Logical reasoning PrepTest 137 · Section 4 · Question 24

Incorrect. Nightbirds used a style indistinguishable from Larocque's, so establishing that almost all of his students painted in a similar style to him would (if anything) strengthen the argument that one of them painted this painting.

Incorrect. Without establishing if Larocque's students did sign their paintings, this answer doesn't do much for the argument. Even if it did establish that they did sign their paintings, this would be a pretty weak answer, as there's any number of reasons that they wouldn't have signed one that was in Larocque's style.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Experts agree that Nightbird was painted by Larocque or a student of his. The painting contains orpiment, which no known Larocque has, so the painting must be by a student.

Answer Anticipation:
This argument uses a common method of reasoning to reach its conclusion—ruling out alternatives. In order to effectively use this method of reasoning, an argument must establish an exhaustive list of possible alternatives, and then effectively eliminate all but one.

Let's start with the first criteria—does it establish a complete list of alternatives? It notes that experts agree that this painting is either by Larocque or one of his students, and no one else could have done it ("if it was not . . . "). If the experts are correct, then the considered list is complete. An answer might suggest the experts are wrong, but it does appear as if the author is appealing to the appropriate experts, so this is not the most likely answer.

Now, the second criteria—does the argument effectively eliminate all but one option? Here, since there are only two options (Larocque, a student), it only needs to eliminate one. And it attempts to eliminate Larocque as an option by stating that no known painting by him has a certain pigment in it. While that certainly provides evidence that this might not be a Larocque, it's hardly definitive. So any answer that calls into question this connection between the pigment and it being by a student of Larocque instead of the master himself will serve to weaken the argument.

Answer Explanation:
The argument rules out Larocque as the artist behind Nightbird because he wasn't known to use orpiment. If the same is true of all of his students, then the same logic would rule each of them out as the artist. This weakens the conclusion by showing the information that allowed one possibility to be eliminated would do the same to the other, and thus that information can't justify the conclusion.

Key Takeaway:
An argument that proceeds by eliminating alternatives needs to do two things to be valid—establish a complete list of alternatives, and effectively eliminate all but one. If the argument is missing either of those pieces, it's the flaw in the argument.

Incorrect. Their importance isn't related to whether or not they painted this painting, so this answer is out of scope.

Incorrect. If anything, this would provide evidence that a painter after Larocque—say, one of his students—painted Nightbird.