LSAT 159 | Section 1 | Logical Reasoning: Q21

LR Question 21 Explanation

QUESTION TEXT: Professor O’Brien: Any of my students who heard Mercado’s …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Some of my students heard the lecture from the beginning.

REASONING: Any of my students who heard it from the beginning would find it fascinating. Some of my students found it fascinating.

ANALYSIS: This argument makes a simple sufficient-necessary incorrect reversal. The entire difficulty is that the right answer is worded strangely. Let’s imagine there are only two students.

1. Sue: She is Professor O’Brien’s student. She didn’t go to the lecture, but heard about it, and thought it was fascinating.
2. Emma: Not Professor O’Brien’s student. Did go to the lecture from the beginning, did think it was fascinating. She was the only student at the lecture.

This example is 100% consistent with what O’Brien says. Some of her students (Sue) thought the lecture was fascinating, but Sue wasn’t even at the lecture. And the lecture’s only attendee, Emma, was not O’Brien’s student.

___________

1. Professor O’Brien didn’t say all of her students went to the lecture and found it fascinating. She only said some did, so it doesn’t matter if some others didn’t.
2. O’Brien’s rule was only about O’Brien’s students, not everyone. So if some other people who weren’t O’Brien’s students didn’t find the lecture fascinating, that is irrelevant to O’Brien’s argument.
3. Same as A. O’Brien’s claim is only that at least some of her students were at the lecture from the beginning. It does not matter if some others were not.
4. CORRECT. The double negatives make this hard. This answer says: “None of Professor O’Brien’s students were at the lecture from the beginning and found it fascinating.”
    
   This is true! O’Brien made a very bad argument.
5. Even so, some other students could still have been there from the beginning and heard it.