LSAT Necessary and Sufficient Assumptions 3 — Questions and Answers
Question 1: Argument: 'City parks improve mental health. Residents of Millbrook have poor mental health. Therefore, Millbrook should build more parks.' Which assumption is NECESSARY for this argument?
- All mental health problems stem from lack of green space
- Building parks in Millbrook will improve residents' mental health (Correct answer)
- Millbrook residents spend time outdoors regularly
- Parks are less expensive than mental health clinics
Correct answer: Building parks in Millbrook will improve residents' mental health
The argument requires that parks built in Millbrook will actually improve mental health there, connecting the general evidence to the specific recommendation.
Question 2: A sufficient assumption answer choice on the LSAT will, when added to the argument's premises:
- Raise a new objection to the conclusion
- Make the conclusion logically certain (Correct answer)
- Weaken one of the existing premises
- Identify a flaw in the argument's structure
Correct answer: Make the conclusion logically certain
A sufficient assumption makes the argument deductively valid—the conclusion cannot be false if the premises and the assumption are all true.
Question 3: Which of the following is a necessary assumption for the argument 'Since no evidence of fraud was found, the election was fair'?
- The election officials were honest
- If the election were unfair, evidence of fraud would have been found (Correct answer)
- Voters were satisfied with the outcome
- The ballots were counted accurately
Correct answer: If the election were unfair, evidence of fraud would have been found
The argument assumes that fraud leaves detectable evidence; without this, the absence of evidence wouldn't indicate absence of fraud.
Question 4: On Sufficient Assumption questions, correct answer choices are often characterized as:
- Narrow statements limited to a single case
- Broader conditional statements that cover the argument's logical gap (Correct answer)
- Restatements of a premise already in the argument
- Weakenings of the argument's conclusion
Correct answer: Broader conditional statements that cover the argument's logical gap
Sufficient assumption answers tend to be broader 'if-then' statements that, when plugged in, guarantee the conclusion logically follows.
Question 5: Argument: 'This painting uses techniques common only in 17th-century Dutch masters. Therefore, this painting was made in the 17th century.' A necessary assumption is:
- The painting is valuable
- No modern artist can replicate 17th-century Dutch techniques (Correct answer)
- Dutch masters are more skilled than modern painters
- The techniques were invented in Holland
Correct answer: No modern artist can replicate 17th-century Dutch techniques
If a modern artist could use those techniques, the fact that the painting uses them wouldn't prove it's from the 17th century.
Question 6: The negation test is considered most useful for:
- Sufficient Assumption questions
- Necessary Assumption questions (Correct answer)
- Strengthen questions
- Weaken questions
Correct answer: Necessary Assumption questions
The negation test is specifically designed for Necessary Assumption questions to confirm that denying the assumption destroys the argument.
Question 7: Argument: 'Residents who exercise regularly have lower stress. The new recreation center will encourage residents to exercise. So the recreation center will lower stress among residents.' Which is a sufficient assumption for this argument?
- The recreation center will be affordable for all residents
- Any increase in regular exercise among residents will lower their stress levels (Correct answer)
- Stress is the primary health concern of residents
- The recreation center will be the only exercise facility in town
Correct answer: Any increase in regular exercise among residents will lower their stress levels
This assumption bridges the chain: more exercise from the center → lower stress, making the conclusion logically follow.
LSAT Necessary and Sufficient Assumptions 3
Argument: 'City parks improve mental health.
Residents of Millbrook have poor mental health.
Therefore, Millbrook should build more parks.' Which assumption is NECESSARY for this argument?