SDCAR2010【逻辑入门】（八）Assumptions

sdcar2010

Sufficient assumption: with it, the conclusion will work; without it, the conclusion might or might not work.

Necessary assumption: without it, the conclusion will NOT work; with it, the conclusion might or might not work.

Statement: If this cat is yours, then it is a white cat.

Sufficient assumption: All of your cats are white.
Necessary assumption: At least one of your cats is white.

Hi, NN, that is very kind of u.
I have read the post, but i do not know why do we seperate sufficient assumptions from necessary assumptions?
I hardly distinguish them!!

-- by 会员 bitterbeauty (2011/10/7 21:13:14)

bitterbeauty

牛牛，sufficient和necessary分不清啊，牛牛给的例子看得很清楚，不过出在题目里面就分不清啦，感觉justify the conclusion 和 rely on the assumption差不多啊，求解答~

-- by 会员 dualtunnal (2011/7/15 22:15:12)

justify the conclusion: sufficient assumption

rely on the assumption: necessary assumption

-- by 会员 sdcar2010 (2011/7/16 0:03:39)

原来这里有...哈哈，明白了

freyang

Try this question:

The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.

Which of the following is an assumption on which the argument above depends?

(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.
(E) The primary purpose of the census is to analyze the economic status of the American population.

-- by 会员 sdcar2010 (2011/6/28 20:58:35)

Dear sdcar201,
I am confused about the answer B.  
According to my reasoning,  if B is negated,  that is to say,  some Americans are classified to a third class,  then the ratio of the poor to the rich to the third class can not be accurate even though some of the poor and of the rich are both uncounted.
Would you please give me a hand

sdcar2010

Necessary assumption. Use negation.

C is the right answer. If you negate C, then the basic statistical portrait of the nation painted by the census is NOT accurate since the missing poor and missing rich would distort the data.

B) when negated, can still make the conclusion work if what C) says is correct.

Basically, C) says if the mistaken percentage is the same for the rich and the poor, the census gives you a correct picture of the population.

Try this question:

The U.S. census is not perfect: thousands of Americans probably go uncounted. However, the basic statistical portrait of the nation painted by the census is accurate. Certainly some of the poor go uncounted, particularly the homeless; but some of the rich go uncounted as well, because they are often abroad or traveling between one residence and another.

Which of the following is an assumption on which the argument above depends?

(A) Both the rich and the poor have personal and economic reasons to avoid being counted by the census.
(B) All Americans may reasonably be classified as either poor or rich.
(C) The percentage of poor Americans uncounted by the census is close to the percentage of rich Americans uncounted.
(D) The number of homeless Americans is approximately equal to the number of rich Americans.
(E) The primary purpose of the census is to analyze the economic status of the American population.

-- by 会员 sdcar2010 (2011/6/28 20:58:35)

Dear sdcar201,
I am confused about the answer B.  
According to my reasoning,  if B is negated,  that is to say,  some Americans are classified to a third class,  then the ratio of the poor to the rich to the third class can not be accurate even though some of the poor and of the rich are both uncounted.
Would you please give me a hand

-- by 会员 freyang (2011/10/9 16:30:49)

chaseshi

8. When people evade income taxes by not declaring taxable income, a vicious cycle results.  Tax evasion forces lawmakers to raise income tax rates, which causes the tax burden on non-evading taxpayers to become heavier.  This, in turn, encourages even more taxpayers to evade income taxes by hiding taxable income.

The vicious cycle described above could not result unless which of the following were true?

(D) No one who routinely hides some taxable income can be induced by a lowering of tax rates to stop hiding such income unless fines for evaders are raised at the same time.
-------------------------------------------------------------------------------------------------------------------------

LZ, just wondering is "Tax evasion forces lawmakers to raise income tax rates, which causes the tax burden on non-evading taxpayers to become heavier." the conclusion of the argument? And is the last sentence just the inference?

