Necessary and Sufficient Assumptions Flashcards

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?

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.

A sufficient assumption answer choice on the LSAT will, when added to the argument's premises:

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.

Which of the following is a necessary assumption for the argument 'Since no evidence of fraud was found, the election was fair'?

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.

On Sufficient Assumption questions, correct answer choices are often characterized as:

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.

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:

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.

The negation test is considered most useful for:

Answer: Necessary Assumption questions

The negation test is specifically designed for Necessary Assumption questions to confirm that denying the assumption destroys the argument.

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?

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.