LR Question 11 Explanation
QUESTION TEXT: Inspector: The only fingerprints on the premises…
QUESTION TYPE: Flawed Parallel Reasoning
CONCLUSION: The thief must have worn gloves.
REASONING: The only fingerprints in the building belong to the owner, Mr. Tannisch.
ANALYSIS: The first rule of detective stories is that anyone is a suspect. Yes, there could have been a thief with gloves. Or maybe there are no other prints because….Mr Tannisch is the thief!
The detective improperly excludes the owner from suspicion, without giving a reason why.
To parallel this argument, you need to find a situation where the author incorrectly excludes a possible suspect.
___________
- CORRECT. This ignores the obvious possibility that the camp cafeteria made everyone sick.
- This doesn’t ignore an obvious, named suspect. Instead, it ignores a possible (unnamed) alternate cause. For instance, maybe the inclement weather was worse when the second prototype was tested.
- This is a different error. It’s true that an individual swimmer has low odds of winning. But there will always be one winner out of a group. There’s a 100% chance of someone winning the meet.
- This is possible, but incomplete. We’d need more information about what can cause cavities. This argument isn’t like the stimulus, it doesn’t exclude any obvious suspect.
- This is a bad argument. Maybe peas are different from tomatoes. But it doesn’t exclude any obvious suspect.
More Resources for Flawed Parallel Reasoning Questions
- Conditional Reasoning Article: Learn about conditional statements.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Flaw drills: Practice identifying flaws.
- Intro Course lesson: This intro course lesson covers Flawed Parallel Reasoning questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers flawed parallel reasoning questions.
LOL thanks! I hope the LSAT isn’t assuming we know this kind of stuff on wiki pages (pretty sure grinding teeth, which is the same/similar action to chewing, can lead to cavities via wearing the enamel though so I wouldn’t say it’s totally obvious that chewing only on one side couldn’t lead to cavities). So you’re saying if D were the same in the first sentence but then replaced the second (“Hence, she must chew more on the left side than on the right”) with something like “Hence, she must have a genetic defect on the left but not the right”, it could be right or would you still say there’s anything about A that makes it better? Or is it just that as you say it’s more of an obvious, “duh” type, answer? I guess I’ll stop trying to think too much about some of these and look for more “duh” answers :)
In general, don’t look for reasons why answers COULD be right. They should in fact be “duh”, obviously that matches.
To parallel this argument, there should be anOBVIOUS alternative that’s being ignored. D simply doesn’t have that, and it would be hard to construct one for teeth precisely because much about them is not common knowledge.
The way I looked at the initial flaw in the argument was not that it could have been someone else necessarily (though I did think of that)…but that it could have been the case that, say, the person wiped down the prints rather than wearing gloves…
So…I thought D could be the answer because maybe rather than it being chewing as the issue, it was that, say, she didn’t brush her teeth on that side or that there’s some genetic defect that affects only one side.. So to me, D seemed better because it still left out other possibilities for the issue (cavities) just like the original left out other possibilities for the issue (another thief (as you say) or a thief wiping the place down). I don’t really get your explanation that D is wrong because it doesn’t tell us what could cause cavities….it implies that chewing can. And on that note, what does the original say causes the diamonds to go missing? A person wearing gloves??? I don’t see how these are different.
The reason I thought A was a worse choice was that it had a negation – so “must NOT have been” vs. the “must chew” in D and the “must have worn” in the original.
Any further thoughts you have on the above would be greatly appreciated!
That’s a good point about wiping prints. I’d say there are a couple problems with that + your explanation for D.
1. It is *very* hard to wipe down all prints compared to wearing gloves.
In practice we touch a lot of surfaces. Gloves easily avoid prints. Wiping down prints is a much, much harder and actually kind of implausible.
It’s not impossible, just note that you’re making an *implausible* alternate explanation. Meanwhile you’re excluding a very plausible alternate explanation.
So to parallel that you’d need a case where there was a plausible alternate explanation, and also an implausible one.
D simply fails to match this. My point about cavities is that there’s no evidence chewing is the main cause of cavities. That’s not the sort of thing you can assume from outside knowledge. You say the argument “implies” this is true, but implying something doesn’t make it valid evidence unless it’s something we can assume.
Meanwhile there’s no plausible alternate explanation or implausible one. I’d say you’re trying to hard to fit your view of the argument into an answer choice. Parallels should fit *easily*.
A person wearing gloves is a very plausible cause of diamonds going missing. Diamonds don’t vanish randomly. Either a thief does it, or someone misplaces them. These are valid assumptions from outside knowledge.
This is in part a common sense question. The LSAC has been using these more recently. You have to think like a normal human to solve these. Any normal situation viewing this setup would ask “What if Mr. Tannisch stole his guest’s diamonds”?
Note: The actual causes of cavities are bacteria, fermentation, and genetic defects. Chewing doesn’t really enter into it: https://en.wikipedia.org/wiki/Dental_caries#Cause