GMAT Critical Reasoning, GMAT Verbal
Comments 2

Critical Reasoning: Strengthen-Weaken — Type 2

In the previous post on the Strengthen-Weaken question type, we discussed that there were three argument types around which strengthen-weaken type of questions are posed

  • Plan of Action (PoA)
  • X causes Y
  • Correlation-Causation

We discussed the PoA type of argument in that post, in this one we will look at the second type – X causes Y.

Argument Type – X causes Y
Another standard argument type is one that can be classified as the X causes Y type. It goes without saying that the X causes Y type is the same as X does not cause Y in terms of structure.

All critical reasoning arguments are constructed on the basis of premises: Premise 1 + Premise 2 = Argument

The premises can be data, facts or judgments used to make an argument/conclusion/claim/assertion/proposal/contention(or any other word used to describe the argument made on the basis of the premises).

So if the argument follows the structure

Premise 1 + Premise 2 = X causes/does not cause Y,

then the strengthen=weaken options will revolve around 2 types of options — data-based premises that qualifying existing premises or additional an premise that cites another cause.

Data-based premises Additional data that supports/completes the data-based premise used to make the argument Additional data that contradicts or shows that data-based premises used to make the argument are incorrect/incomplete
Additional Premise New information that brings in additional reasons to prove X causes Y or rules  other possible reasons for Y New information that suggests that Z could also be the cause for Y, making the argument X causes Y vulnerable.

Let us take a few sample GMAT questions to understand how these patterns play out.

Option Type 1: Data-based

Strengthen Question                                                                                                                            A chemical company claims that, since only one of 520 rats that were given high doses of a new artificial sweetener developed cancer while all the others remained healthy, the sweetener is not carcinogenic for human beings and ought to be approved for human consumption.

Which of the following, if true, most strongly supports the chemical company’s claim?

(A) Chemicals that are carcinogenic for rats are usually also carcinogenic for other animals, such as guinea pigs, used in experiments.
(B) The spontaneous incidence of cancer in this particular strain of rat is approximately one in 540.
(C) Tests conducted on a certain strain of mouse show that, of 500 mice given a dose of sweetener similar to that given the rats, 53 developed cancer.
(D) Certain chemicals that are carcinogenic for human beings have been shown not to be carcinogenic for rats.
(E) The average lifespan of the strain of rat used in the experiment is 2 years; the chemical company terminated the experiment when the rats were 13 months old.

This argument that falls into the X causes/does not cause Y category can be broken down as follows:

Premise 1: Only one of 520 rats that were given high doses of a new artificial sweetener developed cancer while all the others remained healthy.

Argument: Sweetener is not carcinogenic for (does not cause cancer in) humans

Since the premise is a data-based premise, only 1 in 520 developed cancer, the strengthen option will provide additional data that

  • completes the existing data or
  • shows that existing data has been properly drawn.

A weaken option will show that existing data

  • is incorrect
  • has been improperly drawn
  •  or provide data that runs counter to the data used

Options (C) weakens the argument by providing data that runs counter to the one used in the argument — another experiment where 53 out of 500 mice developed cancer.

Option (E) weakens the argument by showing that data has been improperly drawn — experiment was terminated mid-way through the life-span, data might have been different if experiment were conducted till the full life-span of the rats.

Option (D) weakens this by bringing in an additional premise — safe for rats does not mean safe for humans.

Option (A) seems like it is strengthening the argument but is not. The argument is trying to show that it is safe for rats, so safe for humans. If option (A) should support it, it should show that it is safe for many other animals as well. Instead data supporting the opposite argument, unsafe for rats, unsafe for other animals as well.

Only option (B) provides data-based support for the argument. The spontaneous incidence (normal levels of cancer without any sweetener) is 1 in 540.

The question is providing the “with sweetener” data while the option is giving you the “without sweetener” data so that the numbers given can be seen in perspective.

The change from 1/540 to 1/520 is barely anything in numerical terms, which means that sweetener is not increasing the rate of cancer in these rats and hence supports the argument.

What if option (B) said, the normal rate of cancer in this strain of rats is 1 in 10000? This definitely makes the sweetener dangerous as it is increasing the rate of cancer by almost 20 times.

Option Type 2: Additional Premise

Strengthen Question
Many television viewers own videocassette recorders (VCR’s). Companies that advertise on television complain that VCR ownership hurts their business, since a VCR makes it possible to view television programs without watching the commercials. Indeed, two-thirds of those who tape programs on a VCR edit out the commercials when viewing the programs.

Which of the following, if true, would most strengthen the companies’ complaint that VCR ownership is currently hurting their business?

(A) The methods for determining audience size, which in turn determines charges for advertising time, count households that are merely recording a program as households that are watching it.
(B) VCR manufacturers who advertise on television would themselves suffer the damage, if any, to advertisers’ interests that is caused by VCR’s.
(C) There are VCR’s that are in the early stages of development that will automatically edit out commercials during the recording process.
(D) Those who tape programs on VCR’s, but who do not edit out commercials when viewing the programs, tape more often than those who do edit out the commercials.
(E) Some television commercials are as entertaining or informative as the programs they interrupt.

