Logical reasoning PrepTest 143 · Section 4 · Question 11

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Most approve of proposal → Airport built
But it's unlikely most will approve of the proposal.
Therefore: The airport is unlikely to be built.

Answer Anticipation:
The argument establishes a conditional rule, and then it treats the negation of the sufficient condition as resulting in the negation of the necessary condition. That's an illegal negation, so we should find the answer reflecting that.

Answer Explanation:
The argument establishes that a majority of Dalton residents approving of the proposal is sufficient for the airport to be built. However, it then concludes that the airport probably won't be built because it probably won't get that approval. In treating the absence of approval as tanking the airport, the argument is treating that approval as necessary for the airport to be built. While this answer is more closely associated with an illegal reversal, it can describe an illegal negation, as well—the two flaws are, in essence, the contrapositive of each other, which makes them logically equivalent.

Key Takeaway:
There's some overlap in answer choices for illegal reversals and illegal negations, as they both utilize the same type of flawed logic. In general, when an Errors in Reasoning question has conditional logic, it's probably flawed in how it applies it, and you should start by narrowing down the answers to ones that discuss this type of logic, and then make your determination from there as to which is correct.

Incorrect. What most people are established to believe is that the airport would create noise problems, and this is driving their opposition to a proposal. First, the argument doesn't conclude that the airport will create noise problems—just that it probably won't be built. Second, the argument sets up people's approval as the means by which the airport can be approved, so their belief—and not the reality of the situation—is what is relevant.

Incorrect. The conclusion of this argument is that it's "unlikely" the airport will be built, so it doesn't conclude that an event will not occur.

Incorrect. The conditional rule that's established as governing the likelihood of the airport being built is about only the residents of Dalton, not those who live nearby, so how they feel is out of scope.

Incorrect. There's no indication that the people of Dalton would believe this, or care about it, or rank it as being more important than the noise problems, so this answer is out of scope.