LSAT 103 | Section 1 | Logical Reasoning: Q24

LR Question 24 Explanation

QUESTION TEXT: That wall is supported by several joists. The only…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: At least one joist is broken.

REASONING: Only a broken joist could have caused that bulge.

ANALYSIS: This is a circular argument. In Circular arguments, the premise and the conclusion are the same.

Here’s a circular argument structure. “X must have caused Y because the only thing that could cause Y is X. “

The stimulus mirrors that structure: The joists must have caused the bulge because the only thing that could have caused the bulge is a joist.

Answer choice A has the same structure. The wrong answers are bad arguments, but they aren’t circular.

___________

1. CORRECT. The argument’s evidence is the same as its conclusion. This argument is circular, just like the stimulus.
    
   “A mistake made the conductor grimace, because only a mistake could do that.”
2. This is an incomplete argument. Maybe the orchestra had the most energy at the start and they avoided mistakes for that reason. But it isn’t a circular argument.
3. This isn’t a great argument. The argument hasn’t shown that the orchestra never plays well when they don’t like the music. But it isn’t circular.
4. This is only a good argument if we can also assume that the orchestra will play the piece as the composer specified. Otherwise they might just do without the harp. But this isn’t circular reasoning.
5. This is a bad argument. Maybe the conductor was angry because he thought about something his friend said. But it isn’t a circular argument.

Recap: The question begins with “That wall is supported by several joists The only”. It is a Parallel Reasoning question. Learn more about LSAT Parallel questions in our guide to LSAT Logical Reasoning question types.