LSAT Necessary and Sufficient Assumptions 2 — Questions and Answers
Question 1: An argument concludes that a new drug will reduce hospital readmissions. The argument assumes the drug's effects in clinical trials will mirror its effects in the general population. This assumption is best described as:
- A sufficient assumption because it alone guarantees the conclusion
- A necessary assumption because without it the conclusion cannot follow (Correct answer)
- Neither necessary nor sufficient because the conclusion could be true regardless
- Both necessary and sufficient, making it the only relevant assumption
Correct answer: A necessary assumption because without it the conclusion cannot follow
The assumption is necessary because if trial results don't generalize, the conclusion that the drug reduces readmissions in practice cannot follow.
Question 2: On the LSAT, when a question asks 'The argument depends on which assumption?' it is asking for a:
- Sufficient assumption
- Necessary assumption (Correct answer)
- Conditional assumption
- Causal assumption
Correct answer: Necessary assumption
The word 'depends on' signals a necessary assumption—something the argument cannot do without.
Question 3: Which technique is most reliable for identifying a necessary assumption?
- Add the assumption to the premises and verify the conclusion follows
- Negate the assumption and check if the argument falls apart (Correct answer)
- Strengthen the conclusion by adding new evidence
- Find an alternative explanation for the conclusion
Correct answer: Negate the assumption and check if the argument falls apart
The negation test works by denying the assumption—if this destroys the argument, the assumption is necessary.
Question 4: Argument: 'All students who pass the bar exam become licensed attorneys. Jordan passed the bar exam. Therefore, Jordan is a licensed attorney.' What type of assumption, if any, does this argument require?
- A necessary assumption that Jordan studied law
- A sufficient assumption about Jordan's character
- No unstated assumption—the conclusion is deductively guaranteed (Correct answer)
- A necessary assumption that the bar exam is difficult
Correct answer: No unstated assumption—the conclusion is deductively guaranteed
This is a valid deductive argument; the conclusion follows necessarily from the stated premises without any hidden assumption.
Question 5: A sufficient assumption differs from a necessary assumption in that a sufficient assumption:
- Must be true for the conclusion to hold
- Guarantees the conclusion when added to the premises (Correct answer)
- Is always stated explicitly in the argument
- Weakens the conclusion when negated
Correct answer: Guarantees the conclusion when added to the premises
A sufficient assumption, when combined with the premises, is strong enough on its own to guarantee the conclusion.
Question 6: An argument states: 'Employees who receive mentorship advance faster. We want our employees to advance faster. Therefore, we should implement a mentorship program.' The gap in this argument is best bridged by assuming:
- All employees want to advance faster in their careers
- A mentorship program will actually result in employees receiving mentorship (Correct answer)
- Mentorship is the only way to accelerate employee advancement
- The company can afford a mentorship program
Correct answer: A mentorship program will actually result in employees receiving mentorship
The argument needs the assumption that implementing the program leads to mentorship actually occurring, bridging the plan to the desired outcome.
Question 7: When using the negation test on a proposed necessary assumption and the argument still seems valid, what can you conclude?
- The assumption is necessary and you should select it
- The assumption is sufficient but not necessary
- The assumption is not necessary for the argument (Correct answer)
- The argument has no assumptions
Correct answer: The assumption is not necessary for the argument
If negating the assumption doesn't damage the argument, that assumption is not necessary—it isn't something the argument depends on.
