Q22 - Merle: Usually when I insert a dollar bill

[Laura Damone]

Question Type:
Match the Flaw

Stimulus Breakdown:
Conclusion: The electric outlet is usually turned on.

Evidence: Usually when Merle puts a dollar into the change machine, it squeaks. It can squeak only when the electric outlet is on.

Answer Anticipation:
Since this is a Match the Flaw question, Identifying the flaw is my first priority. From these premises we can logically infer that the electric outlet is usually on when Merle puts a dollar in. But the argument concludes that the outlet is usually on, as in, it's on most of the time. I don't have a name for this flaw, but we could say the argument should conclude something is true in some circumstances but instead projects it onto most circumstances.

Another option would be to diagram this argument out. When I have to match an argument that is a series of conditional statements, I always diagram them. This argument has both conditional and quantified statements, but I have a system for diagramming quantified statements, so let's go for it:

evidence: insert dollar --most--> squeaks --> outlet on
conclusion: time --most--> outlet on

Our correct answer should display the same pattern of "quantifier math" connecting evidence and conclusion, with one premise that's an "all" statement, one that's a "most" statement, and a conclusion that's a "most" statement. Quantifier mismatches are grounds for elimination!

Correct answer:
D

Answer choice analysis:
(A) No "most" statements. Eliminate!

(B) A "some" statement. Eliminate!

(C) Two "many" statements. Eliminate!

(D) This answer has two "most" statements and an "all" statement, so it passes the first test. Let's dig deeper. We could diagram this out like so:
p: read new novel --most--> found disturbing --> have vivid imagination
c: people --most--> have vivid imagination
That's a match! This argument should conclude that most people who read the new novel had a vivid imagination, not that most people in general have a vivid imagination.

(E) Uh oh. This answer also has two "most" statements and an "all" statement, so it passes the first test, too. Let's dig deeper. We could diagram this out like so:
p: read new novel --most--> found disturbing --> have vivid imagination
c: have vivid imagination --most--> found disturbing
Nope. This argument is flawed because it illegally reverses the last premise and sticks a most in there. It doesn't take what would be a valid conclusion if it applied to a narrow circumstance and apply it to most circumstances.

Takeaway/Pattern:
Hooray for quantifier math! This is one of the trickiest concepts tested on the LSAT. And while it typically only shows up once or twice per test and only on hard questions, those who are targeting a top score should be comfortable with the concept. If you've got our 5lb. Book of LSAT Practice Drills, check out the "Quanti-YAY or Quanti-NAY" drills on pages 565 and 952.

#officialexplanation

[LeonC641]

Hi Manhatten Prep,
I picked the correct answer but was being troubled diagramming (A). Could you show the diagram of its conditional logic? Thanks!