The next pattern in strengthen-weaken question with respect to X causes Y type of argument is the additional premise type.

The argument falls into X causes Y type — VCR ownership is currently hurting their business or VCR ownership is currently causing business damage to advertisers

The strengthen option will be an additional premise that will be pointing in the same direction.

It is important to note that the additional premise need not use or have the same terms as used in the passage. So watch out before you label options as irrelevant, you should evaluate each option for its impact on the argument.

Do not choose an option just because it contains the same terms, as in the case of option (B).

It uses circular reasoning — if it causes damage, VCR companies that advertise will also suffer damage. So what is option saying, is it causing damage or is it not causing damage? It is just saying drawing out the deduction if the argument is true. It is not giving evidence to prove that the argument is true.

Option (C) is incorrect as it talks about VCRs in the future and not those currently in use but the argument talks about VCRs currently hurting the advertisers’ business.

Option (D) says that those who tape frequently edit fewer number of times, a situation that weakens the argument.

Option (A) offers an additional premise that supports the argument. It says that when companies pay for advertising they are paying even for viewers who are not watching. So not only are VCRs resulting in  fewer people watching their ads and hence affecting revenues, but also resulting in lower profits since they are still paying the same amount in cost. So earlier if 100 people watched, they paid for 100. Now only 50 are watching, which is a reason why they argue that VCRs are hurting their business, but still they are paying for 100, which is the information that option provides.

Weaken Question
Recently political pressure groups have become far more effective at persuading industrial corporations to change. For example, as a result of the efforts of animal rights groups, many pharmaceutical and cosmetics companies have reduced their use of laboratory animals, substituting in their place alternative methods of product testing.

Which of the following, if true, casts the most serious doubt on the connection between pressure group activity and corporate change claimed above?

(A) Many companies in the pharmaceutical industry have increased their public relations spending in order to counter the activity of animal rights groups.
(B) Before the new methods of testing products are used, they have to be calibrated by comparison tests involving experiments on laboratory animals.
(C) When companies stop using laboratory animals, they generally go to some expense to publicise this change of policy.
(D) The pharmaceutical manufacturers who still use laboratory animals are mostly the smaller firms that have been less subject to pressure group activity.
(E) The methods of product testing that do not involve laboratory animals are faster and cheaper than the methods that do.

When it comes to weaken questions revolving around the X causes Y type the option will usually show that Z also can be linked to Y or Z can be the cause of Y.

The above argument can be deconstructed as follows:

Premise 1: As a result of the efforts of animal rights groups, many pharmaceutical and cosmetics companies have reduced their use of laboratory animals

Premise 2: Substituting in their place alternative methods of product testing

Argument: Political pressure groups have become far more effective at persuading industrial corporations to change or pressure groups are causing corporate change

The correct option should show that there might be some other reason behind this.

Option (A) says that many companies are increasing their PR spend to counter the activities. Is the PR to show that they have changed and rebuild their public image damaged by pressure group activity (like the latest Nestle ad). But the argument uses information that shows that many companies have changed, so many companies increasing their PR spend does not weaken the argument.

Option (B) talks about using animal testing during the transition to other methods, as long as they are switching to other methods it does not weaken the argument.

Option (E) clearly offers an additional premise related to the premise used in support of the argument — the alternate methods are faster and cheaper, weakening the argument which attributes pressure group activity as the reason.

Usually the two arguments types discussed in this post and the previous one are the most common argument types you will find on the Strengthen-Weaken question type.

Please go through the Official Guide or the Verbal Review and try to connect the questions to these two patterns.

Once you are able to consistently identify the pattern you will see a marked rise in your speed and accuracy on these two question types.


  1. Pingback: Critical Reasoning: Strengthen-Weaken — Type 3 | The GMAT Blogger

  2. Pranit says

    Hello sir ! The following is one of the problems that I incurred while solving the paper based test. Need your advice on, how to approach this problem.

    It is well known that human tears often serve to moisten the eye, protect it from infection, and wash away irritants; such tears are called irritant or reflex tears. Dr. Field hypothesizes that emotional tears have a different biological function. She suggests that by shedding tears when under emotional stress people excrete harmful chemicals that build up in such body fluids as blood serum during emotional stress.

    Each of the following, if true, provides some support for Dr. Field’s hypothesis EXCEPT:

    (A) The people most likely to cry when undergoing emotional stress are less likely to suffer from stress-related diseases than is the population at large.
    (B) If a local anesthetic is applied to the surface of the eye, irritant and reflex tears are inhibited, but emotional tears are not.
    (C) The chemical composition of tears that are induced by grit in the eye is identical to the composition of tears induced by emotional stress.
    (D) The concentration of a substance that the body produces only under conditions of emotional stress is thirty times greater in tears than in blood serum.
    (E) Patients who suffer from a condition that prevents secretion of tears display a slower than normal physiological recovery from emotional stress.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s