Critical Reasoning
Verbal
13 min readWelcome to the study of weakening arguments. This guide is built for the absolute beginner. If you have never studied Critical Reasoning before, you are in the right place. By the end, you will know exactly what a weakening question is, how to attack it, and how to avoid the traps the GMAT sets for you.
A weakening question asks you to do one simple thing: make the argument's conclusion less likely to be true. The GMAT presents a short argument, and then asks you to pick the answer choice that most seriously weakens that argument. The correct answer is not necessarily a statement that proves the conclusion false. It is a statement that introduces doubt, uncertainty, or a reason to question the logic.
Why does the GMAT test this? Because in business, you will constantly be presented with proposals, sales pitches, and strategies. A good manager does not just accept an argument because it sounds good. A good manager asks: What could be wrong here? What are we not considering? What would make this plan fail? Weakening questions measure your ability to find the flaw in a line of reasoning.
Every argument in Critical Reasoning has two basic parts: premises and a conclusion. The premises are the evidence, facts, or statements given to support the conclusion. The conclusion is the main point the author is trying to convince you of. The author uses the premises as support for the conclusion.
For example, consider this argument:
"Our company's sales increased by 20% last month. We also launched a new advertising campaign last month. Therefore, the new campaign caused the sales increase."
Here, the premises are the sales increase and the campaign launch. The conclusion is that the campaign caused the sales increase. The gap in this argument is the assumption that the campaign was the reason for the sales increase. There could be other reasons: a competitor went out of business, a holiday season, or a price drop.
In many arguments, the conclusion is a causal claim: X caused Y. To weaken a causal claim, you can show that something else caused Y, that X did not happen, or that the relationship is reversed. In other arguments, the conclusion is a general statement based on a sample. To weaken that, you can show the sample is unrepresentative. In still others, the conclusion is a recommendation. To weaken it, you can show that the recommended action will not achieve the desired goal or will have harmful side effects.
You will know you are dealing with a weakening question when you see certain phrases in the question stem. The stem is the part that asks the question. Look for these signals:
Any of these phrases indicates a weaken question. The words "weaken," "undermine," "call into question," "cast doubt," and "challenge" are all synonyms in this context. When you see them, you know your task.
Follow this process for every weakening question. With practice, it will become automatic.
Ask yourself: What is the author trying to convince me of? Look for conclusion keywords like "therefore," "thus," "hence," "so," "consequently," or "as a result." Sometimes the conclusion is not introduced by a keyword. In that case, ask: What is the main point?
What evidence is given? What facts are stated? These are the premises. Underline them or jot them down. The premises are the support for the conclusion.
What must be true for the premises to lead to the conclusion? This is the assumption. The gap is usually something the author takes for granted. For example, if the premises say "Sales increased" and the conclusion says "The campaign caused it," the assumption is that no other factor caused the increase.
Before you look at the answer choices, think: What would make the conclusion less likely? What would attack the assumption? For the sales example, a weakener would be: "A major competitor closed its doors last month." That gives an alternative cause for the sales increase.
Read each answer choice and ask: Does this make the conclusion less likely? If yes, it is a candidate. If no, eliminate it. Be careful: many answer choices will be irrelevant or even strengthen the argument. The correct answer must directly affect the conclusion.
Now let's look at the common patterns you will see in the answer choices. The GMAT is predictable. Once you know the traps, you can avoid them.
Many answer choices will be true but have nothing to do with the argument. They might talk about a different group, a different time, or a different product. For example, in an argument about car safety, an answer choice about truck safety is irrelevant. The correct answer must be about the same subject as the conclusion.
Some answer choices will actually support the conclusion. They will be the opposite of what you need. For example, in the sales campaign argument, an answer choice that says "No other advertising was done last month" would strengthen the causal claim. Read carefully and ask: Does this help or hurt the conclusion?
Be cautious of answer choices that use words like "all," "none," "always," or "never." They are often too strong and may be wrong. The correct weakener does not need to be absolute. It just needs to introduce doubt.
Sometimes an answer choice will directly state that the conclusion is false. That sounds great, but it may be too obvious. The GMAT often includes such an answer as a trap. It might be too extreme or not supported by the premises. The correct weakener usually offers a subtle alternative explanation or a missing piece of evidence.
An answer choice that introduces a new concept that is not discussed in the argument is usually wrong. For example, if the argument is about employee productivity, an answer about employee morale might be out of scope unless morale is directly linked to productivity. Always ask: Does this affect the conclusion?
Argument: "Last year, the city increased the number of police officers on the streets. At the same time, the crime rate decreased by 15%. Therefore, the increase in police officers caused the decrease in crime."
Question: Which of the following, if true, most weakens the argument?
Step 1: Conclusion: The increase in police officers caused the crime decrease.
Step 2: Premises: More officers, crime decreased.
Step 3: Assumption: No other factor caused the crime decrease.
Step 4: Prediction: Something else caused the crime decrease.
Step 5: Evaluate choices:
Answer: A or B. In a real question, you would pick the one that most directly attacks the causal link. Here, both A and B do that. A gives a specific alternative cause. B shows a pre-existing trend. Either would weaken. The correct answer would be the one that is most relevant and direct.
Argument: "A survey of 500 students at a large university found that 80% prefer online classes. Therefore, most students in the country prefer online classes."
Question: Which of the following, if true, most weakens the argument?
Step 1: Conclusion: Most students in the country prefer online classes.
Step 2: Premises: Survey of 500 students at one university, 80% prefer online.
Step 3: Assumption: The sample is representative of all students.
Step 4: Prediction: The sample is not representative.
Step 5: Evaluate choices:
Answer: B. It directly attacks the representativeness of the sample.
Argument: "All swans are white. I have seen a swan, and it was white. Therefore, the next swan I see will be white."
Question: Which of the following, if true, most weakens the argument?
Step 1: Conclusion: The next swan will be white.
Step 2: Premises: All swans are white (a claim), and the speaker saw a white swan.
Step 3: Assumption: The claim "all swans are white" is true, and the next swan will follow the pattern.
Step 4: Prediction: A black swan exists.
Step 5: Evaluate choices:
Answer: A. It provides direct counterevidence.
At the sub-505 level, the correct answer is usually straightforward. But there are a few nuances to keep in mind.
The question stem will often say "most weakens" or "most seriously undermines." This means there may be more than one answer that weakens, but you must pick the one that does so the most. The correct answer will be the one that has the strongest impact on the conclusion. The others will be weaker or less direct.
The biggest trap at this level is choosing an answer that is true but irrelevant. For example, in the police argument, an answer about the city's budget is irrelevant. To avoid this trap, always ask: Does this affect the conclusion? If not, eliminate.
Sometimes the conclusion is a recommendation or a plan. For example: "We should buy more computers because our employees are less productive." To weaken this, you could show that the computers will not solve the productivity problem. The weakener attacks the effectiveness of the recommendation.
Now you have the foundation. Go ahead and try some practice questions. Remember, the more you practice, the faster you will spot the gap and the weakener.
Free Critical Reasoning questions on this topic — try a few now.