LSAT Logic Reasoning 5 — Questions and Answers
Question 1: A judge instructs: 'If new evidence is presented, the case will be reopened. The case was not reopened.' What can be concluded?
- New evidence was presented but rejected.
- No new evidence was presented. (Correct answer)
- The defendant waived the right to present evidence.
- The judge violated procedural rules.
Correct answer: No new evidence was presented.
Applying modus tollens: the case was not reopened (consequent false), so no new evidence was presented (antecedent false).
Question 2: The argument 'We should legalize marijuana because prohibition has failed, just as alcohol prohibition failed in the 1920s' relies primarily on which reasoning technique?
- Deductive reasoning from established legal principles.
- Analogical reasoning between two historical cases. (Correct answer)
- Statistical induction from a large data set.
- Appeal to authority by citing historical consensus.
Correct answer: Analogical reasoning between two historical cases.
The argument draws a parallel between two historical prohibition situations, inferring that what happened with alcohol will apply to marijuana.
Question 3: Which of the following, if true, most strengthens the argument that mandatory sentencing laws reduce violent crime?
- States that enacted mandatory sentencing also improved their economies during the same period.
- Violent crime rates fell in states with mandatory sentencing but remained flat in comparable states without such laws. (Correct answer)
- Judges in mandatory-sentencing states report feeling constrained in their rulings.
- Mandatory sentencing laws are popular with voters in most regions.
Correct answer: Violent crime rates fell in states with mandatory sentencing but remained flat in comparable states without such laws.
A controlled comparison showing crime fell under mandatory sentencing but not without it provides direct causal evidence for the claim.
Question 4: A scientist argues: 'This new species must be carnivorous because it has sharp teeth, and all previously discovered members of its genus are carnivorous.' This is an example of:
- A deductively valid argument with certain conclusion.
- An inductively strong argument whose conclusion is probable but not certain. (Correct answer)
- A circular argument that assumes what it tries to prove.
- A fallacious appeal to tradition.
Correct answer: An inductively strong argument whose conclusion is probable but not certain.
The conclusion is supported by genus-wide patterns and anatomical evidence, making it inductively strong but not deductively certain since exceptions are possible.
Question 5: Which flaw undermines the following argument: 'Students at elite universities earn higher salaries, so attending an elite university causes higher earnings'?
- It commits a hasty generalization from too few cases.
- It ignores that high-earning students may self-select into elite universities. (Correct answer)
- It appeals to authority by referencing prestigious institutions.
- It uses equivocal language in the term 'elite.'
Correct answer: It ignores that high-earning students may self-select into elite universities.
If high-achieving, well-connected students disproportionately attend elite schools, the school may not be the cause of earnings — pre-existing traits may be.
Question 6: In LSAT logical reasoning, a 'necessary assumption' differs from a 'sufficient assumption' in that a necessary assumption:
- Alone guarantees the conclusion is true.
- Must be true for the argument to work, but does not alone prove the conclusion. (Correct answer)
- Strengthens the argument without being required for it.
- Provides a counterexample that weakens the argument.
Correct answer: Must be true for the argument to work, but does not alone prove the conclusion.
A necessary assumption is one the argument cannot do without — if it's false, the argument fails — but it alone doesn't prove the conclusion.
Question 7: An argument states: 'Crime rates dropped after the city installed more streetlights. Therefore, more streetlights reduce crime.' Which additional fact, if true, most seriously undermines this conclusion?
- The streetlights were installed in high-crime neighborhoods.
- The city also deployed 200 additional police officers at the same time as the streetlights. (Correct answer)
- Residents reported feeling safer after the streetlights were installed.
- Similar cities with streetlights also experienced crime reductions.
Correct answer: The city also deployed 200 additional police officers at the same time as the streetlights.
If additional police were deployed simultaneously, they — not the streetlights — may have caused the crime reduction, making the causal link to streetlights unreliable.
LSAT Logic Reasoning 5
A judge instructs: 'If new evidence is presented, the case will be reopened.
The case was not reopened.' What can be concluded?