LSAT 142 | Section 2 | Logical Reasoning: Q23

QUESTION TEXT: Every brick house on River Street has a front yard…

QUESTION TYPE: Flawed Parallel Reasoning

CONCLUSION: Most brick houses have two stories.

BH (most) ➞ 2S

REASONING: Brick houses have front yards. Most houses with front yards have two stories.

• BH ➞ F
• F (most) ➞ 2S

ANALYSIS: This argument makes a very common LSAT error. It tries to attach a “most” statement onto the necessary conditional of a conditional statement. (Front yards)

You can’t do that. You can only connect “most” statements with sufficient conditions. (Brick houses)

Why? Because there could be, say, 11 brick houses, and 1000 houses with front yards. It’s possible that most houses with front yards aren’t brick. So it could be true that, for example, “Most houses with front yards are easily flammable”. We could have 6 brick houses with front yards, and 501 houses with front yards which are easily flammable. Those houses might not be brick: they could all be wood houses!

Whereas if you say: “most expensive houses are made of brick”, then you could properly conclude “most expensive houses have front yards” (because they are brick: “Expensive (most) ➞ BH ➞ F”. This is just an example, “expensive” isn’t a term in the argument)

Every answer talks about some combination of public servants, legislators, politicians, and running for office. Keeping the structure in mind is the key to answering this question quickly. You’re looking for:

1. A conditional statement.
2. A “most” statement that matches the necessary condition
3. A conclusion that incorrectly combines the sufficient condition with the “most” statement.

Note: Since it’s clear the question is only talking about river street, you can just leave “river street” off your diagram; it’s superfluous. Keep your diagrams simple.

___________

1. L ➞ P, L (most) ➞ R
    
   Conclusion: P (most)➞ R
    
   Not the same, as the “most” statement is the same as the sufficient condition.
    
   We’re looking for one that’s the same as the necessary condition.
2. Two most statements, no conditionals. This can’t possibly be parallel. I didn’t even finish reading this worthless answer. Be ruthless; if an answer doesn’t match structure, it’s out.
3. Evidence: L ➞ P, P some L
    
   Conclusion: P some RO
    
   This isn’t the same at all. I skipped this answer immediately when I read “not every”, since the argument in the stimulus used a “most” statement and this answer doesn’t talk about most.
    
   It’s possible for the correct answer to be some other concept instead of most (e.g. almost all), but it’s rare. And this answer wasn’t parallel. If the argument had said “P some RO” as evidence and “L some RO” as evidence, then it would have been largely parallel. 

4. CORRECT. This parallels exactly. There is a conditional statement, with a “most” statement that shares the same term as the necessary condition.

   The conclusion incorrectly tries to combine the sufficient with the “most” statement.

   Evidence:

   • L ➞ P
   • P (most) ➞ R

   Conclusion: L (most) ➞ R

5. Same as B. Two “most” statements, no conditionals. This can’t possibly be parallel. I didn’t even finish reading this useless answer. Be ruthless; if an answer doesn’t match structure, it’s out.

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