LSAT 81, Logical Reasoning II, Q25, LSATHacks

LR Question 25 Explanation, by LSATHacks

QUESTION TEXT: If ecology and the physical sciences were evaluated by…

QUESTION TYPE: Parallel Reasoning

CONCLUSION: Ecology is being evaluated by different criteria than the physical sciences are.

REASONING: 

1. Same criteria —> ecology not successful
2. Ecology is a successful science

ANALYSIS: This argument uses a single conditional statement and the contrapositive to prove its point. Fact #2 above negates the necessary condition, which means we can negate the sufficient.

So look for answers with a single conditional + a fact, and a conclusion that negates one of the terms from the conditional. Only those answers can possibly be correct. 

Learning to skim for this structure is a vital skill. The right answer is near the end. If you spent a ton of time deeply considering the early answers, you’d waste much time on this question. True skill here involves seeing that most of the wrong answers are wrong for quick, structural reasons.

___________

1. I skipped this as soon as I read “either”. The stimulus didn’t have that, so this can’t possibly be right.
   Diagram: Tax increase —> Woodchip price up OR woodchip industry disappear
   Woodchip prices can’t rise, so the industry will disappear.
2. I skipped this as soon as I read “could” and “inclination”. They weren’t in the stimulus, so this can’t be right. “Could” is an unusual conditional term: it’s hypothetical. The stimulus was not hypothetical. Also, I wouldn’t say this is a good argument: lack of demand is a problem for the museum borrowing the works. The inclination of the lenders to lend will depend on how much the borrower pays: consumer demand is not their direct problem. Thus, the borrowing museum could misjudge demand, overpay for lending, and hold a failed exhibit.
   Diagram: Borrow Matisse —> Could have largest Matisse exhibit
   No demand, so no museum will lend.
3. This is a good argument, but it doesn’t use the contrapositive. Instead, the fact proves the sufficient, which proves the necessary.
   I read enough of the answer to see that, but didn’t spend much time on it beyond that. It’s important to know which answers to skip past, on a long question.
4. Be very wary of answers that match subject matter. It is absolutely irrelevant in parallel questions, and so usually it is used as a trap.
   This question negates the sufficient, and then negates the necessary: the flaw of incorrect negation. I skipped as soon as I saw it negated the sufficient.
5. CORRECT: This definitely matches: conditional statement, negation of necessary, proves the contrapositive.
   1. Economic theory adequate description —> forecasts possible
   2. Economic forecasts are not possible.
   
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   PT 81 /  PT 151

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