考：“提醒顾客吸烟有害健康的信息”变了会怎么样？
一般来说，顾客知道更多吸烟有害健康的信息，是可能会导致香烟的sales下降的。（不然印这个提醒在包装上就没意义了。）
所以“提醒顾客吸烟有害健康的信息” 是影响sales的一个他因，而B选项直接说了他因1不变，完成了排除他因的逻辑。


选项C：他因2——“人们没有意识到要加税”（或者说“人们的囤货行为”）
对C选项取非思考：人们意识到要加税会怎么样？
对于一个商品，准备加税（升价）了，那么顾客就会提前囤货，那么sales在加税前升高，加税后大家就不买或正常买，导致sales突然暴跌（下降11%）。
逻辑链条是：价格变化的信号（人们意识到将要加税）→ 人们囤货 → 加税，价格上升 → sales下降
也就是说，加税后的sales下降并不是加税导致的，只是加税前的囤货行为导致的
因此“人们意识到将要加税”（或者说“人们的囤货行为”）是影响sales的一个他因2。
【到这里完成了排除他因的第一步】

【排除他因第二步】
如果要加强，就要说明原因2“消费者的囤货行为”没变（排除他因）。
那么就要思考“消费者没有意识到将要加税” = “消费者没有囤货行为”吗？
RON的回答是：
If A, then will B.     即A → B
并不能推断出：If not A, then will not B.     即 非A → 非B
在逻辑中，A → B，只能保证 非B → 非A，不能保证 非A → 非B
因此，“消费者没有意识到将要加税” ≠ “消费者没有囤货行为”。
所以C选项并不能完成排除他因的逻辑链条。