Critical Reasoning

Mental model

Deconstruct the argument into Premise (facts) + Assumption (unspoken link) = Conclusion.

Every argument has a gap between its facts and its conclusion. Your job is to find that invisible assumption. Strengthening an argument means verifying the assumption; weakening it means attacking the assumption.

Method

1. Read the question stem first to know your goal (Strengthen, Weaken, Find Assumption, or Infer).
2. Identify the Conclusion (the author's main claim) and the Premise (the evidence provided).
3. Spot the Assumption: What must be true for the Premise to logically lead to the Conclusion?
4. Evaluate options against the Assumption. For 'Weaken' questions, find the option that breaks the link. For 'Assumption' questions, find the option the author implicitly relies on.
5. Eliminate out-of-scope options that do not directly address the logic gap.

Worked example

Problem: Argument: The new UI reduces clicks to checkout. Therefore, our revenue will increase. Question: What weakens this argument?

1. Identify the goal: Weaken the argument.
2. Identify Premise: New UI reduces clicks to checkout.
3. Identify Conclusion: Revenue will increase.
4. Spot the Assumption: Reduced clicks lead to more completed purchases (and thus more revenue).
5. Formulate attack: What if fewer clicks actually hurt sales? (e.g., users accidentally buy and refund, or users feel rushed and abandon).
6. Select option matching attack: 'Customers often abandon carts if they feel the checkout process lacks security steps.'

Answer: Customers often abandon carts if they feel the checkout process lacks security steps.

Shortcuts

• In 'Weaken' questions, the correct answer introduces new information that attacks the assumption, not the premise. Never argue with the premise.
• In 'Inference' questions, the correct answer must be 100% true based ONLY on the facts given. Avoid any leaps of logic.

Common mistakes

• Attacking the Premise: Trying to weaken an argument by saying the evidence is false. In critical reasoning, you must accept the premise as fact and attack the logic linking it to the conclusion.
• Choosing 'Out of Scope' answers: Picking an option that sounds smart but addresses a different demographic, timeframe, or topic than the argument.

Glossary

premise

A fact or piece of evidence given in an argument to support a claim.

weaken

To make an argument less convincing by attacking its assumptions.

strengthen

To make an argument more convincing by proving its assumptions are true.

Recall questions

• What is the formula for a standard argument in critical reasoning?
• When asked to weaken an argument, what specific part of the argument should you attack?
• In an 'Inference' question, are you allowed to use outside knowledge to reach a conclusion?

Questions & answers

Premise: City A implemented a bike-sharing program. Traffic dropped 10%. Conclusion: Bike-sharing programs reduce traffic. What is the assumption?

The drop in traffic was not caused by another factor, like a new highway or economic downturn.

Approach: Find the gap. The author assumes correlation (bikes and traffic drop) implies causation. The assumption rules out alternate causes.

Premise: All servers run Linux. Server X crashed. Inference: Did Server X run Linux?

Yes.

Approach: Apply pure deductive logic. If all servers run Linux, and X is a server, then X runs Linux. No outside assumptions needed.

Continue learning

Previous: Reading Comprehension

Return to Aptitude Roadmap