Critical Reasoning: weakening arguments

A weaken answer can do several things:

• Offer an alternative explanation for the evidence.
• Show that the evidence is unreliable or unrepresentative.
• Show that the proposed cause did not occur.
• Show that the effect occurred even without the cause.
• Introduce a factor that reverses the expected outcome.
• Show that the conclusion is too broad for the evidence.

The answer must affect the reasoning. A fact about the same topic can be irrelevant if it does not change the likelihood of the conclusion.

Many arguments claim that A caused B because A happened before B. A weaken answer can show that C caused B. If a company's sales rose after a new ad campaign, a weaken answer could show that a major competitor went out of business at the same time, leaving more customers for the company.

When an argument generalizes from a sample, a weaken answer can show that the sample is biased. If a survey of gym members finds that most people exercise daily, a weaken answer could show that the survey was conducted at a gym during peak hours. The sample does not represent the general population.

A weaken answer can also show that the sample is too small or that the respondents were self-selected. These facts reduce the support the evidence provides.

Some arguments rely on data that may be inaccurate. A weaken answer can show that the measurement was flawed, that the data came from an unreliable source, or that the terms were defined differently. If a study finds that a drug reduces symptoms, a weaken answer could show that the study participants also received another treatment.

Be careful not to weaken the premise itself. On the GMAT, the evidence is usually taken as true. The correct weaken answer attacks the link between the evidence and the conclusion, not the factual accuracy of the evidence unless the argument explicitly relies on the source's reliability.

If an argument says A caused B, a weaken answer can suggest that B caused A. For example, a study finds that people who exercise regularly report better moods. The argument concludes that exercise improves mood. A weaken answer could suggest that people who are already in a good mood are more likely to exercise. The causal direction may be reversed.

A weaken answer can show that the conclusion is too broad. If the evidence comes from one city, a weaken answer could show that conditions in other cities are different. If the conclusion says "all," a single exception may be enough to weaken it, although the GMAT usually prefers a choice that affects the argument's main support.

Degree matters. A choice that shows a small exception may weaken the argument slightly. A choice that shows the main evidence is unreliable weakens it substantially. Compare the remaining choices and choose the one that does the most damage.

A choice that restates the evidence does not weaken the argument. A choice that is merely consistent with the conclusion does not weaken it. A choice that supports the argument is the opposite of what you need. A choice that introduces a new topic does not affect the reasoning.

Some choices weaken a different conclusion. Read the conclusion carefully and make sure the choice attacks the actual claim.

To weaken a causal claim, show that the effect occurred without the cause, that the cause occurred without the effect, or that a third factor explains both. A study that finds a correlation between two variables is vulnerable to all three attacks. For example, if a company claims that a new bonus increased productivity, a weaken answer could show that productivity also rose in divisions that did not receive the bonus. This suggests a broader trend rather than a bonus effect.

Another way to weaken a causal claim is to show that the timing is wrong. If the effect began before the cause was introduced, the cause cannot explain it. If the effect continued after the cause was removed, the causal link is less likely. Timing evidence is often decisive because it is hard to explain away.

A recommendation can be weakened by showing that the proposed action will not solve the problem, that it will create a larger problem, or that a better alternative exists. If a company recommends cutting prices to increase revenue, a weaken answer could show that demand is inelastic, so lower prices will reduce revenue rather than increase it.

Be careful with choices that describe a cost. Every recommendation has costs. A choice weakens only if the cost is large enough to outweigh the benefit or if it undermines the proposed mechanism. A minor drawback is not enough.

More than one choice may weaken the argument. The GMAT asks for the choice that most weakens. Prefer the choice that attacks the central assumption. A fact that creates doubt about a side issue is less powerful than a fact that offers a complete alternative explanation.

1. Identify the conclusion and the evidence.
2. State the assumption or the gap that connects them.
3. Predict a fact that would undermine the gap.
4. Eliminate choices that support the argument or are irrelevant.
5. Compare the remaining choices by how directly they weaken the link.
6. Choose the choice that makes the conclusion least likely.

• Choosing a choice that attacks the evidence instead of the reasoning.
• Choosing a choice that is true but irrelevant.
• Choosing a choice that weakens a different conclusion.
• Confusing a small exception with a decisive weakness.
• Ignoring an alternative cause that the passage already rules out.
• Choosing a choice that simply restates the evidence.