LSAT Logic Reasoning 4 — Questions and Answers
Question 1: A conditional argument states: 'If the eyewitness testimony is unreliable, the jury should acquit. The jury convicted.' What can be logically inferred?
- The eyewitness testimony was reliable. (Correct answer)
- The eyewitness testimony was unreliable.
- The jury ignored the evidence.
- The defendant was actually guilty.
Correct answer: The eyewitness testimony was reliable.
By contrapositive, if the jury did NOT acquit, then the testimony was NOT unreliable — meaning it was reliable.
Question 2: A nonprofit claims: 'Our tutoring program raised average test scores by 15 points.' A critic responds: 'But students who scored below 50 points showed no improvement.' Which rhetorical strategy does the critic employ?
- Pointing to a counterexample that challenges the general claim. (Correct answer)
- Committing an ad hominem attack on the nonprofit.
- Using a slippery slope to predict future failures.
- Appealing to irrelevant statistics to confuse the audience.
Correct answer: Pointing to a counterexample that challenges the general claim.
By showing a subgroup for whom the claim does not hold, the critic provides a counterexample that limits or undermines the generalization.
Question 3: Which of the following most accurately describes the logical structure of an argument by analogy?
- Two cases share relevant properties, so what is true of one is likely true of the other. (Correct answer)
- A general rule is applied deductively to a specific instance.
- The absence of evidence against a claim is treated as evidence for it.
- A conclusion is supported by citing the opinions of recognized experts.
Correct answer: Two cases share relevant properties, so what is true of one is likely true of the other.
An argument by analogy infers that because two cases share key similarities, a conclusion that applies to one probably applies to the other.
Question 4: Passage: 'Every contract requires offer, acceptance, and consideration. This agreement has offer and acceptance but no consideration.' The strongest conclusion is:
- This agreement is a valid contract.
- This agreement is not a valid contract. (Correct answer)
- This agreement can be enforced at the court's discretion.
- This agreement lacks offer and acceptance.
Correct answer: This agreement is not a valid contract.
Since consideration is a necessary element and is missing, the agreement fails to meet the criteria for a valid contract.
Question 5: An LSAT argument concludes that a new drug is safe because it passed three clinical trials. Which consideration most undermines this conclusion?
- The trials were conducted over a period of two years.
- The trials excluded patients over 65, who are the drug's primary intended users. (Correct answer)
- The drug was developed by a for-profit pharmaceutical company.
- Two of the three trials were double-blind.
Correct answer: The trials excluded patients over 65, who are the drug's primary intended users.
If the primary users were excluded from trials, safety data may not apply to them, directly weakening the safety conclusion.
Question 6: A city council argues: 'We must either raise taxes or cut services. We cannot cut services. Therefore, we must raise taxes.' This argument is:
- Invalid because it presents a false dilemma.
- Valid as a disjunctive syllogism if the disjunction is exhaustive. (Correct answer)
- Invalid because it affirms the antecedent.
- Valid only if the tax increase is proportional.
Correct answer: Valid as a disjunctive syllogism if the disjunction is exhaustive.
A disjunctive syllogism is valid when one option of an exhaustive either/or is eliminated, leaving the other as the conclusion.
Question 7: Which of the following most accurately describes the method of reasoning called 'modus tollens'?
- If P then Q; P is true; therefore Q is true.
- If P then Q; Q is false; therefore P is false. (Correct answer)
- If P then Q; Q is true; therefore P is true.
- If P then Q; P is false; therefore Q is false.
Correct answer: If P then Q; Q is false; therefore P is false.
Modus tollens denies the consequent to deny the antecedent: if the 'then' part is false, the 'if' part must also be false.
LSAT Logic Reasoning 4
A conditional argument states: 'If the eyewitness testimony is unreliable, the jury should acquit.
The jury convicted.' What can be logically inferred?