Secondly, why is selection D wrong? Does the sentence "...by a lowering of tax rates" try to contradict the conclusion?

bonfin

up

blueday5

Hi, NN, 我看了好一段时间才把Sufficient assumption和Necessary assumption想通

但是充分假设和必要假设要怎么实际应用到做题呢？



例如,

2. A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.
The researcher's conclusion depends on which of the following assumptions?
(A) High immune-system activity protects against mental illness better than normal immune system activity does.
(B) Mental illness is similar to physical disease in its effects on body systems.
(C) People with high immune-system activity cannot develop mental illness.
(D) Mental illness does not cause people's immune system activity to decrease.
(E) Psychological treatment of mental illness is not as effective as is medical treatment.



通过题目说：The researcher's conclusion depends on which of the following assumptions?

我知道这题是在问必要假设

想请问接下来看选项时，Sufficient Assumption or Necessary Assumption 还有其他功用吗？



我现在的困惑是，看了LZ在#13的解释, 既然每道题都直接拿来negation，能weaken到原题即答案的话，为什么还需要去区别做题时看到的Assumption属于Sufficient或Necessary呢？(如果这样, 我仔细研究如何分辨Sufficient还是Necessary不就白忙一场了吗？)



不懂啊~~~，请求NN 再说明一下

无敌西红柿炒蛋

Hi,Sdcar!
For Q 1,the premise is "33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them".  And  the main conclusion is "drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are drivers who do not."
If my judgement is correct, and what's the gap between the premise and the conclusion. In view,through the condition and the premise ,we can logically deduce the conclusion.
Could you explain it explicitly ?This question confuse me a lot.
THX

sdcar2010

Hi,Sdcar!
For Q 1,the premise is "33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them".  And  the main conclusion is "drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are drivers who do not."
If my judgement is correct, and what's the gap between the premise and the conclusion. In view,through the condition and the premise ,we can logically deduce the conclusion.
Could you explain it explicitly ?This question confuse me a lot.
THX

-- by 会员 无敌西红柿炒蛋 (2011/11/1 17:23:49)

What if the policeman hates those drivers who install radar detector and gives them speeding tickets whenever the policeman sees any of them???

sdcar2010

Hi, NN, 我看了好一段时间才把Sufficient assumption和Necessary assumption想通

但是充分假设和必要假设要怎么实际应用到做题呢？



例如,

2. A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity. The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.
The researcher's conclusion depends on which of the following assumptions?
(A) High immune-system activity protects against mental illness better than normal immune system activity does.
(B) Mental illness is similar to physical disease in its effects on body systems.
(C) People with high immune-system activity cannot develop mental illness.
(D) Mental illness does not cause people's immune system activity to decrease.
(E) Psychological treatment of mental illness is not as effective as is medical treatment.



通过题目说：The researcher's conclusion depends on which of the following assumptions?

我知道这题是在问必要假设

想请问接下来看选项时，Sufficient Assumption or Necessary Assumption 还有其他功用吗？



我现在的困惑是，看了LZ在#13的解释, 既然每道题都直接拿来negation，能weaken到原题即答案的话，为什么还需要去区别做题时看到的Assumption属于Sufficient或Necessary呢？(如果这样, 我仔细研究如何分辨Sufficient还是Necessary不就白忙一场了吗？)



不懂啊~~~，请求NN 再说明一下

-- by 会员 blueday5 (2011/10/31 20:11:04)

Since all those problems I posted are NECESSARY assumption questions. Therefore, negation is used for all of them. If you see a sufficient assumption question, DO NOT use negation method.

Try this one:

The average thirty-year-old Chinese will have watched more than ten thousand TV commercials in his or her lifetime. Therefore, the TV commercial has influenced Chinese way of thinking.

The conclusion above follows logically if which one of the following is assumed?
A) The way of thinking which people develop are largely determined by external influences.
B) Anything people are exposed to in great quantity will influence their way of thinking.
C) It is impossible to avoid or ignore TV commercials.
D) Some peole find TV commercials more interesting to watch than the news broadcast every night.
E) Certain form of communication to which people are subjected will affect their way of thinking.