Hi Thang.

Please find below an OG question where weakener doesn't disprove the conclusion. Or, in other words, it would require us to make assumptions to disprove the conclusion.

(Posted on according-to-the-tristate-transportation-authority-making-113718.html)
According to the Tristate Transportation Authority, making certain improvements to the main commuter rail line
would increase ridership dramatically. The authority plans to finance these improvements over the course of five
years by raising automobile tolls on the two high-way bridges along the route the rail line serves. Although the
proposed improvements are indeed needed, the authority’s plan for securing the necessary funds should be
rejected because it would unfairly force drivers to absorb the entire cost of something from which they receive no
benefit.

1.. Which of the following, if true, would cast the most doubt on the effectiveness of the authority’s plan to
finance the proposed improvements by increasing bridge tolls?
(A) Before the authority increases tolls on any of the area bridges, it is required by law to hold public hearings at
which objections to the proposed increase can be raised.
(B) Whenever bridge tolls are increased, the authority must pay a private contractor to adjust the automated
toll-collecting machines.
(C) Between the time a proposed toll increase is announced and the time the increase is actually put into effect,
many commuters buy more tokens than usual to postpone the effects of the increase.
(D) When tolls were last increased on the two bridges in question, almost 20 percent of the regular commuter
traffic switched to a slightly longer alternative route that has since been improved.
(E) The chairman of the authority is a member of the Tristate Automobile Club that has registered strong
opposition to the proposed toll increase.

The asnwer is Option D. One very obvious assumption required in this question is that past trends will be followed in the future too.


And below is the OG question where weakener does shatter the conclusion:
(Posted on unlike-the-wholesale-price-of-raw-wool-the-wholesale-price-93250.html)

Unlike the wholesale price of raw wool, the wholesale price of raw cotton has fallen considerably in the last Year.
Thus, although the retail price of cotton clothing at retail cloting stores has not yet fallen, it will inevitably fall.
Which of the following, if true, most seriously weakens the argument above?

A. The cost of processing raw cotton for cloth has increased during the last Year.
B. The wholesale price is typically higher than that of the same volume of raw cotton.
C. The operating costs of the average retail cloting store have remained constant during the last year.
D. Changes in retail prices always lag behind changes in wholesale prices.
E. The cost of harvesting raw cotton has increased in the last year.

The answer is Option A.

Since, as per the weakener, the cost of processing raw cotton for cloth has increased during the last Year, we cannot say that "retail price of cotton will inevitably fall". It might or it might not fall (depends how much processing costs has increased).

As far as your reasoning goes, it is precisely right. Whether a statement increased doubt or shatters the conclusion, in both the cases, it is a weakener.

Hope this helps

Thanks,
Chiranjeev
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dear e gmat expert.

if in the second og , oa A is changed to
cost of processing of raw cotton increases much more than the price of raw cotton reduces

we have a situation in which a weakener truely shatter the conclusion.

but could you pls cite an og question which presents this case of shattering?

thank you e gmat experts.

In CR questions we deal with real world scenarios. New information will either strengthen or weaken or do nothing to the conclusion. It is very very difficult for the new info to establish something without a doubt because then the new info will need to consider all possible cases. There will always be some assumptions. The new info will change the degree of confidence in our conclusion. It will not establish or refute our conclusion without any doubt.

Let me explain using an example:

Your argument: Mr X was found on the crime scene (I have been watching too much Fox Crime lately!) with a gun in his hand, blood on his clothes and victim on the floor. Mr X must be the killer (your conclusion).

I want to weaken your argument: Mr X was trying to coerce the gun out of the killer's hand. He is not the killer.
(I have successfully cast doubt on your conclusion but there are assumptions here. You can still get back. )

Your argument: But we can say without a doubt that there was no other person in that room during that time. (perhaps there is a single exit/entry point and it was guarded) Now you have strengthened your case and weakened mine but still there are assumptions.

My argument: The victim was trying to kill himself and Mr X was trying to stop him. The victim succeeded in committing suicide. Mr X is innocent.
Now I have weakened your case and strengthened mine.

We can keep at it for a long time and every new piece of info can strengthen/weaken the argument. Every new piece of info does come with assumptions. That is why, criminals are punished when their crime is established without REASONABLE doubt.

Basically, it will be very very difficult to disprove a conclusion. You can generally just weaken it.
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